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THE TBMPLB PRIMERS
MODERN CHEMISTRY Systematic By
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fcresenteD to
of tbe
of {Toronto
Mrs. W. E.
-U vl
!E
THE TBMPLB PRIMERS
MODERN CHEMISTRY Systematic By
WILLIAM RAMSAY,
D.Sc.
JOHN DALTON
mODERH CHEMISTRY SYSTEMATIC
RAmSAY-DS?
1900* t9&SO BEDFORD-STREET
1
'
All rights reserved
.
'
/,
MODERN CHEMISTRY SECOND PART SYSTEMATIC CHEMISTRY
CHAPTER
I
Methods of Preparing Elements
Their Physical
Properties.
Mixtures and Compounds.
In the olden days, no was drawn between a compound and a mixture. " substances " Indeed, all impure artificially prepared were It was termed " mixts." after the true idea of eledistinction
only
ments had been arrived
at,
and indeed not
until
Dalton had
formulated the laws which go by his name, that the distinction was drawn. The ultimate criterion for combination is definiteness of proportion, and this is generally connected with uniformity in properties, or homogeneity. substance is said to be homogeneous when no one part of it But this may differs from any other part in composition. be predicated of glass, or of air, which are mixtures, and not mixture may be homogeneous ; a comcompounds.
A
A
pound must. Again, it
is usually accepted that the separation of the constituents of a mixture may be effected by mechanical, or
at least
by physical means ; whereas the separation of the from a compound require chemical treatment.
elements
Here VOL.
it II.
is
difficult
to
draw
a
sharp distinction.
A
The
MODERN CHEMISTRY
2
separation of carbon dioxide from soda-water by the application of heat is similar in character to the separation of sugar from water by evaporation of the water ; yet we believe that a solution of carbon dioxide in water consti-
compound, while that of sugar in water is a mere It is necessary to be guided mixture of the two. by analogy in the former case ; and it is probable that the compound named carbonic acid is really contained in a solution of carbon dioxide in water, on account of the formulae and behaviour of the carbonates. The Atmosphere. In the case of mixtures of gases, For in this case, each the problem becomes an easier one.
tutes a
gas retains
example,
is
its
individual properties.
The
atmosphere, for
believed to be a mixture of the gases
Nitrogen,
.
.
Oxygen, Argon, &c.,
.
.
.
.
78.16 per 20.90 0.94
cent.
100.00 amounts of water-vapour, of carbon dioxide, and of ammonia, all of which vary considerably in amount, be
if small
subtracted.
This can be shown by First, The density of
several lines of argument. air agrees
with the mean of the
which Thus, the density of the mixture of atmosin 40,000 from pheric nitrogen and argon differs by only I part that calculated from their relative weights, and the proportion This is the case with compound gases in which they occur.
densities of
its
constituents, taken in the proportion in
they occur.
only when the constituents are present by volume, as in hydrogen chloride,
mixture
is
far
from
in
equal proportions
HCL
The
above
fulfilling that
requirement. Second, The constituents of air can be separated by diffusion. Thomas Graham discovered that the rate of
escape of gases through an opening, or of passage through
THE ATMOSPHERE
3
a porous partition is inversely in the order of the square roots of their relative densities. Now, air has been enriched in
oxygen and
passes
more
the last
two
in
rapidly
argon by diffusion
m the proportion
the lighter nitrogen
;
I
c
of
i
i
,
:
Vi4
fractions referring to the rates
j==
:
-~ V2O
\/i6 of oxygen and
argon respectively; the oxygen and argon, being more slowly diffusible, are left to the last.
Third,
The
of
constituents
air
While oxygen
solution in water.
is
may
be separated by
soluble at atmospheric
temperature in the proportion of about 3 volumes in 100 of about i 5 volumes ; water, nitrogen is much less soluble and argon about 4. i volumes. Hence, on shaking air with .
water, the relative volumes dissolved are
Oxygen,
3
x 20.90
;
:
Nitrogen, 1.5 x 78.16
;
and
Argon, 4.1 x 0.9 4, It is evident the proportion of 63 : 1 17 3.8. the relative proportion of nitrogen has considerably
in
I
t
:
reased.
j ourth, The elements contained in air are not present in To ascertain the relative number of any atomic ratio. atoms of these elements it is necessary to divide the percentage amount of each by its atomic weight ; thus we have
78.16
Nitrogen,
L
=
^ 5.58
;
20. Q
2=
Oxygen,
'
Argon,
94
=
0.024
1.31
;
it)
14 ;
4
and these numbers bear to
ea-ch other
no simple
ratio.
Lastly, it is possible by distilling liquid air to separate the more volatile nitrogen from the less volatile oxygen
and argon.
For that air
these reasons, and other similar ones, is a mixture.
it is
concluded
MODERN CHEMISTRY
4
The Analysis of the Atmosphere is, however, always performed by chemical means, for the difference in physical properties of its constituents is not sufficiently marked to allow of their being utilised for purposes of Many common elements unite easily with separation. oxygen to form non-volatile compounds, when they are One of the most convenient for this heated in air. By passing a known volume purpose is metallic copper. of air over copper turnings, contained in a counterpoised tube of hard glass, and heated to redness, the oxygen of the air is removed, for it combines with the copper to form non-volatile black oxide of copper. The increase in weight of this tube gives the weight of the oxygen in But it is customary to analyse the measured volume of air. volumetrically by absorbing the oxygen from a known volume by means of burning phosphorus, or of a solution of potassium pyrogallate the remainder consists of a mixture of The separation of these nitrogen, argon and its congeners. gases from each other is described in the next paragraph. Reference has already been made in Part I. to the different processes which may be used for the isolation of elements from their compounds. But there exists a group of elements, that of which the first member is helium, which form no compounds, and which therefore are found only in a free state. air
:
therefore, convenient to begin with these. These elements are all gases at Group. the ordinary temperature of the atmosphere, and they are It
is,
The
HELIUM
consequently
all
to be found in atmospheric air.
They
are
colourless, even in the liquid condition, and are devoid of smell and taste. They are very sparingly soluble in water ;
example, I oo volumes of water dissolve only 4. 1 volumes Their preparation consists, first, in the of argon at 15. separation of the other constituents of air from them, and, second, in their separation from each other. Air, which is a mixture, and not a compound, of nitro-
for
gen, oxygen, carbon dioxide, ammonia, water-vapour, and the gases of the helium group, is a supporter of combustion,
.
THE HELIUM GROUP
5
owing to the combination of the oxygen which it contains with most other elements. Now, when air passed through a tube full of a mixture of caustic soda and lime, to remove carbon dioxide, and then through a U-tube containing sulphuric acid, to deprive it of water- vapour and ammonia, is led over red-hot copper, or over some other red-hot metal which unites with oxygen, the oxygen is retained, and nitrogen with
members of the helium group alone passes on. The nitrogen can be removed in one of two ways. The first plan is due Cavendish, who attempted to prove that atmospheric nitroHe mixed atmospheric gen was a homogeneous substance. nitrogen with oxygen, and passed electric sparks through the mixture, having a little caustic soda present in the tube. Under the influence of the sparks, the nitrogen and to
NO
this comoxygen combine, giving nitride peroxide, 2 pound is absorbed by the soda, with formation of sodium nitrate and nitrite, NaNO and NaNO 2 Cavendish 3 obtained a residue of not more than one-hundred-andtwentieth of the nitrogen and he concluded that if atmospheric nitrogen was not homogeneous, it contained only ;
.
;
a trace of another gas. The second plan is to pass the atmospheric nitrogen over red-hot magnesium, or, better, over a mixture of magnesium powder and lime, which gives calcium ; the magnesium or the calcium unites with the
nitrogen, and the inert gases pass on. To separate these gases from each other, they are compressed into a bulb, cooled by being immersed
10185
in
a liquid, in
The
argon, krypton, and xenon condense to which the neon and helium are dissolved. On
liquid air.
removing the bulb from the liquid air, its temperature rises, and the helium and neon escape first, mixed with a large amount of argon. Argon distils next, and krypton and xenon remain till the last. By frequently repeating this process of " fractional the and xenon distillation," argon, krypton, can be separated from each other, and from the helium and neon which still remain mixed with each other, for both are gases at the of boiling air. temperature
MODERN CHEMISTRY
6
To
separate helium from neon, recourse must be had to liquefy hydrogen, the process is in
liquid hydrogen.
To
same
as that for liquefying air, described on hydrogen, compressed by a pressure of 200 205 by passing through a coil of atmospheres, is cooled to copper pipe, immersed in liquid air boiling under low On expanding, its temperature is still further pressure. lowered, and the still colder gas, in passing upwards, cools the tubes through which the compressed gas is passing. The hydrogen finally issues in the liquid state, as a colourless, mobile liquid, of the approximate temperature 240. By its aid, if a mixture of neon and helium is cooled to 240, the former freezes, while the latter remains The gaseous helium can be removed with the gaseous. pump and the neon, after it has been warmed, may also be
principle the
The
p. 26.
;
pumped off in a pure state. Helium can also be prepared by
heating certain specimens of pitchblende or uraninite, a mineral consisting chiefly of oxide of uranium. The gas, which appears to exist in some sort of combination with the uranium oxide, escapes ; it All these gases give very striking contains a trace of argon. spectra, and that of helium was observed during the solar eclipse of 1868 in the chromosphere, or coloured atmosphere, of the sun. Although at that time it had not been dis-
covered on the earth, the name the bright yellow line, which its
is
"
'< helium was given to the most characteristic of
spectrum.
As in air,
regards the relative amount of these gases contained 100 volumes of air contain 0.937 v ume f tne l
mixture.
the largest portion of this mixture is argon ; probably the volume of all the others taken together does not exceed one-four-hundredth part of that of the
argon.
xenon
By
far
Indeed, it may be said with truth that there than there is gold in sea-water.
is
less
in air
Methods of Separating Elements from their Compounds. The methods of preparation of the remaining elements depend on consideration^ of the cost of the
SEPARATION PROCESSES
7
compound from which the element is to be prepared, and on In the case of those elements which the ease of preparation. are required on a commercial scale, like iron, for example, the process of manufacture is regulated chiefly by the cost of the ore, and of the operations necessary to produce the metal in a state of purity sufficient for commercial purposes.
But if perfectly pure iron is required for scientific purposes for example, in order to determine its electrical properties then the question of cost does not come into consideration, and processes are adopted which are necessarily very costly. In the description which follows, however, we shall give only the ordinary methods of preparation. Again, the process chosen depends greatly on the physical and chemical properties of the element which it is desired to Some elements are volatile, and are more or less isolate. easily separated by distillation from the material from which they are produced ; some elements are attacked by water, while others resist attack ; some fuse at comparatively low temperatures, and can thus be separated, while others are producible in a compact state only at the enormously high It is necessary, therefore, to temperature of the electric arc. know the properties of the element required before deciding its isolation. The preparation of the remaining elements will therefore be considered from this point of view.
on a process for
(i)
Separation of the element by means of an
electric current.
(a)
From a
fused salt.
One
condition
is
that
the
fuse at a convenient temperature that is, at or a red heat. Another is that, in the case of metals
salt shall
below which are commercially used, the salts must be cheaply obtainable, and the metals easily separated from the salts. It is interesting to note that this process led, in the hands of Sir Humphry Davy, to the discovery of the metals of the alkalies, potassium and sodium ; he first prepared them by passing a current from a battery of high voltage
MODERN CHEMISTRY
8
through the hydroxide, melted on a piece of platinum foil. The metal was visible only for an instant ; for it floated up from the electrode of platinum wire, and burst into flame as soon as it came into the air. As a rule, however, the chlorides are the most convenient salts for electrolysis. From the known fact that the melting-point of a compound is lowered by the presence
of an "impurity," it is often found advantageous to electrolyse a mixture of chlorides rather than a pure chloride ; in this case one of the elements is liberated in preference to the other. As the anode has to withstand the action of chlorine, it is always made of carbon, which does not unite with chlorine directly ; the kathode may be of iron, a metal which has no tendency to form alloys with those
which are prepared
in this
The kathode required. chloride is kept fused.
The
at least at the temperatures be the iron pot in which the
way,
may
elements which
are prepared in this way are : sodium, potassium, rubidium, caesium, beryllium, The first five magnesium, calcium, strontium, and barium. are easily fusible white soft metals, which take fire when heated in air, and must therefore be kept in an atmosphere lithium,
from oxygen ; they also attack water, liberating hydrogen, with formation of the hydroxide Their density is so low that they float on their fused chlorides ; they must, therefore, be liberated in the interior of a bell-shaped iron electrode or of a fireclay receptacle, down which an iron kathode passes. Beryllium and magnesium are better prepared from a mixture of their chlorides with potassium chloride ; the latter melts and collects at the bottom of the They are pot, which, in this case, may be the kathode. hard white metals, magnesium melting at about 750, and beryllium about 1 200. They, too, take fire when heated in air, and burn with a brilliant flame ; indeed, the chief The metal is use of magnesium is for signalling purposes. drawn, while hot, into wire, which is then rolled into ribbon; this ribbon burns with an exceedingly bright flame, free
MOH.
METALS OF THE ALKALIES
9
oxide MgO. Calcium, strontium, and producing barium are also white metals ; they have been produced by which electrolysis of their cyanides, M(CN) 2 compounds fuse at a lower temperature than the chlorides. They are the
,
very readily attacked by water, yielding the hydroxides The only two of these metals which find 9.
M(OH)
commercial use are sodium and magnesium. Aluminium, which is also manufactured on a large scale, is produced from its ore, bauxite, from which pure alumina, the oxide, is first prepared. The alumina is dissolved in fused cryolite, a fluoride of aluminium and sodium of the formula Na 3 AlF 6 , deposits of which occur in Greenland. The aluminium sinks to the bottom of the crucible, and when a sufficient quantity accumulates it is tapped out.
The " flux,"
as
the cryolite
is
and a further quantity of alumina metal
is
ductile
fairly
is again melted, dissolved in it. The
termed, is
hard, white, susceptible of a high polish,
and malleable.
It
is
also very light (about
two and
a half times as heavy as water), and not easily oxidised in air at the ordinary temperature, nor is it attacked by water.
() From a
dissolved salt. Gallium, a tin-white, very rare, contained in some zinc ores, is deposited from a solution of its hydroxide in caustic potash. Copper prepared, as will be seen below, in a crude state by displacement, is purified by electrolysis. hard
metal,
of the utmost importance to employ pure copper for for although copper ; is one of the best conductors, its resistance is enormously increased by the presence of a very small trace of impurity. To purify it, large rectangular blocks of crude copper are suspended close to thin sheets of pure copper in an acid bath of copper sulphate, CuSO .Aq. The heavy block 4 is made the anode and the thin sheet the cathode ; the It
is
the conduction of electric currents
SO 4 , in discharging at the anode, dissolves copper from the thick block as sulphate; while the cuprion,
sulphation,
++ Cu,
in
yielding up
its
charge
at
the kathode, deposits on
MODERN CHEMISTRY
io
and increases its thickness. The impurities, antimony, and iron, remain in solution, and a sludge is deposited containing silver and gold, besides traces of many other elements. Copper is a very malleable, ductile red metal, melting at 1330. " Objects of iron are often nickel-plated," or covered with a thin film of nickel, a white, hard metal which preserves its lustre in air, for it is not easily oxidisable. This is done by making the object to be coated with nickel the kathode and a bar of nickel the anode; the liquid is a solution Iron objects are first of oxalate of nickel and potassium. Silver and gold are coated with copper before nickelling. best deposited from their double cyanides with potassium ; these salts are used because the deposit is harder and more uniform than if a halide be used. In thus coating objects, it is of importance that the current density, i.e. the ratio of the current to the area of the surface of the object to be coated, should be considered ; if this be too high, the metal will be deposited in a loose, flocculent condition. As an illustration of the changes which take place during such electrolysis, the deposition of silver may be chosen. The compound employed is, as stated, the double cyanide (see p. 187) ; its formula is KAg(CN) 2 , and the ions the
latter
arsenic,
+
are
K
and
Ag(CN) 2
.
There
however,
are,
at the
same
+
Ag
and
deposited on is reduced, a
the
time a few ions of silver
is
amount
CN.
fresh
From
kathode
;
quantity
the
and is
metallic
last,
as soon as its
formed by the
The decomposition of the complex ion, Ag(CN) 9 formation and deposition of the silver ion goes on continuously until all the silver required has been deposited. Similar changes take place during the electro-deposition of .
nickel and of gold.
Modern caustic soda
enormous
electrolytic processes for obtaining chlorine and from salt result in the liberation of
(NaOH)
quantities of hydrogen.
The
salt,
dissolved in
ELECTRO-DEPOSITION
n
placed in a tank divided into two compartments the anode, which consists of ; carbon rods, dips into one, and the kathode, which may be formed of copper plates, in the other. The ions, of water,
is
by a porous diaphragm
+
The chlorine is libercourse, are Na.Aq, and Cl.Aq. ated at the anode, and the sodium at the kathode. But as soon as the sodion is discharged, it reacts with the water, . forming caustic soda, thus : zNa
+ zHOH = iNaOH + H
Hence the production of hydrogen. may be liberated in the same way as
Bromine and iodine
chlorine, the bromide or iodide of sodium or potassium being substituted for the chloride. As fluorine at once acts on water, liberating
oxygen in the form of ozone, O 3 , it cannot be produced from an aqueous solution of a fluoride ; but it has been found that liquid hydrogen fluoride has ionising power, so that on passing a current between poles of platinum-iridium (an alloy of metals which is less attacked by fluorine than any conductor) through a solution of hydrogen- potassium fluoride, HKF, in pure liquid hydrogen fluoride, F 2 , at -30, fluorine is evolved from the anode 2 as a pale yellow gas with a strong characteristic smell, somewhat resembling that of the other halogens, chlorine, bromine, and iodine ; while hydrogen is evolved at the kathode, having been produced by the action of the potassium on the hydrogen fluoride. Fluorine boils at 195, chlorine at 35, bromine at 59, and iodine, which is a solid at atmospheric temperature, melts at 114 and boils at 184. The colours of these elements also show a Chlorine is greenish-yellow; bromine, red both gradation. as gas and liquid ; iodine is a blue-black solid and a violet These three elements are somewhat soluble in water, gas. and more so in a solution of their soluble salts. It has recently been found that another ionising agent than water may be used. Lithium chloride is soluble in pyridine, a compound of the formula C 5 5 N, and may be electrodeposited on a platinum kathode from such a solution. other
H
H
MODERN CHEMISTRY
12
The
metal
however,
is
is
not attacked
by pyridine
;
the
chlorine,
rapidly absorbed.
(2) Separation of an of temperature.
element from a compound
"by rise
This method
is
applied in practice only to the prepara-
and of chlorine, bromine, and iodine ; but many other elements may be thus made, where the compound heated does not tend to re-form on cooling. These
tion of oxygen,
cases will be considered
first.
CH
Ordinary coal-gas consists chiefly of methane, 4, ethylene, C 2 4 , carbon monoxide, CO, and hydrogen, the last amounting to nearly 50 per cent, of the volume This hydrogen owes its origin, at least in of the gas. rt, to the decomposition of its compounds with carbon, y their coming into contact with the red-hot walls of the retort in which the coal is distilled. Carbon deposits in a dense black mass on the iron, and is removed from time to time with a chisel. Hydrogen escapes and mixes with the This form of carbon is used for the pencils for coal-gas. arc-lights, and for the anodes of Bunsen's and other forms of cells, and also for anodes in electro-chemical processes. The compounds of hydrogen with nitrogen (ammonia, sulphur, selenium, and tellurium (sulphuretted, 3 ),
H
NH
H
H
seleniuretted, or telluretted hydrogen, 9 S, 2 Se, H.,Te), all of which are gases at the ordinary temperature, are decomposed if passed through a red-hot tube, giving hydrogen,
which escapes along with nitrogen if ammonia be heated ; or a deposit of the sulphur, &c., in the cold part of the tube if one of the other gases mentioned be employed. The oxides of the metals ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, gold, and mercury are decomposed at a red heat and the chlorides, bromides, iodides, and sulphides are also decomposed, except those of silver and mercury. But none of these methods are practical plans of prepar;
ing the elements.
On
the other hand, as already stated,
DECOMPOSITION BY HEATING
13
method is generally used for the production of oxygen. This gas, although it had probably been obtained in an impure state by the older experimenters, was first produced in approximate purity by Priestley and simultaneously by Scheele in 1774. Priestley produced it by heating mercuric oxide, HgO, which decomposes thus 2HgO = 2Hg + O 2 And Lavoisier showed that it was possible to produce mercuric oxide by heating mercury to its boiling-point in a confined portion of air, and by separating and weighing the oxide, and subsequently heating it till it decomposed again, he proved that the oxygen had really been extracted from the air. this
:
.
Certain oxides are not wholly decomposed into oxygen and element when heated, but leave an oxide containing less
oxygen than that originally heated. Among these is manganese dioxide, a mineral named pyrolusite
black
;
3MnO 2 = Mn g O 4 + O 2 =
.
Lead dioxide undergoes
a similar
O
2PbO 2 2PbO + 2 . The most important application of this method, however, is the commercial plan " of producing oxygen carried out in the " Brin Company's works. In their process, barium oxide, BaO, is heated in iron tubes under pressure, air being pumped in. The barium oxide absorbs the oxygen of the air, the nitrogen After the operation has gone on being allowed to escape. for about five minutes, a considerable amount of oxygen is The absorbed, barium dioxide, BaO 2 , being formed. stopcocks of the pipes leading to the pump are then reversed, so that gas is exhausted from the hot iron tubes. When the pressure is reduced, the barium dioxide loses oxygen, and again returns to the state of monoxide 2BaO 2 = 2 BaO + O 2 . The pumping is continued for about five minutes, and the valves are again reversed. The process is thus a continuous one ; the oxygen is not pure, for it contains about 7 per cent, of nitrogen ; but for medical use in cases of pneumonia, and for the oxy-hydrogen blowchange:
:
pipe,
its
purity
is
sufficient.
This method of preparing oxygen
is
an instance of what
MODERN CHEMISTRY
14 is
termed " mass-action."
The
stant, but the pressure is raised
temperature is kept conit is desired to cause
when
the oxide to absorb oxygen, and lowered when it is necesWhen pressure is raised, the sary to remove the oxygen. number of molecules of oxygen in unit volume of the space {or the mass) is increased, and hence the number in contact with the absorbing medium, the barium oxide. CombinaOn reducing tion, therefore, takes place between the two. pressure, the
number per
unit
volume
reduced, and the
is
The phenomenon
is analogous with the behaviour of a vapour when it is compressed ; the vapour after a certain pressure has been reached the vapour condenses to a liquid, and if more pressure vapour be compressed into the same space, the pressure does not rise further, but more vapour is condensed : this is analogous to the formation of more BaO On pumping 2 out vapour, the pressure does not fall, but the liquid this is the analogue of the decomposition of evaporates The law of mass-action is very the BaO 2 into BaO.
compound decomposes.
.
:
generally applicable. Certain oxides, for instance, pentoxide of iodine, I 2 5 , and of nitrogen, when heated. These 2 & , decompose
O
NO
oxides form combinations with the oxides of many other elements, such as sodium or potassium oxide, e.g. Na 2 O.I 2 5 a similar compound is O.N 2 5 or or NaIO 3 , 3 ; 2 O.CJ 2 5 , although the potassium chlorate, KClO g or 2
O
K
O
KNO
K
O
Now, potassium simple oxide of chlorine is unknown. and sodium oxides are not decomposed by heat, and when these salts are heated oxygen is evolved from the pentoxide These elements, however, do not of chlorine or iodine. escape, but replace the oxygen combined with the sodium forming chloride of the metal, thus O + C1 2 = 2KC1 C1 2 +50, and 2 + O, or, summing up both changes in one equation, 2KC1O 3 = 2KC1 + 3O 2 . Nitrate of potassium, on the other hand, loses only one atom of oxygen, leaving nitrite: 3 or
potassium,
K 2 O.C1 O 5 = K 2 0+ 2
:
K
2KNO
DECOMPOSITION BY HEATING
15
a colourless gas, without smell or taste ; it Oxygen can be liquefied, at a high pressure and a low temperature, Most elements to a pale blue liquid boiling at -182. is
often with such a rise of temperature produced ; in such a case the phenoIn many instances, for termed "combustion."
unite directly with that incandescence
menon
is
it,
is
example when iron rusts, the oxidation is not attended by any measurable rise of temperature, although in all cases heat is evolved, but in some cases extremely slowly. Chlorine, bromine, and iodine are generally prepared by heating together a chloride, bromide, or iodide with manganese dioxide and sulphuric acid diluted with water.
Here
the
hydride,
first
is
change
HC1, HBr,
or
with
the
MnCl 4 Aq,
thus
.
The
-
+
ionised in water, and the reacts
the formation of the halogen
HI.
HCl.Aq.,
hydride, however, for example, at
is
once
MnO 2 forming non-ionised water and MnO 2 + 4 HC1. Aq. = M n C 4 Aq. + ,
:
1
.
2H.2 O.
Tetrad manganese, however, appears not to be able to co-exist with chlorine in solution ; hence the manganese loses an electron
and becomes
Mn,
the lost charge neutralis-
ing one of the charged chlorine ions,
which escapes
in
an
Even then, however, the Mn, though capable of existence at low temperature, still loses a charge, and a second chlorine atom is liberated in a nonelectrically neutral state.
ionised state.
++
Hence
-
the whole change
= MnCl 2 Aq. + Clg.
is
:
Mn
CL.Aq.
these changes in one
Summing we have: MnO 2 + aNaCl.Aq. + 2H 2 SO 4 .Aq. = MnSO 4 Aq. + Na 2 SO 4 Aq. + 2H 2 O + C1 2 or, if hydrochloric acid alone be warmed with manganese dioxide, MnO 2 + 4 HC1. Aq. - MnCl 2 Aq. all
.
equation,"
.
.
;
.
of an element from a compound by ( 3 ) Separation This is by far the most general method displacement.
MODERN CHEMISTRY
16
The
of preparing elements. displacing agents are :
elements
commonly used
as
The oxide or chloride (a) Hydrogen at a red heat. placed in a tube of hard glass, heated to 600 or 700 in a tube-furnace, and a stream of dry hydrogen is passed Water or hydrogen chloride is formed, through the tube. is
and is carried on by the current of hydrogen, and the element i-s left. Indium, thallium, germanium, tin, lead, antimony, and bismuth are left in fused globules, solidifying to white lustrous metallic beads ; arsenic gasifies and condenses in the unheated part of the tube as a grey deposit ;
tellurium, which is also volatile, condenses as a lustrous metallic solid ; while iron, cobalt, nickel, copper, and silver do not fuse at that temperature. The first three remain as
grey powders, the copper as a red powder, and the silver These metals can be fused white spongy condition. by heating them in a crucible to a sufficiently high tem" flux," or substance to make perature ; it is well to use a them flow, such as sodium carbonate or borax ; the flux fuses, and dissolves any film of oxide off the surface of the metallic beads, and they then join up to form a single mass in a
of molten metal. (b)
Displacement by means of sodium at a red
The chlorides of beryllium, magnesium, calcium, strontium, barium, aluminium, scandium, yttrium, lantha-
heat.
num, ytterbium, cerium, thorium, vanadium, niobium, and tantalum are all reduced when added to sodium kept melted in an iron crucible. For boron, silicon, and titanium the double fluoride
is
more convenient,
for
the chlorides are
The
process for manufacturing magnesium, which is carried out on a large scale, may be more The double chloride minutely described as an example. volatile
liquids.
of magnesium and potassium, MgCl 2 KC1, carefully dried, is mixed with sodium in proportion to unite with the chlorine of the MgCl 2 the sodium being in small lumps. The iron crucible containing the mixture is heated ; a .
,
violent reaction takes place,
and magnesium
is
liberated
:
DISPLACEMENT MgCl 2 KC1 + zNa = .
is
volatile,
operation.
Mg + 2NaCl + KC1.
and can be
The
distilled,
it
is
17
As magnesium purified
by
this
contents of the crucible are treated with
water ; the potassium and sodium chlorides dissolve, and the globules of magnesium are collected, dried, and placed in a crucible, through the bottom of which a tube is fixed reaching nearly to the lid, and projecting some distance This crucible is placed in a furnace, below the bottom. and on raising the temperature, the magnesium volatilises the up, passes down the tube, and the vapour condenses in cooler part of the tube which projects below the furnace. This particular method of distillation is called dcstillat'w per
The
descensum.
other elements mentioned are too
to admit of purificaiion
little
In their case, the cooled mass is treated with alcohol in order to remove the excess of sodium, and then with water to dissolve the resulting salt ; the element is left in the state of powder. (c) Displacement by means of magnesium at a red This process is sometimes used to prepare the heat. element from its oxide. mixture is made of magnesium filings with the oxide of the element, and it is heated in an iron crucible. The resulting mass is then treated with hydrochloric acid to remove the oxide of magnesium, which is thus converted into the soluble chloride. It is, of course, essential that the liberated element shall not be attacked by volatile
by
this
means.
A
The process works for the preparation hydrochloric acid. of boron, silicon, and titanium. (d} Displacement by heating the oxide with carThis process is of the most general application. bon. If the element is volatile, it is distilled from an iron or fireclay
retort
;
in
this
way sodium,
potassium,
rubidium,
and cadmium are prepared. If non-volatile at a red heat, a mixture of the oxide with charcoal is heated to bright redness in a clay crucible. On a manufacturing scale, coal or coke is substituted for the charcoal.
arsenic, zinc,
The
process VOL. II.
is
applicable
to
the production of indium, B
MODERN CHEMISTRY
i8
thallium,
germanium,
tin,
To
nickel, and copper. instances will be described
sodium, zinc, and
Phosphorus. are
phosphorus
manganese, iron, cobalt, this method, four the preparation of phosphorus,
lead,
exemplify
iron.
The commonest or
phosphorite
natural
compounds of
calcium
phosphate,
and gibbsite or aluminium phosphate, A1PO 4 It is accordingly convenient and economical to prepare The process depends on phosphorus from one of them. the displacing action of carbon on the oxide at a high There are two methods of effecting this. temperature. The first is the phosphorite is mixed with dilute sulphuric acid ; the hydrogen of the sulphuric acid replaces the calcium of the calcium phosphate: Ca 3 (PO 4 ).,+ 3H 2 SO 4 .Aq
Ca 3 (PO 4 )
.
,
:
= jCaSO 4 + 2H g PO 4 .Aq.
Coke
or charcoal
is
impreg-
nated with the phosphoric acid and heated to redness, = the phosphoric acid loses water 4 3 3 + :
The
H PO
when
HPO H O. HPO with carbon 2
mixture of metaphosphoric acid, 3, is charged into retorts of Stourbridge clay, the mouths of which are attached to a vertical copper tube, the lower On raising the retorts to end of which dips under water. a white heat, phosphorus distils over and condenses in the
The final equation is 4HPO 3 + 1 2C = 2H 2 + P 4 By the second method, the calcium and alumi-
water.
:
+ I2CO.
nium phosphates are mixed with silica and carbon, and from an electric furnace heated to whiteness by
distilled
an arc
in its interior.
A
mixture is made of "spongy iron" (see This mixture is heated to redness in and pitch. p. 19) order to decompose the pitch, which consists of compounds These compounds are decomof carbon and hydrogen. posed, and a part of the carbon is left mixed with the
Sodium.
spongy iron, while the hydrogen escapes in combination To this mixture, placed in with the rest of the carbon. the lid of the an iron crucible, caustic soda is added crucible, which is furnished with a curved tube sloping downwards to a condenser, is fixed in place, and the ;
ZINC AND IRON
19
a furnace to bright redness.
The
crucible is heated in carbon removes oxygen both from the hydrogen and the sodium, and sodium and hydrogen pass over into the condenser along with carbon monoxide, the sodium alone The condensing, for the others are gaseous and escape. = 2CO + 2 + 2Na. The conequation is: aNaOH + 2C
H
denser consists of a flat hollow copper vessel is raked out as it accumulates. Zinc. convert
The it
chief ore of zinc
into the oxide,
current of air
:
2ZnS +
it is
30.,
is
the
roasted on a
;
the sodium
sulphide. flat
= 2ZnO + 2SO 2
.
To
hearth in a
The
oxide
mixed with small coal (black) and placed in cylindrical These retorts have pipes of rolled retorts of fireclay. is
sheet-iron luted to the open ends with fireclay ; they are packed into a furnace in tiers, and the temperature is raised The coal distils first, giving off coalto bright redness. gas,
which expels
perature exceeds the iron pipes.
air
from the
1000,
retorts.
When
the
tem-
the zinc distils and condenses in
happens that almost all zinc ores which, like zinc sulphide, is converted into oxide by roasting ; and on distillation, the cadmium, which is the more volatile metal, distils over first and condenses in the outer portion of the tubes. These are untwisted and the metal removed with a chisel. The chief ores of iron are the carbonate and Iron. the oxide. The former is practically always mixed with clay (clayband) or with coal (blackband), and generally contains sulphur and phosphorus in the form of calcium sulphate, CaSO 4 , and calcium phosphate, Ca 3 (PO 4 ) . The sulphur is sometimes present in the form of iron The ore is roasted to expel carbon pyrites, FeS . If it dioxide, thus": 4 FeCO 3 + O 2 = 2Fe 2 3 + 4 2 were then in its impure state smelted with coal, the iron would not flow, but would remain mixed with the However, this process, if the ore is pure and charcoal clay. is used as fuel, yields a mass of iron sponge, which can be heated and welded by hammering into a coherent mass. contain
cadmium
It
sulphide,
O
CO
.
MODERN CHEMISTRY
20
The
used by Africans, and was at one time the large scale, however, it is necessary to add lime in order to form a flux with the clay. Clay conprocess
universal.
is
still
On
sists of a compound of silica, SiO , and alumina, A1 2 O 3 and with lime it melts to a glassy slag. Alternate layers of coal, lime, and the roasted ore are fed in at the top of a blast-furnace, a tall conical erection of firebrick, strengthened by being bound with iron hoops ; at the bottom there " crucible," or is a receptacle for the molten iron, which ,
can be discharged when required by forcing a hole in its There are also holes which admit side with an iron bar. water-jacketed tubes or "tuyeres," which convey a blast of air heated to about 600 to increase the temperature of Here the reduction takes place combustion of the coal. in the upper part of the furnace, owing to the carbon monoxide formed by the combustion of the coal in the lower part of the heated mass ; it acis on the oxide of iron As the iron passes thus: Fe 2 3 + 3CO = 2Fe + 3CO 2 down the furnace it melts, and is met by the fused slag ; it then coheres and runs into the crucible, whence it is drawn off from time to time. Carbon unites with molten iron, forming a carbide ; hence
O
.
the product of the blast-furnace is not pure iron, but a mixture of iron with its carbide, and also with its sulphide and phosphide, if the ore has contained sulphates or phos-
When such impure iron is brought in contact with oxygen in a molten or semi-molten condition, the carbon, sulphur, and phosphorus are oxidised mostly before If lime be present, sulphate and phosphate of the iron. The modern process of removing calcium are formed. these impurities is to pour the molten metal into a pearshaped iron vessel lined with bricks made of magnesia; phates.
while it is molten, air is blown through the metal, and the carbon burns to carbon dioxide ; the sulphur and phosphorus are likewise oxidised and combine with lime, a layer of which floats on the surface of the molten metal. When " Bessemer these impurities have thus been removed in the
DISPLACEMENT BY OXYGEN
21
Steel is the metal is poured into a mould. mixture of iron with a trace of its carbide, and it is produced by mixing with the blown iron, before it is and manganese poured, a quantity of iron containing carbon
converter," a
which confers valuable properties on iron). The (a metal quantity of carbon in steel may vary between 0.6 and 1.5 the quality per cent. ; with the content of carbon varies also of the
steel
;
that with
a
small proportion
is
soft,
with
a high proportion hard.
Displacement by means of Oxygen. Oxygen in Deacon's process to liberate chlorine from The latter gas, mixed with air, is hydrogen chloride. a chamber through kept between the limits of passed (e)
is
used
temperature 37 5 "-400, containing bricks soaked with At this temperature the cupric cupric chloride, CuCl . chloride decomposes into cuprous chloride, CuCl, and free chlorine, but the cuprous chloride is reconverted into cupric chloride at the expense of the chlorine produced
by the interaction of the hydrogen chloride and the air, thus The cupric chloride is 4 HC1 + O 2 - 2H 2 O + 2C1 2 This kind of action, where a limited again decomposed. :
.
quantity of a substance, itself not permanently changed, causes an apparently unlimited change in other reacting " surface action," for its rate is dependent bodies, is termed on the extent of the surface of the agent ; and the name
"
**
catalysis
action
is
sometimes given to such an action.
would take place independently of the
The
catalytic
agent, but at a very slow rate
; the presence of the catalyser has the effect of greatly increasing the rate at which the The chlorine thus prepared is not change takes place.
pure, but mixed with the nitrogen and argon of the air, but it serves for some purposes. The rate of such action of oxygen in displacing bromine or iodine from their
compounds with hydrogen
is
much
greater,
and
at a
high
temperature the elements could be formed thus, but they are not usually produced in this way.
The
preparation of nitrogen
may
be also regarded as a
MODERN CHEMISTRY
22
Ammonia burns in displacement by means of oxygen. = sH 9 + 9 , but at the oxygen, thus: g + 3O same time some of the nitrogen unites with the oxygen and forms , nitric peroxide : this gas interacts with the
O N
3NH
NO
NH NO
ammonia, forming ammonium nitrate and nitrite, and NO If, however, the oxygen be not 4
NH
in it
.
4
3
free, but
combination with an easily reduced metal, such as copper, combine with the hydrogen of the ammonia at a red
will
heat, setting free the nitrogen.
Another method involves
mutual displacement of nitrogen from its oxide by means of hydrogen, and from its hydride, ammonia, by
the
N
2NH 3 + 2 O 3 = 3H 2 O + 2N 2 This method is, = however, usually represented by the equation 4 2 be 2H.,O + 2 ; for ammonium nitrite, , 9 may 4 O 3 with 2NH 3 and 2 O. regarded as a compound of 2
oxygen:
.
NH NO NH NO H
N
N
To is
be
obtain nitrogen by this method, since ammonium nitrite not easily obtained, a solution of ammonium chloride may
warmed with one of sodium
then
:
nitrite.
The
equation
is
NaNO 2 Aq + NH 4 C1. Aq = 2H 2 O + N 2 + NaCl. Aq. .
Another convenient method is to warm together solusodium hypobromite and ammonium chloride the former loses oxygen readily, which combines with the hydrogen of the ammonia according to the equation
tions of
;
:
3NaOBr.Aq. + 2NH 4 CJ.Aq. = 3NaBr.Aq. + 3H O + 2HCl.Aq. + N 2 .
Although
sulphur, selenium, and tellurium burn in
oxy-
H
gen, still they may be displaced from their hydrides, 2 S, and means of oxygen at a red heat, 2 Se, 2 Te, by provided the oxygen is present only in sufficient quantity to
H
H
=2H
O+ combine with the hydrogen, thus 2H 2 S + O 2 2 S 9. Aqueous solutions of these compounds, too, are decomposed on standing in contact with air, owing to similar displacement. Oxygen may displace mercury from its sulphide, cinnabar, HgS, which is the common ore of :
here the sulphide is roasted in air, when the ; sulphur combines with the oxygen to form sulphur dioxide, a gas at ordinary temperature ; and mercury is liberated,
mercury
DISPLACEMENT OF ELEMENTS also
23
the gaseous form, but condensing at temperatures
in
below 358.
(/) Displacement by use of Fluorine, Chlorine, and Bromine. Fluorine, chlorine, and bromine may also be as displacing agents for nitrogen and oxygen. employed
A
current of fluorine led through water displaces the oxygen, forming hydrogen fluoride ; but the oxygen is in an allotropic state (see Part i.), called "ozone." Again, if a stream of chlorine is passed through, or if brominewater be added to, a solution of ammonia, the hydrogen and chlorine combine, while the nitrogen is set free:
N
but as ammonia com3C1 2 = 6HC1 + 2 hydrogen chloride, the reaction 6NH 3 + 6HC1 = 6NH 4 C1 occurs simultaneously; the complete equation is the sum of these two: 8NH 3 .Aq+ 3d 2 = 6NH 4 Cl.Aq
2NH 3 .Aq +
;
bines with
+ N2
.
Chlorine, added to a solution of bromide or iodide of a metal, displaces the bromine or iodine ; here the nonionised chlorine becomes ionised at the expense of the charge on the ionised bromine or iodine, while the latter
+ lose their charges, thus
:
-
+
2KBr. Aq + C1 2 Aq. .
-
= aKCJ.Aq
+ Br.,. Aq.
Similarly, bromine displaces iodine from a But iodine displaces chlorine from the iodide.
soluble
Here, the iodine is still nearly insoluble silver chloride. than the chloride ; and as chloride dissolves,
less soluble
the less soluble and therefore non-ionised iodide
is
formed.
metals are able to displace others. Thus, iron placed in a solution of a copper salt displaces the In all copper displaces silver ; silver, gold. copper these cases the action is doubtless an electrical one, and (g)
Many ;
dependent on the replacement of a metal of lower by one of higher electric potential ; that of higher potential becomes ionised, while that of lower assumes the metallic state, thus:
CuCl,.Aq+Fe=FeCl 2 .Aq + Cu; 2AgNO 3 .Aq-f
Cu = Cu(N0 3 ) 2 .Aq + 2Ag.
MODERN CHEMISTRY
24
There are some plans of obtaining elements which, (/>) though they can be referred to one or other of the three general methods exemplified already, are, on account of their complexity, better treated separately.
Among
these
methods of separating hydrogen. The metals of the alkalies and alkaline earths attack water, forming hydroxides and liberating hydrogen 2Na + 2H.7 O = zNaOH + are the
:
H
2
;
Ca +
2H ,O = Ca(OH) + H 2 L
2
.
Magnesium powder,
boiled with
but zinc water, gives off hydrogen slowly requires the presence of an acid, and must not be pure, i.e. there must be a foreign metal present to serve as the The impurity usually present in commercial zinc anode. is
lead
;
;
the acid, for instance, sulphuric acid,
+ +
dilute solution as ions of
HH
and
SO 4
;
the
is
present in
SO 4
removes
++ the surface layer of the zinc as Zn, while the negative charge is transferred to the lead, which is in metallic This charge is neutralised by the contact with the zinc. + +
HH,
which, on being discharged, It may then be collected escapes in an non-ionised state. over water, in which it is very sparingly soluble. Hydrogen, while it is on the point of discharging and is still in the ionised state, may be used to liberate certain elements from
positive charge of the
Zinc and hydrochloric acid, ++for instance, in a solution of stannous chloride, SnCl .Aq, causes a deposition of tin owing to the exchange of charge the hydrogen retaining its charge instead of parting with it their
oxides or chlorides.
;
to the lead or other impurity in the zinc, while the tin is If zinc and hydrochloric acid are discharged in its stead.
placed in contact with silver chloride, AgCl, which is an insoluble compound, the hydrogen remains charged, while the silver parts with the chlorine, the latter remaining in solution with negative charge. Lastly, if generated in a solution of ferric chloride, Fe Cl 3 .Aq, the zinc goes into solution as before ; and the positive electricity is provided
PROPERTIES OF ELEMENTS
25
by the loss of a positive charge provided by the ferric ions
++
-
changing to the ferrous ions of ferrous chloride, FeCl 9 .Aq, -
+
The and another molecule of HCl.Aq exists in solution. Such processes are genevalency of the iron is lowered. rally termed reduction ; the hydrogen is said to be in the " nascent ** state," and is named the reducing agent." Metallic iron, manganese, cobalt, and nickel at a red heat remove oxygen from water with liberation of hydrogen
3Fe + 4 H 2 O-Fe 3 O 4 +3H 2
:
+ O2
2Co + 2H 2 O = CoO
;
Conversely, a current of hydrogen passed over these oxides at a red heat will combine with their oxygen, .
This is an instance of massreducing them to metal. From the equations given above, it is seen that hydrogen is formed ; it does not remain in the tube to
action.
re-form water or
;
equilibrium,
if it all
did, there would be a state of balance four substances remaining together in
proportions depending on the temperature and on their nature ; in the current of steam, however, the hydrogen is carried on, and is no longer present to act on the oxide of
And in the converse action the hydrogen conveys the steam away, so that it can no longer be deprived of oxygen by the metal. As already remarked, carbon monoxide has a similar reducing action on the oxides of the more easily reducible the metal.
elements. for
The
example,
product in
requires a red heat.
may be
+ KCNO.
As
3CO 2
.
CO.2
,
This action
Another reducing agent, applied by is potassium cyanide, KCN
fusing the oxide with it, it is converted into the
thallium
this case is the dioxide,
Fe 2 O 3 + 3CO = zFe +
;
cyanate,
KCNO.
O
The
metal
KCN = 2T1
+ prepared by its help, T1 9 the cyanide is somewhat expensive,
it is
used only in special cases. An instance has already been given of the mutual reduction of two compounds in the case of nitrogen. Similar instances are
lead and with sulphur. The the sulphide, a natural product termed
known with
chief ore of lead
is
MODERN CHEMISTRY
26 It
galena.
red heat.
is roasted, i.e. heated in contact with air to a After a portion has been oxidised to sulphate,
PbS-f 2O 2 = PbSO 4 sulphide and
,
the temperature
is
raised,
when
the
sulphate mutually reduce
each other : With sulphur the partial PbS + PbSO 4 =2Pb + 2SO 2 . burning of sulphuretted hydrogen may be explained in a S + 2 = 2H 2 + S 2 , similar manner ; the reaction, 2 may be represented as the formation of water and sulphur the
2H
O
O
dioxide by the complete combustion of one-half of the hydrogen sulphide, and its reaction with the remaining
S + SO 2 = thus: + 38. And, as a 2 2 matter of fact, that reaction does take place on mixing the two gases in the required proportion of two volumes of hydrogen sulphide with one of sulphur dioxide. sulphide,
2H
2H O
The Properties of the Elements. to divide the elements into
tomary and the non-metals. is
As we
a completely arbitrary one
;
two
It has
been cus-
classes, the metals
have seen, this classification for there are some elements
The name "metal" capable of existing in both states. was originally given to seven substances, all alike in possessThese were ing that bright lustre known as "metallic." But in gold, silver, mercury, copper, iron, lead, and tin. the Middle Ages bismuth and antimony were isolated in a pure state, and these, together with zinc, were at first not received into the class, but were regarded as spurious ; fairly
were brittle and easily oxidisable. Although no reason for retaining the division, yet it is often Bodies which possess metallic lustre have the convenient. for
they
there
is
power of conducting electricity better than transparent bodies, and they are also relatively good conductors of heat.
The
Those elements exist in various physical states. are gases at the ordinary temperature, however, have all been condensed to the liquid state by sufficient reduction which
of temperature. The lowering of temperature is most easily produced by means of liquid air, now a cheap commodity. To liquefy air, it is compressed by a pump to a pressure of 1 50 atmospheres ; it then traverses a coil of copper pipe,
PROPERTIES OF ELEMENTS
27
and escapes from an orifice at the lower end. Now, compressed air has some resemblance to a liquid, for when it expands, as when a liquid changes to gas, heat is absorbed. The rapidly escaping air becomes cold, and in passing up over the coil of tube through which it has descended, it cools the pipe, so that the air passing down
becomes colder and colder ; finally, it is so cooled that it It and escapes from the orifice in a liquid state. may be poured from one vessel to another, with little loss by evaporation ; and if other gases be allowed to stream
liquefies,
The they too are liquefied. is the same, for its boilingit cannot be liquefied by the aid of That of helium is still lower, but it too has liquid air. yielded when compressed into a tube cooled by liquid into a tube cooled
by
principle of liquefying point lies so low that
its
aid,
hydrogen
hydrogen. The elements which are gases at the ordinary temperature are hydrogen, helium, neon, argon, krypton, xenon, nitroThe first gen, oxygen and ozone, fluorine, and chlorine. seven are colourless, both in the gaseous and the liquid state. Oxygen is a colourless gas, but forms a pale blue liquid ; gaseous ozone has a blue colour ; fluorine is pale It yellow ; and chlorine has a greenish-yellow colour. forms a white solid, which, however, melts to a bright Bromine is a dark red liquid at atmospheric green liquid. temperature, but above its boiling-point, 59, it is a deep red gas. Iodine is a blue-black solid, melting to a black
114, and giving off a violet vapour. Ozone and halogens," as fluorine, chlorine, bromine, and iodine are called, have all a powerful odour, and act on the skin in a corrosive manner. Chlorine and bromine are soluble liquid at
the
"
in water.
the other non-metallic elements are boron, a powder ; carbon, in its ordinary form an amorphous (i.e. non-crystalline) black substance, of which the most familiar variety is charcoal ; carbon does not fuse,
Among
black, dusty, infusible
but at the enormously high temperature of the electric arc
MODERN CHEMISTRY
28 it
volatilises
;
silicon, a
blackish-brown powder, melting
at
bright redness to a lustrous liquid, which solidifies in shining black lumps ; phosphorus, a waxy, pale yellow solid, melt; sulphur and selenium, yellow and brown-red former melting at 115 to a brown liquid, and boiling at 446 ; the latter forming a black liquid at 217, and a black vapour at 665. The metals of the alkalies, as they are usually called,
ing at 44.4 solids, the
lithium, sodium, potassium, rubidium,
white metals,
at
and caesium, are
soft
once attacked by water, and oxidised
by air, caesium, indeed, taking fire spontaneously. under protect them from oxidation, they must be kept rock-oil or ligroin, a compound which contains no oxygen. Of these, cassium has the lowest and lithium the highest
readily
To
melting-point. are sometimes
They
The
metals calcium, strontium, and barium alkaline earths."
named the " metals of the
are hard white bodies, also, like those of the sodium
group, oxidising readily on exposure to air, and at once attacked by water. Magnesium, zinc, and cadmium are
noteworthy, inasmuch as their temperature of ebullition is not so high that it cannot be reached in an ordinary furnace; Magnesium and zinc are they can therefore be distilled. hard and brittle ; cadmium is softish, like lead, and of a
somewhat greyer
tint.
The
remaining elements may be classed under the head" hard," " soft," " brittle," &c. This ings, implies only their behaviour at ordinary temperatures ; at higher or lower temperatures the properties are materially changed. Mercury, for example, below -40, is malleable ; lead is brittle.
(a) Malleable metals beryllium, alumi(1) White , ductile, moderately hard: Red, copper. nium, gallium, indium, tin, silver, nickel. :
Tellovu , gold.
(2) Grey-white, manganese, cobalt.
ductile,
and moderately hard:
iron,
METALS (3) Grey-white and soft ; what harder, and fusible only
ductile:
at
29 thallium, lead; some-
a very high temperature
:
raodium, ruthenium, palladium, platinum, iridium. I mercury. Liquid metal : ( ) (c] Brittle metals :
antimony, bismuth, tellurium, zirco(1) White, hard: Less nium, didymium (a mixture), osmium, germanium. hard, arsenic.
Grey, hard:
(2) (
3
nisher
lanthanum, cerium, yttrium, uranium. metallic lustre under the bur-
Grey powders, acquiring
)
thorium, niobium, tungsten. Black powders : tantalum, titanium, 'he elements scandium, samarium, and gadolinium have The not been prepared. :
Although the external properties of the elements does show any obvious relation to their order in the periodic table (see Part I.), yet it may be generally remarked that the density increases as each column is descended. Among not
the lightest of the elements are lithium, beryllium, magnesium, and aluminium, at least in the solid state ; whereas osmium, iridium, platinum,
and gold are among the
much more must be
heaviest.
But
ascertained regarding their properties
before a satisfactory comparison can be made.
CHAPTER Classification of Classification of elements
may be
II
Compounds
The Hydrides. Compounds of
Compounds.
divided conveniently into six classes
the
:
The Hydrides The Halides The Oxides and Sulphides ;
;
(with Selenides and Tellurides) Nitrides and Phosphides (with Arsenides and ;
The
Antimonides)
The The
;
Borides, Carbides, and Silicides Alloys.
;
Compounds can be prepared by many methods it is not so easy to classify them as it is to arrange into classes the methods of preparation of elements. As a rule, the pre;
paration
(a) (b) (c)
(d) (*)
is
carried out by one of the following
methods
:
The interaction of elements The action of an element on a compound The action of heat on a compound The interaction of compounds The addition of one compound to another. ;
;
;
;
These methods
shall be considered in relation to each of the groups of compounds named above.
The Hydrides. (a ) The Interaction of Elements. and potassium, when heated to 300
Lithium, sodium, in
an iron tube
in a
INTERACTION OF ELEMENTS
31
current of hydrogen, form white waxy compounds ; that of lithium has the formula LiH ; as the sodium compound has the formula Na 9 H, its existence is difficult to reconcile with
the usual valency of either hydrogen or sodium, for these elements in all other compounds behave as monads. It would at
It decomposes 421. repay further investigation. Iron, nickel, palladium, and platinum, when heated the gas. Meteoric iron, indeed, gently in hydrogen, absorb
has been
known
to give off,
on heating, 2.85 times
its
This natural variety of iron contains about gas. cent, of nickel. Palladium, gently warmed in an
volume of
6 per atmosphere of hydrogen, absorbs over 900 times its volume of that gas, corresponding to 4.68 per cent, of the weight It is difficult to determine whether of the body produced. or not the palladium is in chemical combination with the hydrogen, or whether the hydrogen is in a state analogous to solution, for it is known that a solid can exert solvent There is a considerable rise of temperature accompower. and if palladium, in a state of panying the absorption sponge, is placed in contact with a mixture of oxygen and therhydrogen, the mixture may be made to explode. mometer-bulb coated with palladium sponge is a good test for the presence of an explosive mixture of marsh-gas and air in mines, for the rise of temperature produced is an inThese metals absorb hydrogen more dication of danger. readily if they are made the negative electrodes of a battery with which dilute sulphuric acid is electrolysed. Iron shows a very curious behaviour under these circumIf a thin plate of iron is made to close the top of stances. a barometer -tube full of mercury and a small cell be constructed on it, hydrogen will pass through the iron, when the plate is made the kathode, and will depress the mer;
A
cury in the tube.
shows
this
No
peculiarity
in the ionic state
;
other metal, so far as is known, it would appear that the hydrogen
can penetrate the iron.
Carbon, heated to 1200 in an atmosphere of hydrogen, unites with it to form marsh-gas Only (methane), CH 4 .
MODERN CHEMISTRY
32
a small percentage of the hydrogen, however, enters into combination ; a balance soon establishes itself between the
number of molecules of methane being formed and decom-
At a higher temperature, that of the is formed, owing to acetylene, C 2 2 the decomposition of the methane into that gas and free 2CH 4 = C 9 2 + 3H 2 Other compounds of hydrogen: carbon and hydrogen are formed simultaneously, and there again appears to be a state of equilibrium produced between With nitrogen, the various hydrocarbons formed. S, it appears to be impossible to induce hydrogen to enter into direct combination at such temperatures but if electric sparks be passed through a mixture of hydrogen and nitroShould the gen, combination to a limited extent ensues. be removed by having water, or, better, ammonia, 3, dilute sulphuric acid, present, the combination proceeds posed
in unit time.
electric
H
arc,
,
H
.
NH
;
NH
until all
the gases, if they were originally present in the
one volume of nitrogen to two volumes of hydrogen have combined. Conversely, if sparks be passed through ammonia gas, there is nearly, but not quite, This enables complete decomposition into its constituents. the volume relations of ammonia to be demonstrated ; for it is found that two volumes of ammonia gas can be decomposed into two volumes of nitrogen and six volumes of correct proportion
hydrogen.
This
is
symbolised by the equation 2
NH
Weight 2(14 +
3
3)
Volume 2(22.4)
=
N + 3H 2
28 22 -4
2
3(2) grams. 3( 22 '4) litres.
The hydrogen
can be nearly completely removed by absorption with palladium-sponge, and the nitrogen remains.
H
is more Water, completely formed than any one 2 0, of the previously mentioned compounds by the interaction of its elements. mixture of oxygen and hydrogen, in the proportion of one volume of oxygen to two of hydrogen, is exploded by heat ; this is most easily done by passing an electric spark through the mixture. While the position of
A
COMBINATION OF HYDROGEN
33
mixture of nitrogen, hydrogen, and amsuch a point that very little of the compound
equilibrium for a
monia
lies at
the uncombined gases, the contrary is present, but chiefly Here nearly all the the case with hydrogen and oxygen. is
oxygen and hydrogen combine, and only a trace remains Combination may be made to take place uncombined. even at 300 slow slowly at much lower temperatures Colloidal platinum, prepared by makcombination occurs. ing an electric arc between poles of platinum under pure water, which appears to consist of very finely divided platinum disseminated through the water, has the power of causing union of oxygen and hydrogen left standing in contact with it, even at the temperature of the atmosphere. On the other hand, if water-vapour be raised to a very high temperature, above 1800, decomposition into its constiso that it is tuents takes place with considerable rapidity possible to obtain a mixture of oxygen and hydrogen by passing steam through a tube in which a spiral of platinum wire is kept at a white heat by means of an electric current. These actions are therefore termed " reversible," and they are expressed by such equations as ;
;
CH.
;C + zH
2
;
zH.,
+ 0,-
2H 20;
Hydrogen also combines with sulphur when passed through a flask containing boiling sulphur, and sulphuretted hydrogen, decomposes when raised to a low red 2 S,
H
heat.
Interesting relations are to be seen with the compounds of the halogens with hydrogen. In preparing fluorine by
the electrolysis of hydrogen-potassium fluoride,
H
KHF,
in
F 2 , it is possible, by stoppresence of hydrogen fluoride, 2 ping the exit of the hydrogen, to cause a bubble to pass the bend of the U-tube and to
rise into
the fluorine
;
the instant
This shows form H 2 F 2 Chlorine and hydrogen, on the other hand, do not com-
the gases unite there is a sharp explosion. that these gases unite even in the dark to VOL.
II.
.
C
MODERN CHEMISTRY
34
bine in the dark, but, when exposed to diffused daylight, slow but complete combination ensues ; in bright sunlight, or when illumined by the light from burning magnesium,
HC1. Bromine and hydrogen unite to form HBr when a current of hydrogen, having bubbled through a wash-bottle of bromine, passes through a red-hot tube ; with excess of hydrogen the union is Iodine and hydrogen, on the practically complete. contrary, unite very incompletely to produce HI ; and if the mixture of gases explodes, forming
hydrogen iodide be heated, a large proportion of it is decomposed into hydrogen and iodine. This change has been investigated much more completely than other changes and as it is of the same character already mentioned ;
characteristic of
all
such reversible reactions,
we
shall
con-
somewhat greater detail. The rate at which hydrogen iodide is produced from a mixture of hydrogen and iodine at any constant temperature is much more rapid than that at which the reverse sider
it
in
change of hydrogen iodide into iodine and hydrogen takes This rate was not difficult to determine. Weighed quantities of iodine were placed in a tube filled with hydrogen, and after heating the sealed tube for a sufficiently long time for equilibrium to be established, it was opened under The hydrogen iodide formed at once dissolved in water. The the water, and the residual hydrogen was measured. amount of uncombined iodine remaining in the water was
place.
It was thus possible then estimated by known processes. to find the ratio of the combined to the uncombined hydroNow, it was discovered many years ago that the rate gen. of chemical change depends on the amount of each of the
a condition exreacting substances present in unit volume Thus, if we double pressed by the term "active mass."
the amount of hydrogen in the mixture of the gases
men-
double its " active mass." Let /, denote the number of molecules in unit volume of the iodine gas, and ^ 2 that of the hydrogen, and let ^hi be that of the hydrogen iodide formed by their interaction. Then, as the rate of tioned,
we
HYDRIDES OF CARBON
35
formation of hydrogen iodide is proportional both to to their product, h x />, it will be proportional /'.
+ I = zHI,
HI
H
/
and to
And
as
into and I 2 the rate of change of 2 2 If we call the rate of formawill be 2/)i x ihi or 4(^/) . tion >, and that of decomposition k' y the proportion of 2 these rates to each other will be kjk' = (h x *)/4(2>/) , if the
H.,
'
At the temone atmosphere pressure, it was found that, taking the total hydrogen as unity, 0.28 was free and 0.72 combined, after a sufficient time had been algases are present in molecular proportions.
perature
440, and
at
lowed for the change to complete itself. Now, the iodine free must have been equal in number of molecules to the free hydrogen, i.e. 0.28, and the same number of atoms of iodine must have existed in combination as of hydrogen in combination; hence 0.28x0.28/4(0.72x0.72) = 0.0375 = /^'. This means that at 440 molecules of hydrogen iodide decompose into hydrogen and iodine at a rate only 0.0375 (or one twenty-sixth) of that at which combination takes place between the two gases. The action of an element on a compound leads (If) This process has been to the formation of many hydrides. of pretty fully treated in the description of the methods For example, on passing a current preparation of elements. of hydrogen over hot cupric oxide, water, H.,0, is formed, = while the oxide is reduced to copper, CuO + 2 Cu + 2 O. The oxides mentioned on p. 16 are thus It is not so usual for sulphides to lose sulphur on reduced. heating them in a stream of hydrogen ; indeed, it is only those sulphides which themselves decompose when heated that yield to such treatment ; but hydrogen fluoride, chloride, bromide, and iodide are formed on heating the halides The process, of many metals in a current of hydrogen. however, is not one which is used for the preparation of
H
H
these hydrides. (c) The third
method that of heating a compound means of preparing hydrides, but
is
also not in use as a
is
often
employed
in
order to produce the
it
compound from
MODERN CHEMISTRY
36
which the hydride is separated. containing water of crystallisation,
Thus,
when
all
compounds
heated, lose water
when raised to a high temperature and double compounds of ammonia, too, lose ammonia on rise of temperature. Such compounds as calcium chloride, CaCl crystallise with ;
,
The
formula of the hydrated compound is CaCl 9 . a similar compound with ammonia, CaCl.,.6NH 3 ,
water.
6H 9 O
;
known compounds like these lose water or ammonia when heated. By this plan Faraday succeeded in liquefying ammonia, which at ordinary temperatures is a gas. Having sealed up the ammonio-chloride of calcium or of silver, AgCl.NH 3 in an inverted U-tube, one leg was cooled with a freezing mixture, while the other was heated, and the gas liquefied under the combined influence of cold and pressure. (d) Most of the hydrides can be prepared by the fourth method the interaction of compounds. The decomalso
is
;
,
posing agent
either water, an acid, or an alkali.
is
Marsh-gas, CH 4 ethylene, C 2 H 4 acetyC 2 H 9 ammonia, NH 3 and phosphoretted hydrogen, may be produced by the action of water on some
(i) Water: lene,
PH 3
,
,
,
,
,
compounds of carbon, nitrogen, and phosphorus. Aluminium carbide, A1 4 C 3 yellow transparent crystals produced ,
by heating a mixture of carbon and oxide of aluminium to whiteness in the electric furnace, on treatment with water yields
puremethane,Al 4 C 3
+ 2H,O = 3CH 4 + 4 A1(OH) 3 1
.
carbide, black crystals produced by heating in electric furnace a mixture of manganese oxide and
Manganese the
a mixture of equal volumes of hydrogen and methane, Mn 3 C + 6H 2 O = 3Mn(OH) 2 + 4 + Lithium, calcium, strontium, and barium carbides also formed in a similar manner in the electric furnace yield
carbon, yields
acetylene with water,
Li 2 C 2 + 2H.,O J
CaC 2 + 2H 2 O = Ca(OH)2+ C 2 H,." cerium, CeC 9 lanthanum, LaC ,
.
= 2LiOH + C 9 H 2
L>
The
carbides
;
of
and yttrium, YC 9 mixture of methane, ethylene, and acetylene, sometimes mixed with hydrogen ,
thorium,
C9H4
H
CH
ThC 2
,
,
yield
,
a
;
INTERACTION OF COMPOUNDS
37
U
C 9 , gives methane, ethylene, and and uranium carbide, hydrogen, but no acetylene. Magnesium or calcium nitrides, prepared by heating magnesium or calcium in a current of nitrogen, = 2NH 3 + yield ammonia with water: Mg 3 N 2 + 6H.,O metallic
3Mg(OH).
7,
and calcium phosphide, produced by heat-
ing lime with phosphorus, on treatment with water simiCa 3 P 9 larly gives off phosphoretted hydrogen: 2
+ 6H O =
3Ca(OH) 2 + 2PH 3
.
The
sulphides of magnesium and are also decomposed by water,
aluminium, MgS and A1 S 3 , with production of hydrogen sulphide and the hydroxide = Mg(OH), + ELS ; A1.,S 8 of the metal : MgS + 2
H.OH
+
6H.OH - 2A1(OH) ? + 3 H 2 S.
The
halides of a certain
number of elements are
at
once
decomposed by water with formation of a hydride of the Boron, silicon, halogen and a hydroxide of the element. titanium, phosphorus, sulphur, selenium, and tellurium The chlorides, bromides, and iodides are thus resolved. method is practically made use of in preparing hydrogen bromide, HBr, and iodide, HI, by help of phosphorus. But the previous preparation of phosphorus bromide or iodide is unnecessary. It is sufficient to add bromine to water in contact with red phosphorus, and hydrogen bromide is evolved ; or to warm a mixture of iodine, water, and red phosphorus.
The
use of yellow phosphorus
is
not
advisable, for the action is apt to take place too violently if it be used. It may be supposed that the phosphorus and halogen unite to form the pentahalide, which is then immediately
4 H,0
decomposed by the water, thus: PBr (or PI 5 ) r
= H 3 PO 4 + 5 HBr(or 5 HI).
The
+
gaseous hydride
be collected over mercury or by downward displacement, or it may be dissolved in water and a solution of
may
hydrobromic or hydriodic acid prepared. commercial method of producing hydrogen chloride, HC1, depending on the decomposition of magnesium chloride when heated in a current of steam, has been patented ; it results in the formation of a compound of
A
MODERN CHEMISTRY
38
oxide and chloride of magnesium, while the hydrogen of the water unites with a part of the chlorine ; the resulting gaseous hydrogen chloride is passed up towers, and comes into contact with water, thus yielding a solution chloric acid.
(2) In is
formed
many is
cases the
compound from which the hydride
not decomposed by water
hydrochloric acid, must be present. not easily explained
and
OH
it
;
of hydro-
may be
;
an acid, generally reason of this is
The
+
that the very
few ions of
present in water are sufficient to effect the
H
decom-
position in some cases and not in others, and that when an acid is necessary the much larger number of ions of hydrogen present in its solution is required ; also it is
known
that
the
heat
evolved
during the decomposition
compounds which are altered by water is greater than that which would be evolved by those which resist its action were they to be attacked by water.
of
those
Many -hydrides are prepared by the help of acids. Magnesium boride, Mg 3 B.2 , yields with hydrochloric acid a trace of BH 3 but as this compound is a very unstable gas, almost all of it decomposes into boron and hydrogen. The similar compound, Mg 9 Si, produced by heating a mixture of silica and magnesium powder to redness, when mixed with hydrochloric acid yields hydride of silicon, SiH 4 , as a colourless, spontaneously inflammable gas: Mg.,Si + ;
4HC1. Aq = 2MgCl 2 Aq + 8iH 4
Arseniuretted hydrogen, and antimoniuretted hydrogen, SbH 3 , are prepared from sodium or zinc arsenide or antimonide : Na3 As +
AsH 3
.
,
HCl.Aq = 3 NaCl.Aq + AsH 3 Zn 3 Sb 2 + 6HCl.Aq = These gases, however, may be ob3ZnCl 2 .Aq + 2SbH 3
3
;
.
tained
mixed with hydrogen
if a solution
of oxide of arsenic
or antimony in hydrochloric acid, which yields chloride of The first change arsenic or antimony, is treated with zinc. is
the replacement of the zinc by the arsenic or antimony,
thus
:
2AsCl 3
.
Aq + 3 Zn = 3ZnCl 2 Aq + 2 As.
Electrically
HYDRIDES
39
neutral zinc replaces positively charged arsenic, itself becoming positively charged. The arsenic and the unattacked
zinc form a couple, and the hydrochloric acid
+ ++ ++ 2HCl.Aq + Zn = ZnCl 2 .Aq + 2H +
-
is
electrolysed,
the hydrogen ion unites with the arsenic, negatively charged in the electric couple, forming electrically neutral hydride of arsenic, which escapes
+
as gas, 3
;
---
H + As = AsH
of combination
at the
3
.
An element in this form,
moment of liberation,
is
capable
said to be in the
word derived from " nascere," to be born. from an ordinary element in being on the point of losing an electric charge, and it may either be evolved in
nascent state, a It differs
+
+
H H H
the free state by combining with itself, as + = 2, on giving up its charge, or it may en.ter into some other form of combination, as in the case explained. This process of preparing arsenic or antimony hydride is used as a test for the elements
Marsh, and
or
arsensic
It
antimony.
was devised by
the hydrides are very easily decomposed by a high temperature, the gas, if caused to pass through a red-hot tube, is decomposed, giving a deposit of arsenic as
The former is more easily (grey) or antimony (black). oxidised than the latter, and dissolves in a solution of bleaching-powder, process
is
in
which the
particularly
latter is
applicable
where
This
insoluble.
poisoning with
arsenic or antimony is suspected. Te. 2 S, ELSe, Hydrogen sulphide, selenide, and 2 telluride are prepared by treating a sulphide, selenide, or
H
H
telluride
with dilute sulphuric or hydrochloric acid
:
FeS
SO 4 .Aq = FeSO 4 .Aq + H 2 S Sb2 S 3 + 6HCl.Aq = 2SbCl 3 .Aq + 3 H 2 S. Na 2 Se.Aq + H 2 SO 4 .Aq = -f
H
2
;
.
Na 2~SO 4 .Aq + H 2 Se. Acids. Hydride of fluorine, chlorine, bromine, and when dissolved in water, are termed *' acids." As already mentioned, this name was originally applied to comiodine,
MODERN CHEMISTRY
40
pounds which possess a sharp taste and change the colour of certain vegetable colouring matters. The word was later extended to apply to compounds similar in function, taste, which attack the carbonates, causing them to effervesce, and which yield salts with the oxides of metals. All acids contain hydrogen, and it is
although not acid to
An
now possible to define them in a very simple manner. acid, in fact, is a compound which yields hydrogen ions when dissolved in water, or in some other solvent capable This definition applies to the of causing ionisation. hydrides of fluorine, chlorine, bromine, and iodine ; and also to those of sulphur, selenium, and tellurium ; for on
+-
solution they ionise thus
+
HF.Aq
:
-
+-
HCl.Aq
;
HBr.Aq;
;
But
HI.Aq; H.SH.Aq; H.SeH.Aq; H.TeH.Aq.
not confined to them, for the hydrogen may be united, not with a simple element, but with a complex group of it is
- -
+
elements, as in
H
solution, a solution
therefore a
or
in
Now,
HNOg.Aq.
of sulphuric acid
of hydrochloric acid, it is
+
SO 4 .Aq
2
is
less ionised
in dilute
than one
about the proportion of 1:2, and so that if a hydroxide, such ;
weaker acid
as sodium hydroxide, be presented to a mixture of equal numbers of these molecules, in quantity requisite for only one of them, chloride of sodium will be formed in greater than sodium sulphate ; on heating a quantity yet,
halide is
with
a volatile
sulphuric
compound,
acid, it
because
removes
hydrogen chloride from the sphere while the sodium
itself
of action in a non-ionised state remains as sulphate. Hence these hydrides prepared.
Hydrogen
distilling calcium as " fluor-spar,"
fluoride,
fluoride, a
HF 2
2,
is
compound
with sulphuric acid
platinum: CaF 2 + lead or platinum
H SO 2
4
may be
thus
generally prepared by naturally occurring of lead or
in vessels
- BaSO 4 + H 2 F 2
.
The
use of
obligatory on account of the action of hydrogen fluoride on glass or porcelain, the materials of which flasks and retorts are usually made ; for is
HALIDES
41
silica which they contain, hydrogen fluoride attacks the = SiF 4 + forming with it silicon fluoride: SiO.2 + 2H 2 F 2 2H 9 O. Gold is almost the only other metal which resists There is no such diffithe action of hydrogen fluoride.
culty with the other halides.
prepared
by
common
salt
and
oil
Hydrogen
from
distilling
of
a
vitriol
:
glass
chloride,
retort
HC1,
is
mixture of
a
NaCl + H.2 SO 4 =
HNaSO 4
On
+ HC1.
a large scale this preparation is carried out in rotating circular furnaces, the mixture of salt and vitriol being delivered in through a hopper above, and at the high
temperature the action goes further, and di-scdium sulphate is
produced:
2NaCl + H 2 SO 4 = Na2 SO 4 + 2HCL
The
passed up towers filled with coke, and exposed to a descending stream of water, in which it dissolves, forming is
gas
a saturated solution of hydrochloric acid, or, as
it
used to
be called, "muriatic acid" (from "muria," brine). Hydrogen bromide, HBr, and iodide, HI, may similarly be produced by distilling together bromide or iodide of sodium or potassium with exactly the right weight of sulphuric acid for the equation
2KBr
(or
aHBr
zKI) + H 2 SO 4 .Aq =
K SO 4 .Aq + 2
But
in these cases, the hydrogen bromide (or 2HI). or iodide is very apt to exert a reducing action on the sul-
phuric acid, depriving
H SO 2
4
it
of an atom of oxygen, thus
+ 2HI = H 2 SO 3 + H 2 O + I 2
.
Hence
it
is
:
advis-
H HK PO
PO 4 , a compound not thus g 2KI = reduced zHI. 3 4 + 4 + 2 All these halides come over as gases, and may either be collected over mercury or by " downward displacement," i.e. by delivering them to the bottom of a jar containing air, which owing to its less density is forced upwards, and escapes at the mouth of the jar. They cannot be collected over water, for they are readily soluble in it. The compound termed hydrazoic acid (from the 3, French term for nitrogen, "azote"), is also liberated in able to use phosphoric acid, :
H PO
HN
the gaseous form by acid.
(3)
warming its sodium salt with sulphuric readily soluble in water. Certain hydrides are set free by the action of an
It, too, is
MODERN CHEMISTRY
42 alkali, i.e. the
hydroxide of one of the metals of the sodium
It is true that the change may be or the calcium group. produced by other hydroxides, but they are not so efficient, and not so generally employed. Among these are ammonia,
NH
NH
3,
acids
;
These bodies unite with and hydrazine, 2 4 for example, ammonia and hydrogen chloride form .
NH
NH
when mixed: HC1 4 C1, 3 + This compound is produced by a change in valency of the nitrogen atom in ammonia it is a triad, N"', but on union with hydrogen chloride the valency of the v On distillation of a mixture of nitrogen becomes five, N
ammonium
= NH 4 C1.
chloride,
;
.
ammonium
chloride with caustic soda or with slaked lime, either in presence or absence of water, the following change .occurs
NH
:
4
C1 +
Na O H = NaCl +
NH
3
2NH 4 Cl + Ca(OH) = CaCl + 2NH + 2H 2
2
3
2
+
H
O.
2
O
;
TThe
ammonium hydroxide, unstable when heated, being 4 Hydrazine, a comdecomposes into ammonia and water. is similarly liberated from its 4, pound of the formula 2 initial
change
NH OH
;
is
this
the formation of
substance,
NH
chloride.
The
On
usual
source of commercial
ammonia
is
coal-gas.
of which contain nitrogen, it may be imagined that when methane, the principal constituent of coal-gas, is strongly heated it splits into carbon and This hydrogen, at the moment of its formation, hydrogen. is in the nascent state, and it unites with the nitrogen, which distillation
of coal,
all varieties
As ammonia is very easily also in the nascent condition. soluble in water, while the other constituents of coal-gas are
is
is deprived of ammonia by passing sparingly soluble, the gas " it scrubbers," pipes containing broken bricks kept through The ammonia dissolves, while the coalmoist with water.
The solution is next mixed with hydrogas passes on. The residue of chloric acid and evaporated to dryness. ammonium chloride is then distilled with lime, as previously described.
The ammonia
is
received in water, and brought
form of a concentrated " is given. which the name "liquor ammonias into the
market
in the
solution, to
PROPERTIES OF HYDRIDES
43
() Certain double hydrides are formed by the addition Ammonia and hydrazine unite of one hydride to another. with hydrides of the halogens to form salts, such as ammoC1 ; but as these bodies show analogy nium chloride, 4
NH
with
salts
of the metals, they will be reserved until the
latter
are considered.
General Nature of the Hydrides.
Hydrides of
lithium, sodium, potassium, iron, nickel, palladium, and platinum differ from the others in character ; they are solid bodies,
decomposed by
heat.
Graham,
indeed,
who
investigated that of palladium, was struck with the metallic nature of the substance, and was inclined to believe that it might be regarded as an alloy of a metallic form of hydrogen,
"
and it was for which he gave the name " hydrogenium long believed that liquid hydrogen would show the characteristic property of metals, metallic lustre. But this anticipation to
;
has not been fulfilled.
and
Liquid hydrogen
is
a colourless body
;
described as having a white crystalline But it must be confessed that appearance, like ice froth. hydrogen shows a marked similarity to metals in many of its solid
hydrogen
is
be frequently seen in the sequel. hydrides may be divided into three Those which react with neither acid nor bases, classes and which may therefore be described as neutral. To this class belong the hydrides of boron, carbon, silicon, That of phosphorus nearly falls arsenic, and antimony. into the same category, for its compounds with acids are The next class those which react with very unstable. bases comprises water and the hydrides of sulphur, The compounds are termed selenium, and tellurium. hydroxides, or, in the case of sulphur, hydrosulphides. These will be considered later, but an instance may be given here When lime is moistened with water it is slaked, with formation of calcium hydroxide, thus CaO + 2 = Ca(OH) 2 The hydrides of fluorine, chlorine, bromine, and iodine also belong to this class ; but in their case an
compounds,
The
as will
remaining
:
:
:
HO
.
exchange takes
place, thus:
CuO + 2HCl.Aq = CuCl 2 .Aq
MODERN CHEMISTRY
44
H
= O. Hydrazoic acid is capable of similar reactions. Such hydrides, with the exception of water, are generally The last group of hydrides, ammonia and termed acids. hydrazine, and, in one or two isolated cases, hydrogen phos-
NH
+ HC1 = phide, unite with acids, forming salts, thus 3 I. C1 It appears that the pre3 + 4 4 sence of water is necessary for at least the first of these combinations ; for if perfectly dry hydrogen chloride is mixed with perfectly dry ammonia, no combination results. It is perhaps allowable to suppose that the presence of moisture leads to ionisation of the hydrogen chloride, and that the ionised molecule is capable of entering into combination, while the non-ionised molecule is without action These compounds will be treated of on the ammonia. under the heading of " salts/' The hydrides of boron, carbon, silicon, phosphorus, those of arsenic, and antimony are insoluble in water :
NH
;
PH
HI-PH
;
nitrogen, sulphur, selenium, tellurium, and the halogens are soluble. With the exception of certain hydrides of carbon, to be afterwards described, and water, all the
The
fact that rest are gases at atmospheric temperature. water is a liquid, and not, as might be expected, a gas, recomment. It is noteworthy that water-gas possesses
quires
the density 9, corresponding to the molecular weight 1 8 ; hence there can be no doubt that in the gaseous state water O. But it is known that compounds of has the formula 2
H
sulphur,
which are
in
formulas,
and
in
many
properties
analogous to compounds of oxygen, possess higher boilingFor points than the corresponding oxygen compounds. instance, bisulphide of carbon, CS 2 , boils at 44, whereas But water boils at carbon dioxide boils at about -80.
100,
and, contrary to expectation,
its
analogue, sulphuretted
hydrogen, condenses to a liquid at a temperature much below o. Now, it has been found by a method depending on the rise of liquids in capillary tubes, that while the molecular weight of most substances in the state of liquid is identical with those which they possess in the gaseous state,
HYDROCARBONS
45
molecular weight of water is considerably too great. conclusion follows, therefore, that the molecular weight of water should be expressed by a more complex the
The
formula than
HO
H
O 9 or by one even possibly by 4 Gaseous hydrogen fluoride, unlike its higher molecular weight than that ex-
more complex. congeners, has a
;
HF
pressed by the formula F 2. leads to the formula 2
H
;
,
determination of
These
its
density
probably to be possess a higher
facts are
explained by the view that oxygen may valency than 2, and fluorine than I, at relatively low temIt is not unlikely that the structural formula of peratures.
H
liquid
fluoride
/H
and that yO=OS \H H/ HF=FH, where oxygen acts as
water
is
,
of hydrogen a
tetrad
and
fluorine as a triad.
The hydrides of carbon, or Hydrocarbons. "hydrocarbons," are very numerous, and form an imIn many respects they are portant group of substances. analogous to the metals, and they yield derivatives comThe preparation of some parable with those of the metals. but in order to give a of them has already been described more complete idea of their structure and functions, a short description of other methods of forming them is annexed. Methane or marsh-gas, if mixed with its own volume of not sunlight, else the chlorine, and exposed to daylight ;
mixture would explode
CU^CHgCl + HCl. methane,
is
undergoes the
reaction
CH
4
-f-
The
soluble in
resulting gas, termed chloroether, a volatile liquid compound
of carbon, hydrogen, and oxygen. If pieces of metallic sodium are added to the solution, the sodium withdraws chlorine from the
On
CH in
analysis,
chloromethane and a gas is evolved. gives numbers answering to the formula if that were its formula, its molecular weight it
But g grammes would occupy 22.4 .
litres;
but 15
grammes
occupy only 11.2 litres; hence its molecular weight must be 30, and not i 5, and its formula cannot be but must 3
CH
,
MODERN CHEMISTRY
46 be
C2H
It
.
is
fi
the reaction
is
reasonable to suppose that the mechanism of
this
and that the two
H\ H C H/
:
CH
3
;
:C1
:
+ Na Na + Cl
C
/H H \H
;
groups on liberation join together,
forming the complex group,
H
H\ ;C H/
H
C
/H H. \H
Similarly,
mixing C 2 g , which is named ethane, with its own volume of chlorine, a reaction takes place like that with methane, and chlorethane is formed, thus C 2 6 + C1 2 = C 9 5 C1 + HC1. Chlorethane dissolved in ether and treated with sodium yields not C 2 5 but C 4 10 , and it may be
H
:
H
H
H
supposed that the constitution of the
H H H H
butane,
is
HC C C
CH.
H H H H
A
new hydrocarbon, mixture of chloro-
methane and chlorethane gives with sodium an intermediate
H H H
hydrocarbon, chlorine and
CJ3 8
,
propane,
HC C
CH.
H H H
When
propane are mixed in equal volumes, two result; they have identical formulas and
chloropropanes
molecular weights, and
it
is
believed that the difference
between them consists in the position of the entering atom of chlorine. In one case the chlorine replaces hydrogen attached to one of the terminal atoms of carbon, thus :
H H H the C C CH, while H H H H Cl H HC C CH. replaced H H H Cl
in
:
yield
Two
in
their
turn
other the medial hydrogen
These
is
two chloropropanes
two methylpropanes
or
butanes.
such substances are said to be isomeric, or to exhibit The following list gives the isomerism with each other. names and formulae of some of this series of hydrocarbons ;
HYDROCARBONS
47
where the difference between their formulae form
are said to
a
"
homologous
they
H H H H
Ethane.
H H H H HC C C CH H H H H
H H H C CH H H H
HC
Butane.
Propane.
H H H
H H H H H H H H H H
HC C CH
HCH H
2,
HC CH
Methane.
|
CH
series."
H HCH H
H
is
H
HC C C C CH Pentane.
Isobutane.
H HCH |
HC
CH
C
I
HCH H
H H
H H
H HCH |
H H
HC C CH
H H
I
HCH H
Tetramethyl-methane.
Isopentane.
Chloromethane, if mixed with its own volume of chlorine and exposed to light, yields a dichloromethane, thus : C1 + C1 2 = CL + HC1. This compound, which, 8 ? like chloromethane, is also a gas soluble in ether, on treating its solution with sodium, loses chlorine and is converted = 4 NaCl into ethylene, thus: C1 + 4 Na + CI 9
CH
CH
+
C=C
CH
CH
H H
.
The
H H
a tetrad, but the
carbon atom,
two atoms
it
will be observed,
are connected by a
is
still
" double
MODERN CHEMISTRY
48
bond/'
Homologues of ethylene
following are a few
are
known, of which the
:
H H C=C H H
HC C^C
Ethylene.
Propylene.
H H H
H
H
HHHH HHHH C=C HC C=C CH
HHHH
HC
C
H
H
H
HC
H
CH
C ||
HCH
H
Butylenes.
These hydrocarbons are characterised by the facility with which they combine with the halogens, forming oils they " or "oil-makers." therefore, been termed ;
have,
olefines,"
They into
also unite
paraffins,
The
termed.
as
equations which follow illustrate this
HC 2
H
11+ 2
with nascent hydrogen, and are converted the members of the former group are
C
H
Cl
= I
Cl
H
CC1 2 "I 2
CC1
CH
~
[]
CH
2
CH + 2H=
:
3
|
CH
3
the further action of chlorine on dichloromethane, trichlorometliane, or chloroform, CHC1 3 , is produced.
By
Chlorine can also be withdrawn from chloroform by sodium, C 2 2 , is formed: HCCl 3 + 6Na + Cl 3 = 6NaCl + Here the two carbon atoms are represented as united by a treble bond, and each carbon atom is still believed to remain tetrad. Acetylene is also characterised by the ease with which it unites with
and acetylene,
H
CH
HC=CH.
chlorine, forming a tetrachlorethane . C1 Here, also, other 3 2
are
HC-CHC1
HC=CH
+ 2C1 2 = members of the series :
known.
The
passage of acetylene "through a red-hot tube is that is, two or more moleattended by " polymerisation ; In this case, three cules unite to form a more complex one.
HYDROCARBONS
49
molecules of acetylene combine to form a molecule of the formula C 6 Hg, a compound to which the name benzene is It is produced in large quantity by the distillation applied.
of coal, and is separated from coal-tar oil by distillation. Its carbon atoms are imagined to form a ring, because, among other reasons, it yields only one mono-chloro-sub-
H H H C C=C
stitution
product
: ||
C=C
C
gives
on
treatment
with
H H H H H Cl c_ c=c chlorine,
CL,
||
;
c_ c=c H H H |
and as
all
the hydrogen atoms
in the molecule are symmetrically arranged with respect to the carbon atoms, this condition is fulfilled. The four first members of the methane series are gases ; those containing a greater number of atoms of carbon up
and the higher members are solids. which is burned in paraffin lamps consists of a mixture of the liquid members, and paraffin candles largely consist of the solid members. They are all practically
to eleven are liquids,
The
oil
insoluble in water. perties,
The
and benzene
is
olefines
have similar physical pro-
a volatile liquid.
Iodine, sulphur,
and phosphorus dissolve in the liquid hydrocarbons. These and other hydrocarbons may be considered
as
somewhat analogous to the metals the analogy appears in the methods of formation and formulas of their derivatives. ;
VOL.
II.
CHAPTER
III
The Halides of the Elements Double Halides Endothermic Combinations Hydrolysis Oxidation and Reduction
Mass*Action.
The Halides. Compounds of fluorine, chlorine, bromine, and iodine are thus named. They fall into classes when the elements are arranged according to the periodic system.
we have
Taking the chlorides as typical of the the following table
halides,
:
HC1 BeCl 2 BC1 3 CC1 4 NaCl MgClo A1C1 3 SiCl 4 LiCl
KC1 CaCl 2 ScCl3 TiCl 4 RbCl SrCl 2
YC13
ZrCl 4
CsCl BaCl 2" LaCl 3 CeCl 4 YbCl,
...
NC1 3
PC1 5
PC1 3
SF6
AsCl 3 ... SbCl 5 SbCl 3 ErCl 3 ... ...
ThQ 4
SC1 4
OC1 2
...
FC1?
SC1 2
...
C1C1
...
SeCl 4
...
TeCl 4 TeCl 2
IC1 3
BiCl 3
CrCl 2 MnCl 3 CuCl ZnClo GaCL GeCl 4 VC1 5 VC1 3 AgCl CdCf2 InCl 3 SnCl 4 NbCl 5 NbCl 3 ... MoCl 4 MoClo NdCl 2 TbCl 4 PrCl 3 ... ... ... GdCl, WC1 6 WC1 4 WC1 2 ... ... HgClo TIC1 3 PbCl 4 TaCl 5
FeCl 3
OsCl 4
FeClo
...
RuCl 3 RuClo
...
OsCl 3
OsCl 2
IrCl 4
CoCl 3 CoCl 2 PdCl 4 RuCl 3 ... IrCl 3 50
...
PtCl4
...
NiCl 2 PdCl 2
...
PtCl 2
...
THE HALIDES
51
Besides these compounds, which present considerable exist which have Jess claim to order. regularity, others Thus, KI 3 is also known it is unstable, but CsI 3 is reAgain, CuCl 2 and AuCl 3 exist, also latively stable. HgCl. In the next group, GaCl 9 InCl, and InCl 2 are also ;
,
T1C1.
The
following group contains Besides and PbCl 2 PbCl 4 is very unstable. VCl.'and VC1 3 VC1 4 and VC1 9 are also known ; and in the next group, CrCl 8 MoCl 3 and MoCl 5 , also WC1 5 , These compounds are difficult to UClg, and UC1 5
known,
as well
as
SnCl.,
;
,
,
,"
.
classify.
The bromides and iodides, as well as the fluorides, corresponding to many of these chlorides in formula, are also known. Where they are of special interest, they will be alluded to in the sequel.
The
characteristic of the halides of the elements of group is that they are all soluble white salts, In dilute solution they are all ioncrystallising in cubes. ised, and even in strong solution a large percentage of ions Hence they all react as metal ions and as haloare present. Thus, for instance, with silver nitrate, which is gen ions. the usual test for ionic chlorine, the following reaction takes the lithium
NaCl.Aq +
:
place
AgNO 3 .Aq = NaNO
3
.Aq + AgCl.
Practically insoluble, and therefore practically non-ionised, silver chloride is precipitated, and free ions of sodium and
the
nitrate
solutions are
group remain in solution. mixed, that portion which
If concentrated is
ionised reacts
;
removed from solution, the originally nonionised molecules of sodium chloride are ionised, because the solution becomes more dilute as regards sodium chloride,
and
as
it
is
and they, too, enter into reaction.
In a similar way, the metal ions react in presence of a suitable reagent. Another point to be noticed is that these salts are not hydrolysed, that is, do not react with water to give hydroxide and acid to any appreciable extent, and the usual method alkali
of preparing them depends on these
facts.
They may
MODERN CHEMISTRY
52
be obtained by the addition of halogen acids to the hydroxides or carbonates of the metals dissolved in water,
all
thus:
KOH.Aq + HBr.Aq=KBr.Aq + H 2 O.
be noticed that the water
is
not ionised, nor does
will
It it
hydro-
potassium bromide ; hence, on evaporation, as concentration increases, the number of ions of potassium and bromine becomes fewer and fewer, and after the
lyse the
water has been removed the pure dry carbonate the action is similar.
salt
Li 2 CO 3 .Aq
HO
+ zHI.Aq = 2LiL Aq +
dilute solution the acid
H CO 2
3
is
The
a
would be
2
With
left.
equation
+ CO 2
liberated
;
.
is
In it is
a
very weak acid, i.e. it is comparatively very slightly ionised into
+
aH.Aq
and
poses into
CO 3 .Aq and, moreover, and CO 2 hence ;
HO 9
;
it
is
it readily decomremoved from the
sphere of action as it is formed, and on evaporation the salt is left behind, as in the previous example. Sodium and potassium chlorides occur in nature ; th< sea, which contains from 3.8 to 3.9 per cent. Deposits, which have undoubtedly been formed by the drying up of inland seas, are found in many places. At Stassfurth in S. Germany there are large deposits of all the salts present in sea-water, including common salt, chlorides and sulphates of magnesium, potassium, and sodium, and calcium sulphate ;
former in the
these have been deposited in layers in the order of their solubilities, the less soluble salts being deposited first. Bromides and iodides are also present in minute quantity in
the residues from the evaporation of sea-water. Solutions of the halides of the beryllium group of elements can also be made by acting on the hydroxides or carbonates
To take barium chlo++BaCO g .Aq+ 2HCl.Aq= BaCl 2 .Aq
of the metals with the halogen acid.
+ +-
ride
as
an example,
+ H 2 O + CO 2
Now
+
barium carbonate is nearly insoluble in water, but the portion which dissolves is ionised ; and, as explained above, when the portion which is ionised has .
THE HALIDES
53
reacted, its place is taken by more of the carbonate entering into solution ; so that finally all is changed into chloride.
With
the hydroxides, the same kind of reaction takes place
:
= CkBr^Aq + 2H 2 O. Ca(O~H) 2 .Aq + 2 HBr.Aq These salts are also white and soluble in water. There is, however, one exception, namely, calcium fluoride, CaF , It forms which occurs native as fluor- or Derbyshire spar. colourless cubical crystals, and is the chief compound of fluorine. +-
It
++ produced by precipitation: CaCl
is
-
+
2KF.Aq = CaF 2 + 2KCl.Aq.
non-ionised, and comes
down
The
.Aq +
calcium fluoride
is
an insoluble form. Water of Crystallisation. The other halides of this group crystallise with water of crystallisation ; its amount varies from 7 molecules, as in BaI 9 .yH 9 O, to I as in ZnCl .H 9 O. The retention of this so-called " water of " has not crystallisation yet been satisfactorily explained. It was for long believed that such compounds were " molecular," as opposed to atomic ; that is, that the water molecules combined as wholes with the salt, and not by virtue of their atoms ; but it is more probably to be explained by the tetravalency of oxygen, although even with this in
i7
not easy to ascribe satisfactory constitutional It must at the same time be assumed
assumption
it is
formulae in
all cases.
atoms are of a higher valency than unity possibly triad, or even pentad. These salts are hydrolysed in solution to a small extent
that the halogen
;
;
thus a solution of magnesium chloride, besides containing a large number of ions, has also reacted with the water to form
hydroxide and hydrogen chloride:
= Mg(OH) 9 + 2HC1.
As
centrated on
the
evaporation,
MgCl 2 + 2H(OH)
the solution becomes con-
hydrogen chloride
volati-
with a part of the water ; and a mixture, or rather a compound, of the oxide and chloride remains. Hence these chlorides cannot be obtained in a pure state by evaporating their solutions. They exhibit another property, however, lises
MODERN CHEMISTRY
54
possible to obtain them in a pure state, " namely, the power of forming double halides." This prois not well marked with the halides of calcium, barium, perty and strontium, but the halides of beryllium, magnesium,
which makes
it
We
zinc, and cadmium are notable in this respect. have, for example, .KC1.6H 2 O, ZnCl 2 and many 2 4 Cl, In solution, such compounds are mainly similar bodies.
.NH
MgCl
ionised into their simple ions, but on evaporation the nonionised salt separates in crystals, and is not subject to Hence such salts can be dried without decomhydrolysis.
The ammonium salts, when sufficiently heated, position. lose ammonia and hydrogen chloride by volatilisation, and the
NH salts
anhydrous halide 3
+ HC1. is
is
The mode
possibly
owing
MgCl 2 .NH 4 Cl = MgCl 2 + of combination of these double
left]:
to the fact that
the halogens are
.C1-C1K capable of acting as triads
;
thus
Zn
may
be
\C1 taken as the constitutional formula of that particular salt. The mono-halides of copper, silver, and gold may be attached to the first group ; and if that is done, the monohalides of mercury must also be included. These comall insoluble in water, and are consequently obtained by precipitation or by heating the higher halides, where these exist. Thus CuCl and AuCl are obtained
pounds are
by cautiously heating CuCl 2 and AuCl g they are white insoluble powders. Cuprous chloride is more easily obtained by removing half the chlorine from cupric chloride dissolved in concentrated hydrochloric acid, by digesting ;
it
with
metallic
copper:
CuCl 2 .2HCl.Aq + aHCl.Aq a brown compound, which is
+ Cu = Cu 9 Cl 2 .4HCl.Aq,
decomposed by water into Cu 2 Cl 2 and 4HCl.Aq ; the cuprous chloride is thrown down as a snow-white powder. With silver and mercury, the chlorides AgCl and HgCl are formed by precipitation from the respective nitrates, AgNO 3 and on addition of soluble chlorides. The bromides 3, and iodides are similarly formed, and are also insoluble.
HgNO
THE HALIDES
55
There
are several interesting points connected with these halides. First, as regards their colour; the chlorides are white; cuprous bromide is greenish brown, while the brom-
and mercury are yellow ; and cuprous brownish, and the iodides of the other metals darker It appears as if the colour was yellow than the bromides. influenced both by the metal and by the halogen. Next, the chlorides of copper and mercury give evidence of possessing the double formulas Cu 2 Cl 2 and Hg 2 Cl 2 , which would imply that the metals were only pseudo-monads, and that the structural formulas should be Cl Cu Cu Cl and Cl Hg Hg Cl ; and this would correspond with ides
of
iodide
silver, gold,
is
chlorides CuCl 2 and HgCl 2 are also on the other hand, as AgCl in the state of gas has the simple formula given to it, it may be that it is the halogen which forms the bond of union between the two Silver forms no higher half-molecules, thus CuCl=ClCu. the fact that the
known
;
but,
:
halides.
The
fluorides of these elements differ
from the others
in
being soluble in water ; they are prepared from the oxides with hydrofluoric acid. They are very difficult to dry, for they undergo the reverse reaction, and are hydrolysed into
oxide and hydrogen fluoride on evaporation.
Copper and mercury
also function as
dyads;
that
is,
their ions are capable of carrying a double electric charge under certain circumstances. What the mechanism of this
change is, we do not know but the change in valency can be induced by presenting to the element a larger amount of halogen, if it is desired to increase the valency, or by remov;
The addition ing halogen if the opposite change is required. of halogen to the mono-halide is in each case an exothermic change, and its converse is an endothermic one. Cuprous or mercurous chloride, heated in a current of chlorine
changes to cupric or mercuric chloride, and the converse change can be brought about by heating the higher halide in a current of hydrogen, or by exposing the lower halide to the action of nascent hydrogen ; but it is difficult to
MODERN CHEMISTRY
56
prevent the action in the latter case from going too far and solution of cupric chloride saturated yielding the metal.
A
with sulphurous acid in presence of hydrochloric acid, and then diluted with water, gives a precipitate of cuprous chloride
:
2CuCI 2
.
Aq + H 2 SO 3 Aq + 2HCl.Aq + H O = .
Cu 2 Cl 2 4 HCl.Aq + H 2 SO 4 Aq. .
The
.
sulphurous acid re-
moves oxygen from water, liberating hydrogen in presence of the cupric chloride, and the latter is deprived of half its chlorine and reduced to Similarly, cuprous chloride. stannous chloride
The
chloride :
forms a reducing
2HgCl 2 Aq + SnCl 2 .
.
agent for mercuric Cl 2 + SnCl 4 Aq. 2
Aq = Hg
.
converse change can be produced by exposing the lower halide in presence of halogen acid to the action of nascent = 2CuCl 2 + H,O. oxygen : Cu 2 Cl 2 + 2HCl.Aq +
O
This oxygen
of copper
.
Aq
O
be molecular, 2, but for the formation of the higher halide of mercury, it must be derived from some substance capable of parting readily with oxygen, such as nitric acid. in the case
Cupric iodide is very unstable, iodine, forming cuprous iodide.
On
may
and readily yields up mixing cupric chloride
with potassium iodide, the cuprous iodide
is
precipitated
q+I 2
.
It
is
:
to
be noticed that the dyad cupric ions have lost two charges, and that these have neutralised the two negative charges of the iodine ions, causing them to be precipitated. (Inasmuch as the cuprous iodide is insoluble, it should not have had the ionic signs attached
show the changed
;
but they have been kept in order to Mercuric iodide is an insoluble )
valency.
scarlet precipitate, and is therefore best produced by preIt dissolves, however, in a solution of potassium cipitation.
iodide, forming a double salt, of which more shortly. Auric chloride contains triad gold, and thus has the It is not produced by the direct action formula AuCJ 3 of chlorine on gold, because the temperature of attack is above the temperature at which the compound is decomposed. .
But
it is
in a current of chlorine, possible to volatilise gold
THE HALIDES
57
few molecules escape decomposition and are along the tube through which the chlorine is d, and on cooling the gold is deposited, owing to the It decomposition of the chloride at a lower temperature. may appear paradoxical that the chloride is stable at a because
a
volatilised
higher temperature than that at which it decomposes ; but it is to be presumed that the difference of temperature
between one favourable to an exothermic and to an endois very small ; and as endothermic substances increase in stability on rise of temperature, the chloride is capable of volatilisation ; on cooling it becomes unstable and The undergoes decomposition with deposition of gold. usual method of preparing this salt is to dissolve gold in a mixture of nitric and hydrochloric acids. This mixture yields ionic chlorine, the negative charge of which neutralises the positive charges of the gold ; but there are corresponding thermic action
negative charges set free,
N0
3
of the
nitric acid,
The
negative charges.
which are transferred
to the ion
it into 2O, with its four combines with the hydrogen,
converting latter
-
-
forming electrically neutral water:
Au = 2H,O + AuCl 3 .Aq + NO. Auric chloride forms dark red crystals it is soluble in when mixed with chlorides of the alkali metals ;
water, and
salts termed aurichlorides. The potassium example, has the formula K AuCl 4 ; it is soluble in water, but, unlike the "double salts," such as MgCl 4 .2KCl,
forms a set of salt, for
already alluded to,
it
is
ionised
ions like these, but into the ions
AuCl 4
.
At the same time there exists
number of simple at
by water, not into" simple + K and the complex group in the solution a small
on electrolysis gold is deposited the kathode, but the primary effect of the current is to ions, so that
The solution of merpotassium iodide, of which mention was half-way example of the same kind. Its solu-
send the aurichloric ions to the anode.
curic iodide
in
made before, is a
MODERN CHEMISTRY
58
+
tion contains ions of
K
and
HgI 3
,
but these are
mixed with
+
K
a much larger and I and proportion of the simple ions, ++ and I . All grades of such salts are known ; indeed it
Hg
is
probable that the double
salts,
such as magnesium-potassium
chloride, contain a small number of complex ions of MgCl 3 . These halides have been considered at length because Use will be made of the they form types of the others.
examples given in treating of the remaining halides. We have seen that the halides may undergo either ionisation or hydrolysis, or both at once. The ionisation may be more or less complete, and the hydrolysis is promoted by
and by a high temperature. The remaining halides display both these kinds of behaviour, and according as one or the other prevails, the methods of preparing them are dilution
In certain cases, moreover, the halides form usually those of the alkali less apt to be hydrolysed, and yield different complex ions. The halides of carbon and nitrogen belong to neither of these classes, for they are insoluble in and unacted on by water. As neither carbon nor nitrogen is acted on by the halogens (excepting that carbon burns in fluorine), they must be prepared indirectly by acting on one of their compounds with the halogen. Methane or carbon disulphide is chosen for the former, and ammonia in preparing the latter. By passing a current of chlorine saturated with the vapour of carbon disulphide through a red-hot tube, the chlorides of both carbon and On CS 2 + $C\ 2 = CC1 4 + S 2 C1 2 sulphur are formed treatment with water the sulphur chloride is decomposed, while the chloride of carbon may be distilled off ; it forms Its smell resembles a colourless liquid boiling at 76.7. that of the closely allied chloroform, CHC1 3 , and it is also For the preparation of possessed of anaesthetic properties. nitrogen chloride a jar of chlorine is inverted over a affected.
compounds with other halides, metals or hydrogen, which are
:
.
THE HALIDES saturated
59
of ammonia in water oily drops are bottom of the vessel 3 Aq + 3HCl.Aq; the HC1 unites with ammonia,
solution
formed which
;
settle to the
:
NH
.
3Cl 2 = NCl 3 + forming ammonium chloride.
Endothermic Combination.
This body
is
fearfully
explosive, for its formation is attended by great absorption of heat ; but during its formation the reagents do not grow
cold ; for the formation of ammonium chloride is a highly exothermic reaction, and the amount of heat evolved by its formation is greater than that of the equivalent amount of chloride of nitrogen ; hence the change as a whole is It is thus that endoaccompanied by evolution of heat. thermic compounds are usually formed by virtue of a :
The slightest simultaneous action in which heat is evolved. shock causes the decomposition of such endothermic bodies ; if
one single molecule
is
decomposed,
it
evolves heat and
brings about the decomposition of its neighbours ; and as all the molecules are in close proximity to each other, and as
the products, nitrogen and chlorine, are both gases, and are, moreover, much raised in temperature by being set free, the
decomposition
is
accompanied by sudden and enormous ex-
Nitrogen iodide, prepared by adding a solution pansion. of iodine to aqueous ammonia, is a black solid of the formula
NI 3 .NH 3
;
it is
also explosive.
The
fluorides of boron and silicon are both produced the action of a strong solution of hydrofluoric acid on the by oxides ; but it is necessary to have some agent present
withdraw water, such as concentrated sulphuric acid. These compounds are both gaseous. Their formation is shown by the equations: B 9 O 3 + 6HF = 2BF 3 + 3H O SiO + 4HF = SiF 4 + 2H 3 O. If the water is not withto
;
drawn, combination ensues between the fluoride and hydrogen or H.2 SiF 6 , named refluoride, with formation of 4 spectively hydroborofluoric, and hydrosilicifluoric acids
HBF
thus:
B
2H 9 SiF 6 + H 2 SiO 3
.
These compounds
ionise into
H-
MODERN CHEMISTRY
60
ions,
are
and the complex ions BF 4 and SiF and many salts in which metals replace the hydrogen. They f)
;
known
are similar in kind to potassium aurichloride.
The other halides of boron and silicon, and also of phosphorus, sulphur, selenium, tellurium, and iodine, react at once with water, forming hydrogen halide and an The
acid.
equations are as follows
:
= BCl 3 + 3 H 2 O.Aq = SiCl 4 + 3 H 2 O.Aq PCL + 3 H 9 O.Aq = = PCl 5 + 4 H;O.Aq 2S Cl 2 +2H 2 O.Aq =
B(OH) 8 .Aq+3HCl.Aq; 0=Si(OH) 9 + 4 HCl.Aq; P(OH) 3 .Aq+ 3 HCl.Aq; O=P(OH) 3 .Aq+5HCl.Aq; 0=S(OH) 2 .Aq + 4 HCl.Aq; + 3S; 2TeCL + 3 H 9 O.Aq = O=Te(OH) 9 .Aq + 4 HCl.Aq (7
3
H
2
O.Aq .Aq
= O=S(OH) 2 .Aq + 4 HCl.Aq; - 3 HIO 3 .Aq+i 5 HCl.Aq + I 2
.
It is to be noticed that where a hydroxy-compound corresponding to the halide is capable of existence, it is formed ; if not, excess of the element is set free. Hence
none of these halides can be prepared by acting on the hydroxide with a halogen acid they are all made either by the direct action of the halogen on the element, or by what comes to the same thing, the action of the halogen on a strongly heated mixture of the oxide of the element with carbon. Boron, silicon, and phosphorous chlorides are volatile liquids ; they fume in the air owing to their action on the water-vapour. S 9 C1 9 is a yellow liquid when saturated with chlorine at a low temperature, SC1 2 and SC1 4 are successively formed ; but on rise of temperature they dissociate into the lower chloride. IC1 is a black solid, converted by excess of chlorine at a low temperature into IC1 , a yellow solid, which easily dissociates into 3 IC1 and C1 9 and PC1 5 is a pale yellow solid, volatile at ;
;
;
a high temperature in a perfectly dry atmosphere without
THE HALIDES dissociation, but resolved
PC1 3 and C1 2
by the
61
least trace
of moisture into
.
Valency of Elements.
We
may remark
here the
gradual increase of valency as we pass from left to right in the periodic table. Lithium is a monad, with its congeners ; the elements of the beryllium group are dyads ; boron a triad
;
carbon a tetrad
as triad
;
sulphur, as a
and Moissan has
phosphorus acts as pentad as well pseudo-monad, a dyad, and a tetrad ; ;
lately
shown
that sulphur burns in fluorine,
forming a very stable hexafluoride, SF 6 while iodine forms a monochloride and a trichloride, and probably also a pentafluoride and a heptafluoride. Passing back to the boron group, if it is desired to form ;
anhydrous chloride, it is necessary either to heat the element, or its oxide mixed with charcoal, in a current of chlorine, or, except in the case of boron, to prepare a double salt of the chloride with ammonium chloride, and to volatilise the latter after
driving off the water
;
the aqueous chlorides
formed by dissolving the oxides or hydroxides in hydrochloric acid. Thallium forms monohalides, sparingly soluble in cold water, and thereby attaches itself to the
are
copper group.
Almost the same remarks apply to the elements of the carbon group ; solutions of the chlorides, with exception of those of carbon and silicon, are obtained from the element and hydrochloric acid or from the hydroxide, and they cannot be dried without reacting wholly or partially with water. For instance, titanium chloride, on careful addition of water, can become ClTi(OH) 3 , Cl 2 Ti(OH) 2 , Cl 3 Ti(OH), all of which are intermediate products between the tetrachloride and the tetrahydroxide ; such compounds are termed "basic chlorides." Anhydrous stannic chloride is
a fuming liquid,
formed by the
distillation
of a mixture of
the metal with mercuric chloride or by heating the metal in a stream of chlorine. Lead tetrachloride is a very
HO
unstable liquid, formed from the tetracetate, Pb(C it into the double ammonium salt
by converting
3
2 ) 4,
with a
MODERN CHEMISTRY
62
mixture of
ammonium
chloric acid; this salt,
chloride and concentrated hydrothen decomposed , is
(NH 4 ).,PbCl
r)
by concentrated sulphuric acid, when the tetrachloride It at once decomposes into separates as a heavy liquid. PbCl 9 + C1 on warming hence PbO 2 when warmed ;
,
with hydrochloric acid, undergoes the change
:
PbO +
4 HC1. Aq = PbCU + Aq + C1 2 Tin and lead resemble elements of the zinc group .
acid the dichloride
in
On
forming dichlorides.
dissolving tin in hydrochloric formed ; and a solution of the tetra-
is
chloride, when exposed to the action of nascent hydrogen, This action may be thus foryields the lower chloride.
mulated
:
Sn
C1 4 .
Stannous chloride
Aq + 2H =
SnCl,. Aq
+ HCl.Aq.
with water of crystallisation. Lead dichloride, on the otherhand, is sparingly soluble in cold water ; it is formed when a soluble lead salt, such as the nitrate, is mixed with the solution of a chloride: Pb(NO 3 ) 2 .Aq + 2NaCJ.Aq = PbCl 2
+ 2NaCl. Aq.
a white, soluble
is
The
salt, crystallising
bromide and the iodide are also
sparingly soluble, and are similarly produced. With arsenic and the remaining members of that group we may notice the same characters : the anhydrous chlorides
produced by the action of chlorine on the element, or, when it is not available, on a mixture of the oxide with carbon at a red heat ; the aqueous solution produced by dissolving the oxide or hydroxide in hydrochloric acidBasic chlorides are also known, e.g. ClAsO, CISbO, and the trichlorides ; and OPC1 3 , and OSbCl 3 ,
ClBiO, from
from the pentachlorides, on reacting with
a small
amount
of water.
Mass* Action. tity
of a
compound
The in unit
action of mass, that is, the quanvolume, is well illustrated by the
action of water on antimonious chloride. salt in
HO
=
OSbCl + (n + 2)HC1. Aq. + 2 the increase in the number of molecules of water
SbCl 3 .nHCl.Aq
Here
A
solution of this hydrochloric acid gives a precipitate on adding water r
THE HALIDES
63
causes the precipitation of the basic chloride ; on adding more hydrochloric acid, however, so as to increase its active mass, the reaction is reversed, and the precipitate redissolves
H ,O. stable
SbCl 3
:
OSbCl+
Above
S
;
(n
+ 2)HCl.Aq= SbC! 8 .Aq.nHCl +
a certain concentration of water
SbOCl
is
above a certain concentration of hydrogen chloride,
.
The
higher halides of
molybdenum, tungsten, and
uranium, themselves prepared by the
action of halogen on
the element, yield tue lower halides on heating. They are volatile, coloured bodies, soluble in water ; the higher ones are decomposed by water.
The
elements
chromium, manganese,
cobalt,
iron,
and nickel, although not all belonging to the same series, show, nevertheless, a gradation of properties. The dihalides of all are known in the dry state ; they are most readily obtained by heating the metal in a current of hydrogen halide, if required lised with water,
anhydrous
;
or if in solution or crystal-
by dissolving the oxide or carbonate in the halogen acid and evaporating until crystallisation ensues. As examples: Fe + 2HCl = FeCl 9 + O MnCO 3 -h
H
2 HBr.
The
Aq = MnBr 2 Aq + H.O + CO 2 .
;
.
trihalides are best made by heating the elements of halogen, if required anhydrous ; if in solution, by dissolving the oxide or hydroxide in the halogen acid. The trihalides of manganese and cobalt are very unstable ; and if the corresponding oxides be treated with halogen acid, a portion of the halogen is evolved, thus : in a current
Fe,O 3 + 6HCl.Aq = 2FeCl 3 .Aq + 3 H O Mn.,O 3 + 6HC1. Aq = 2MnCl 3 Aq + $H.). But MnCJ 3 .Aq gradu;
ally
decomposes, especially
if
temperature
2MnCl 3 .Aq=2MnCl 2 .Aq4-CJ 2
.
And
if
is
raised, thus
MnO
2
be
:
em-
evolved from the outset : 2MnO 2 -fthe MnCl 3 decomposing further on standing or on rise of temperature.
ployed, chlorine
is
8HCl.Aq=2MnCl 3 .Aq + 4H O+Cl,;
With Co 2 O 3
a transient
brown
coloration
is
noticeable
on
adding hydrochloric acid, implying the momentary forma-
MODERN CHEMISTRY
64
CoCl 3 .Aq
tion of
and
;
but
it is
at
once resolved into CoCl 2
.
Aq
free chlorine.
Oxidation and Reduction. As already remarked, the raising of the valency of an element is often spoken of " as " oxidation ; the reducing of the valency, as " reduction." The tendency of chromous halides to transform into
chromic compounds
to expose
them
is so great, that it is not possible to air without the change taking place,
and consequently the reduction of chromic compounds to chromous is a difficult operation. But with iron, both classes of compounds have nearly equal stability ; hence oxidation and reduction play a great part in their formation. The action of nascent hydrogen from any source reduces halide into ferrous:
ferric
FeCl 3 .Aq +
H = FeCl.,.Aq +
HC1. Aq.
Similarly, a ferrous halide, in presence of halogen acid and either free or nascent oxygen, is oxidised to a ferric
2 FeCl 2 .
:
Aq + 2 HC1. Aq + O = 2 FeC! 3 Aq + H 2 O. .
Or
the halogen itself may be used to effect the change : 2FeCl .Aq + Cl 9 =2FeCl 3 .Aq. On evaporating these solutions, hydrolysis takes place partially ; thus ferric chloride yields
character, such as are partly hydroxide, statement applies to the halides of all
compounds of
a basic
(OH)FeCJ,, (OH),FeCl, which partly chloride. these metals.
This
Colour of Ions. The triad and dyad ions in the case of these metals exhibit remarkable differences of colour. Thus chromous ions are blue, chromic, green ; basic ferric ions are orange-yellow, ferrous, pale green ; manganic, brown, manganous, pale pink ; cobaltous, red, and nickelous, grassHence a change in the ionic charge of the metallic green. ion
is
accompanied by a striking colour-change. halides of the palladium and platinum groups
The
of metals closely resemble in character those of gold, which have already been described. The dihalides of the palladium group are all soluble, save PdI 2 , which is prepared by precipitation with potassium iodide. Nitro-hydrochloric acid yields the higher chloride ; it remains on evapo-
HALIDES OF COMPLEX GROUPS ration. salts, e.g.
65
These form with chlorides of the alkalies double RuCl s .2HCl, RhCl 3 .2HCl, and PdCl 4 .2HCl; + +
KK
are probably ionised as and PdCl 6 , &c. Chlorine also acts directly on red-hot metals of the platinum group, forming a mixture of chlorides ; these, on heating, lose Solutions of the halides chlorine, giving lower chlorides. can also be prepared by the action of the halogen acid on
the latter
the respective oxides. On heating to a high temperature, these halides are decomposed into the metal and halogen.
all
K
The compounds 2 PtCJ 6 and (NH 4 ) 2 PtCl 6 require special mention ; they are orange salts, nearly insoluble in water, and are used as tests for potassium and ammonium, and also as a precipitant in estimating these ions. Their existence is probably to be ascribed to the power possessed by chlorine of sometimes acting as a triad, and the structural formula is be-
KCl=Ck lievedtobe
NH Cl=Ck
/Cl
/Cl
4
/Pt\x and ci KCI-CI;
NH4o~Gr
>Pt<^
x ci
.
of certain complex groups are also known. these contain oxygen or hydroxyl, (OH), they are generally termed basic salts or halo-acids ; they will be Halides
When
The others may be divided into two considered later. those like ammonium halides, and those derived classes :
from hydrocarbons. Ammonium and phosphonium halides. These halides, which are formed by direct addition of the hydrogen halide to
ammonia
or to phosphine, closely resemble in and in reactions, the
colour, in crystalline form (cubic), halides of the lithium group of metals.
On
mixing a solution
of ammonia and hydrochloric acid, for example, the combina= tion occurs: and on 3 .Aq + HCl.Aq 4 Cl.Aq ;
NH
NH
ammonium chloride From the conductivity
evaporating the solution to dryness, left
an anhydrous
in
ammonia
solution,
NH^OH written
VOL.
:
in
it is
known
4
is
of
amount of and the equation may be
to contain a certain
an ionised condition
NH OH.Aq
II.
state.
;
+ HCLAq =
NH Cl.Aq 4
+ E
H
2
O.
MODERN CHEMISTRY
66
As the hydroxyl ion is removed from the solution by the formation of practically non-ionised water, more and more ammonium hydroxide is formed to maintain equilibrium between OH. Aq and the whole is ultithe and the 4 3 Aq The rate of transformation, however, mately transformed. Combination has been shown not to is a very rapid one. take place between perfectly dry ammonia and dry hydrogen chloride ; hence it does not seem unlikely that ionisation may occur, either in the gaseous state, or more probably on the surface of the vessel in the condensed layer of moisture which appears always to adhere to all solid surfaces. Once started, combination occurs continuously until the reaction is complete. Ordinarily "dry" ammonia, however, at once gives a dense cloud with hydrogen chloride, bromide, or
NH
NH
.
;
Again, perfectly dry ammonium chloride has the
iodide.
vapour-density 26.25, corresponding to the molecular = 4 + = 35.5) = 53. 5; whereas, if 14 + weight 4 moist, the density is half that amount, corresponding with = 1 7 and HC1 =36.5. These compounds a mixture of 3 have densities of 8.5 and 18.25 respectively, and a mixture in equal proportions of each has a density the mean of
H
(N=
NH
the two, viz., 13.125.
It appears necessary that ionisation
+
into
NH NH
NH 3
4
and
and Cl should take place before dissociation into
HC1
C1 can 4
is
possible.
volatilise
The
electrically neutral
+
unchanged
;
the ions
NH
4
body
and Cl
are incapable of volatilisation as such, and in volatilising unite their opposite charges, and form the two electrically
NH
compounds HC1 and g Phosphine, PH 3 also unites with hydrogen chloride,
neutral
.
,
but only under high pressure, at the ordinary temperature. On the other hand, phosphonium iodide, is 4 I, pro-
PH
duced by the union of phosphine with hydrogen iodide under
it forms white, cubical atmospheric pressure ; which, like ammonium chloride, dissociate when heated. The hydrides of arsenic and antimony form no such compounds.
crystals,
PHOSPHINE GROUPS
67
must be assumed that these compounds are formed the with change of valency of the nitrogen or phosphorus IH V becomes triad becomes pentad ; the C1. On 3 4 distilling with sodium hydroxide or slaked lime, water is formed, and the element is reduced to its original triad conIt
NH
thus:
dition,
NaCLAq,
4
;
HN
N H
Cl.Aq + NaOH.Aq =
NH OH.Aq + 4
NH 4 OH.Aq = NH 3 + H 2 O.Aq,
and
two
electrically neutral bodies.
Carbon shows no such tendency
to change valency. " saturated," hydrocarbons of the methane series are have take i.e. no to other element. tendency up any they Hence halogen must replace hydrogen. This can be done either directly, by the action of the halogen on the hydroC1 2 = C1 + HC1 or carbon, as, for instance, 3 4 + the the action of halogen acid on the hydrindirectly, by C1 + oxide O. Such hydr+ HC1 = 3 3 2 that derived from ethane, oxides are termed alcohols C 2 6 , is the ordinary anhydrous alcohol of commerce ; its formula is C.7 5 OH, and the corresponding chloride of It will be remembered that the strucethyl is CJHLC1.
The
CH
:
CH OH
;
H
;
H
tural
CH
CH
H
formula of ethane
ethyl chloride
is
H\
is
H-^C
H/
H\
H-^C
H/ /H CP-C1. \H
/H
C^-H,
\H
There
and that
is,
of
however, a
difference between the formation of ethyl chloride, for Whereas sodium chloride example, and of sodium chloride. is
ionised in solution in water, ethyl chloride is insoluble, is therefore non-ionised. Hence the action is a slow
and one
;
the
allowed
to
alcohol
stand
is
for
with hydrogen chloride, some hours, and distilled ethyl
saturated
;
chloride, being volatile, passes over ; it is a gas, condensing at about 12 to a mobile colourless liquid. It is probable that the hydrogen chloride is ionised in solution in alcohol ;
the alcohol
is
also
possibly ionised
to a
minute extent
;
MODERN CHEMISTRY
68
water
is
formed by the union of the hydrogen and hydroxyl
+
ions,
and non-ionised ethyl chloride
+ HC1. Ale =
H O + C.,H 2
C1. 5
distils
But
over
this
:
C.7
H OH 5
suggestion,
it
must be admitted, is somewhat speculative, and is based only on analogy with reactions of a more familiar nature. The formation of some of the halogen compounds of the olefines, and of hydrocarbons of the acetylene and benzene series, has already been alluded to on p. 48.
CHAPTER
IV
" Insoluble Substances" Indicators Preparation of Basic Oxides Properties of the Basic Oxides and Hydroxides-
Hydroxides and Acids
The " Solubility- Product ' Basic Sulphides Oxides and Hydroxides of Complex Groups: Alcohols, Aldehydes, Ethers; and Sulphines, Amines and Phosphines. '
The Oxides and Hydroxides, Sulphides and Hydrosulphid.es, Selenides and Tellurid.es. Owing to the dyad valency of oxygen, sulphur, selenium, and tellurium, compounds of these elements are more numerous than those of the halogens. And whereas double halides of hydrogen and other elements are not numerous, SiF 6 , being confined to such bodies as 4 , H,PtCl c 2 and a few others, those of the oxides are very numerous, " and form two important classes, the " hydroxides and " the acids."
H
Hydroxides and Acids. classes
may be regarded
one atom of hydrogen,
HBF
Members of both
in
these
water minus combination with elements,
as hydroyxl, that
OH,
,
is,
but they differ radically in that the true hydroxides ionise
+
into element
+++
Bi (OH) 3
and hydroxl, thus: ;
whereas acids
H
SO 4 .Aq, 69
-
:
and
.Aq,
hydrogen- and a + + HOCl.Aq, 3 .Aq,
ionise
negatively charged radical, thus
H(HSOJ.Aq,
++
-
NaOH.Aq, Ca(OH) into
HNO
many
others.
There
MODERN CHEMISTRY
70
hydroxides in which the ionisation may take " such compounds are said to be either " basic " " acid or according to circumstances ; thus, aluminium
are
certain
either
form
;
A1(OH) 3
hydroxide, it
reacts
in
the
3HCl.Aq = Al
is
,
basic;
with hydrochloric
following
acid
-
+++
Al(OH) 3 .Aq +
manner:
3H 2 O; on the other hand, when caustic soda is presented to aluminium hydroxide, it forms sodium aluminate, NaAlO 2 .Aq, a derivative of the acid HAlCX.Aq, which is formed from A1(OH) 3 by loss of O. The ions in the water "A1(OH) 8 = O=A1OH + 2 Cl 3 .Aq+
H
:
+
latter case are
H
and
HA1O 2
between
A1O 2
and
,
and the reaction takes place
NaOH,
NaOH.Aq-NaAl6 2 .Aq + H 2 O.
It
case that
the acids are derived from
have
a portion
lost
are, like
O=A1OH,
HAlO
thus: is
2
.Aq +
generally
the
hydroxides which
of their hydrogen as water.
They
partly oxide, partly hydroxide.
"Insoluble Substances." The hydroxides are, with some exceptions, generally spoken of as insoluble in The word " soluble " is a relative term it is water. ;
probable that very few, if any, substances are absolutely Silver chloride is usually regarded as wholly insoluble. insoluble in water, but pure water shaken up with that salt acquires increased conductivity, showing that some chloride
In one of the equations must have gone into solution. given above, A1(OH) 3 is followed by "Aq," implying This method that it is dissolved and ionised in solution. of writing is perfectly correct for the portion which is dissolved, but that constitutes only a very minute fraction of
What is dissolved, however, Is ionised and enters into reaction, and when it has been removed, as in the equation given, with formation of practically non-ionised the whole.
water-molecules, its place is taken by more equilibrium tends to establish itself between the dissolved portion and :
HYDROXIDES AND ACIDS the portion remaining undissolved.
common
excess of
of water
salt
be placed
at
We
know
71
well that if
the bottom of a vessel
will not all dissolve, but, as the dissolved portion diffuses away into the upper layers of water, its place is it
taken by fresh salt, which dissolves, until, if sufficient time be given, the whole solution becomes saturated with salt. as ions, it may Similarly, the removal of the aluminium and of the hydroxyl of the aluminium hydroxide,
be
as water, on treatment with an acid, causes a 3, fresh portion of the hydroxide to go into solution, and this continues to go on until all has undergone reaction.
A1(OH) The
hydroxides of the elements may be classified like the analogy between the formulae is seen on ; comparing the tables on pp. 72, 73, with those on p. 50. Oxygen compounds of fluorine are wanting. the halides
[C1(OH) 7 ],
[OC1(OH) 5 ], [02 C1(OH) 3], 3
C1(OH),
[C1 2
7 ].
MODERN CHEMISTRY K
ffi
:O
:
:O
gf
If
8
E
ffi :
:O
o
i
iO.
:
:EO OS"c
o;
a"
-scr
-^;3-
oo<
oow
:^ffi
^-T
s O
'to:
ox
C^j.^
,J5
'SO
:
O
:
ffi
!
:
:
N
N9 ON
Ou
:
19 UU o
O
-c:-
H9 OH
uo OU
:
| C/31
^ rt
rt
CQ33
:
=9
U
'% OH
OXIDES AND HYDROXIDES
73
MODERN CHEMISTRY
74
SO 2 and MoO 2 ; but manganese also forms O g Mn(OK), termed potassium permanganate, which is analogous in formula as well as in crystalline form with potassium perchlorate,
O
3
It
C1(OK).
convenient, however, also to include in the iron group of elements.
is
chromium and manganese Cr(OH) 3
OCr(OH) Cr2O 3
Cr(OH) 2
Mn(OH) 3 Fe(OH) 3 OMn(OH) OFe(OH) Mn2 O3 Fe-A Mn(OH) 2 Fe(OH) 2
MnO
CrO
FeO
Ni(OH)3
Co(OH) 3
Ni 2 O 3
Cc^Og
Ni(OH) 2
NiO
Co(OH) 2
CoO
Elements of the palladium group have a very wide range hence they form a large group of compounds.
of valency
;
O2 Ru(OK) 2
RhO 3 Rh(OH) 4
...
Pd(OH) 4
Ru(OH) 4
RhO2
RuO2
Rh(OH) 3 Rh 2 O 3
Ru2O 3
PdO2
OsO 4
IrO 3
OsO2
Os(OH) 4
Ir(OH) 4 Pt(OH) 4 PtO2 IrO2
Os2O3
Ir 2
OsO
IrO
O2 Os(OH) 2 O2 Ir(OK) 2
Ru(OH) 3
RhO
...
Pd(OH)o
RuO
PdO
O3 Pt(OH) 2 PtO
The hydroxides of lithium, sodium, potassium, rubidium, and caesium are all soluble white compounds, melting to colourless liquids at a red heat. They do not lose water, even at the highest temperatures, hence the oxides cannot be prepared from them ; indeed, the oxides are produced only by the action of the metal on the hydroxide, at a high temperature ; for instance, aNaOH + 2Na = Na + 2 . They are white, non-crystalline substances, combining at once with water to form the hydroxides Na 2 + 2 = 2NaOH. The hydroxides are prepared from the carbonates by boiling a solution with Na 2 slaked lime (calcium hydroxide) 3 .Aq +
O
O
H HO
CO
:
Ca(OH),.Aq = 2NaOH.Aq + CaCO 3
;
or
by heating
redness a mixture of the carbonate with ferric oxide, the ferrite is formed Fe 2 3 = 2 + 2 3 + :
On
K CO
O
2KFeO
treatment with water, potassium ferrite thus: 2 2
is
to
when
CO
2
.
decomposed,
KFeO +2H O.Aq=KOH.Aq + Fe(OH) 3
.
INDICATORS
75
In either case, the solution of hydroxide is evaporated to dryness in an iron vessel and fused. These hydroxides are said to be basic, for they are neutralised
chloric
by
acids,
forming
salts.
Thus, with hydro-
KOH.Aq + HCl.Aq = KCl.Aq + H 2 O,
acid, the point of neutralisation
that
is,
when
the acid and base
are present in theoretical quantity to form the salt and water " indicator." is determined by the addition of an
The most important indicators are litmus, Indicators. Litmus is a weak phenol-phthalei'n, and methyl-orange. acid, red in colour, the salts of which are blue. dissolved in water, the molecule is hardly at all ionised, If a base hence the red colour of the acid is alone visible.
When
such as sodium hydroxide
is
in
added, which,
aqueous solu-
+ is largely ionised into Na.Aq and OH.Aq, the hydroxyl ions combine with that portion of the hydrogen ions of the litmus acid which exist in solution ; when these are withdrawn, more hydrogen ions take their place, and the
tion,
solution acquires the colour of the ion of the litmus acid, Conversely, if an acid be added to a base in
viz., blue.
which the blue litmus
ions are present, the
hydrogen ions of
the acid combine with the hydroxyl ions of the base, forming water, so long as any are present ; after they are all in combination they convert the ion of the litmus acid into the
red acid, non-ionised, and there is a marked colour-change. As the colours of the litmus acid and of its ion are both
very bright, the presence of a mere trace of the indicator suffices.
that
is,
Phenol-phthalei'n, like litmus, is also a weak acid, hardly ionised at all in dilute solution ; the acid
it is
colourless, but the ions are pink, hence the addition of a trace of free alkali causes the colourless solution to become is
But this indicator gives results only with strong bases, pink. like the hydroxides of the alkalies ; with ammonium hydroxide, present in a solution of ammonia in water, it is not a
good
indicator, for
NH OH 4
is
too
weak
hydroxyl and ammonium ions are present
in
a base,
I.e.
the
too small amount
MODERN CHEMISTRY
76 to liberate the
ions of the phenol-phthalein, unless much Hence the is present in solution.
ammonium hydroxide
presence of a trace of free ammonium hydroxide is not revealed by that indicator. Phenol-phthalein is therefore serviceable only with strong bases, but it may be used for
weak
Methyl-orange, on the other hand, is a comwith a weak base it forms the ions and it may therefore be used for weak bases like
acids.
paratively strong acid
of a
salt,
;
ammonium hydroxide,
or for strong bases like the
ides of the alkali metals
hydrox-
too strong an acid to serve well as an indicator of excess of a weak acid, such as carbonic or acetic acid.
;
but
Its
it
is
colour-change
is
from orange
to orange-pink.
Preparation of Basic Oxides.
The
hydroxides of
the metals of the sodium group, as already mentioned, do not lose water on heating, and the oxides, therefore, cannot
be thus obtained. Neither do their carbonates lose carbon dioxide, nor their nitrates oxides of nitrogen, save at an imBut all other basic oxides may be practicable temperature. prepared by heating the hydroxides, carbonates, or nitrates of the metals, and a few may be obtained by heating the sulphates.
Calcium and strontium oxides
are generally
prepared from the carbonates, which are found as minerals, named limestone and strontianite respectively. The opera" tion of preparing " quicklime or calcium oxide is techni" but called Alternate layers of burning." cally, wrongly, lime and coal are placed in a tower of brick or stone, termed a limekiln the coal is set on fire, and its heat CaCO 3 = expels the carbon dioxide from the carbonate ;
:
CaO-fCO.,.
If calcium carbonate be heated in a closed
however, so that the carbon dioxide does not escape, the dissociation proceeds until the amount of carbon dioxide in the vessel has reached a certain proportion, which is perfectly definite for each temperature, or until the carbon vessel,
dioxide has attained a certain " concentration." The reaction then stops. But if the carbon dioxide be removed as it is formed, the reaction goes on to the end, until all carbon
BASIC OXIDES
77
The draught in the kiln removes the dioxide has escaped. Stroncarbon dioxide, hence the product is calcium oxide. tium carbonate is causticised in the same way as limestone ; but the temperature for witherite
high
;
baryta
Ba(NO 3
;
)
is it
(BaCO 3 ) is inconveniently consequently prepared by heating the nitrate, may be supposed to split into BaO and
the latter, however, decomposes even at moderate and hence the equation is : ; temperatures into 2 . These oxides are +4 3 ),= 2 + 2
N.,O 5
;
NO
2BaO
2Ba(NO
O
NO
O
whitish-grey solids, volatile at the temperature of the electric arc, and combining with water with great rise of tem-
The hydroxides are solperature to form hydroxides. barium hydroxide most, calcium least. uble in water aqueous solution of the former deposits crystals of a hydrate,
An
Ba(OH) 2 .8H 2 O. The
sparing solubility of calcium hydroxide makes it possible to precipitate it by the addition of caustic alkali to a soluble salt of calcium, provided too much water is not pre= Ca (OH), + zNaCl.Aq. sent : CaCl 2 .Aq +
aNaOH.Aq
Of course,
a saturated solution of calcium hydroxide remains, hence the precipitation is not complete. This plan is applicable to the preparation of all hydroxides which are insoluble in water, unless they dissolve in excess of the caustic alkali ; " acid " if they do, they are said to display properties.
Beryllium and magnesium hydroxides are thus precipitated
MgCl 2 .Aq + 2KOH. Aq = Mg(OH) 2 + 2KCl.Aq.
:
The
hydroxide may be filtered off and dried, and the white mass, on ignition, leaves the oxide as a white powder. By this means, too, the hydroxides of copper (cupric, Cu(OH) 2 ), silver,
AgOH,
zinc,
Zn(OH),, cadmium, Cd(OH) 2
,
aluminium, A1(OH) 3 , scandium, yttrium, lanthanum, and ytterbium, gallium, indium, and thallium, with similar formula?, titanium, zirconium, thorium, with formulae
OM(OH)
2,
(where
M
stands for an element of
Sn(OH) 2 and SnO .nH.,O), lead (plumbous, Pb(OH) ), bismuthous, Bi(OH) 3 chromic, Cr(OH) 3 and chfomous, that
group
;
germanium, tin
(stannous,
,
stannic,
,
,
MODERN CHEMISTRY
78
manganic and manganous,
ferric and ferrous, , cobaltous and nickelous in short, from all elements which " And from almost all these the form " basic hydroxides. oxides may be obtained by heating the hydrates to redness. Excess of the precipitant, however, must be avoided in many cases, for some of these hydroxides display acid properties
Cr(OH) 2
:
if in Thus, for example, if presence of excess of alkali. excess of sodium hydroxide or potassium hydroxide be added to the solution of a soluble salt of zinc, such as the
chloride, nitrate, or sulphate, the first change, as already shown, is the precipitation of the hydroxide ; but on additi Dn
of excess of
alkali, the
precipitate redissolves, forming the
+
compound
ZnO 2 it is
;
Zn(OK) 2 .Aq,
this
compound
insoluble.
It
is
is
of which the ions are
+
K, K, and
thrown down by alcohol, in which named zincate of potassium.
generally
Cadmium
forms a similar compound, but that of aluminium OAl(OK) ; the hydroxide, A1(OH) 3 , on losing water is transformed into the condensed hydroxide, OAl(OH), which may be termed aluminic acid, of which
has the formula
the hydrogen atom
is Stannous exchangeable for metals. and plumbous hydroxides dissolve in excess of alkali, doubtand chromic less forming compounds similar to that of zinc hydroxide is soluble in cold solution of caustic alkali, forming, no doubt, a compound analogous to that of aluminium but it is decomposed on warming, with reprecipitation of the ;
;
The hydroxides of all these elements may also hydroxide. be precipitated by a solution of ammonium hydroxide, and some of them are redissolved ; but the compounds formed are of a different nature from those described in the case of zinc, &c., and will be afterwards considered.
As
Properties of the Hydroxides.
regards the
properties of the hydroxides, that of copper (cupric)
is
light
and of silver, brown chromic hydroxide is greygreen, and chromous, yellowish ; manganic, brown, and manganous, very pale pink ; ferric, rust brown, and ferrous, white when pure, but usually dirty green cobaltous, dingy blue,
;
;
PROPERTIES OF HYDROXIDES
79
The others are all white red, and nickelous, grass-green. amorphous bodies, and they all yield oxides on heating. even when boiled with water the Cupric oxide is black Argentous hydroxide loses water and changes colour. ;
oxide
brown
is
;
when heated
to redness
when hot and white when cold brown
powder
;
the
oxides
it
loses
oxygen, yellow cadmium oxide is a
Zinc oxide
leaving a residue of metallic silver. ;
of
aluminium,
is
scandium,
yttrium, lanthanum, ytterbium, gallium, and indium, and of titanium, zirconium, thorium, germanium, and stannic oxide are white powders ; thallium oxide is a yellow powder ; tin
monoxide
is a black powder ; that of lead (litharge, massia yellow substance, fusible at a red heat ; bismuth sesquioxide is a yellowish powder ; chromic, ferric, and
cot)
is
manganic are respectively green, rust-red, and brown ; chromous oxide is unknown, for any attempt to dry it results in the decomposition of water, the absorption of its oxygen by the chromous oxide which becomes chromic Ferrous hydroxide oxide, and the evolution of hydrogen. can be dried, but only with rigid exclusion of air it is a black powder. Manganous oxide is greyish-green, cobaltous, olive-green, and nickelous also greyish-green. Manganous hydroxide must also be dried in absence of air. These hydroxides and oxides are named bases. There ;
are some basic oxides, which are precipitated by adding a hydroxide, such as that of sodium, to a soluble salt, and to which there is no corresponding hydroxide. This is the case with the oxides of mercury. On referring to the table of halides on p. 50, it will be seen that the chloride of mercury has the formula HgCl This compound, .
commonly
called corrosive sublimate,
when
treated in solu-
with sodium hydroxide, gives a precipitate, not of HgCl Aq hydroxide, as might be expected, but of oxide tion
.
:
+ zNaOH.Aq = HgO + 2NaCl.Aq +
a
soluble
Hg (NO 3
)
mercurous salt, such on treatment with an
Q,
as
H
2
O.
Similarly,
mercurous
nitrate,
alkali gives a precipitate
MODERN CHEMISTRY
8o
mercurous oxide: Hg (NO .Aq + 2NaOH.Aq = Hg 2 O + 2NaNO 3 .Aq + H.,0. These are cases of relative
of
2
3)2
for, as has been already remarked, on boiling a from which cupric hydroxide has been precipitated, the blue hydroxide is changed into black oxide ; other hydroxides lose their water at a still higher temperature ; stability
;
solution
while those of the alkaline metals
may
be volatilised without
decomposing.
Oxides produced by Heating Carbonates. basic oxides may also be prepared by heating
Most of the
the carbonates, a class of salts afterwards to be discussed. The carbonates of the alkali metals, however, are not thus like their hydroxides, they may be volatilised ; But all other carbonates are dewithout decomposition. composed by exposure to a red heat. The process has already been described as a method of manufacturing quick-
decomposed
lime. Most carbonates, however, do not require the same And the high temperature ; a dull red heat suffices. oxides do not, as a rule, recombine with the carbon dioxide hence there is no danger of re-carexpelled, as does lime ;
bonating the oxide.
Oxides produced by Heating Nitrates.
The
of nearly all the basic metals, yield the respecThe tive oxides when they are heated to bright redness. nitrates of the alkali metals in this instance, as in others, do When heated they lose oxygen, not behave in this way. nitrates, too,
but only at a very high temperature, forming the nitrites, a class of salts afterwards to be described. Thus, potassium = nitrate undergoes the decomposition 2 + g :
O
2KNO
2KNO
The
product of heating the other nitrates, however, is the oxide, while a mixture of oxides of nitrogen is evolved. This may be supposed to take place in two stages : first, the nitrate may be imagined to decompose into the oxide 2
.
and nitrogen pentoxide, thus
:
Zn(NO 8 2 = ZnO + N 2 O 5 )
;
very easily decomposed by heat, and oxide of nitrogen: 2N 2 2 + 2 ; yields a lower while if the temperature is over 600, which is usually the
last
compound
is
O.=4NO
O
SULPHIDES AND HYDROSULPHIDES exceeded
81
decomposing the nitrates, the nitric peroxide is decomposed into nitric oxide and oxygen
in
partly further
:
2NO, = 2NO + O 2 NO, "and O 2
The
.
products, therefore, are
NO
2,
.
A
metal which forms two oxides, one containing more oxygen than the other, if the nitrate of the lower oxide is
Cases of this are mercury, and iron. Mercurous nitrate, carefully heated, gives, not mercurous oxide, Hg O, but mercuric oxide, HgO heated, yields the higher oxide. tin,
:
HgNO 3 - HgO + NO
2
;
similarly
Sn(NO 3 ) 2
yields
SnO 2
,
SnO and Fe(NO 3 ) 2 Fe 2 O 3 and not FeO. Oxides produced by Heating Sulphates. The sulphates require a higher temperature than the nitrates
and not
,
,
;
for their decomposition, consequently they are not generally But the equivalents of magused as a source of oxides.
nesium, zinc, and some other metals have been determined by estimating the weight of oxide obtainable on heating a weighed amount of sulphate ; and ferrous sulphate has been fireclay retorts for many years past at Nord" Nordhausen hausen, in Saxony, for the purpose of making S and red of oxide iron, Fe sulphuric acid," 3, 2 Oh., which, made in this way, has a fine colour, and is used as a distilled in
H
paint. is
not
When
a sulphate
is
heated, the gas
which escapes
SO 3 as might be imagined from the MgSO 4 = MgO + SO 3 the high temperature
entirely
equation:
O
,
;
decomposes most of the sulphur trioxide into the dioxide, SO 9 , and oxygen ; and the oxygen, in the case of ferrous
FeO into Fe 2 O 3 Sulphides and Hydrosulphides.
sulphate, oxidises the
.
The
analogy
between the elements oxygen and sulphur is well shown by comparing the sulphides of the elements of which the oxides have been described. Elements of the lithium group form both hydrosulphides and sulphides thus we ;
know sodium hydro sulphide, NaSH,
NaOH,
hydroxide the oxide
weak
acid
Na 9 O, ;
analogous to the similar in formula to
and sulphide, Na.7 S. Hydrogen
is a sulphide hence, on passing hydrogen sulphide through
MODERN CHEMISTRY
82
a concentrated solution of sodium hydroxide at 95 until saturation is complete, white crystals of NaSH.2H O 4>
+ deposit on evaporation.
The
equation
+ HSH.Aq = NaSH.Aq + H 2 O.
is
NaOH.Aq
:
On
mixing the solution with an equivalent quantity of sodium hydroxide and + evaporating, the sulphide is produced: NaSH.Aq-t-
+
-
+
- -
NaOH.Aq = Na 2 S.Aq + H 2 O.
Here it must be supposed that the hydrogen of the hydrosulphide is present as an anion, and that it reacts with the hydroxyl of the caustic soda, forming water, while the sodium sulphide remains in solution in an ionised form, and can be recovered on Similar compounds evaporation in crystals with 9H 2 O. exist with potassium. Calcium, strontium, and barium also form hydrosulphides and sulphides, analogous in formula to the hydroxides and oxides. They are similarly prepared to the sodium compounds, but, as the metals are dyads, their formulae are M(SH) 2 and MS; and there is an intermediate compound between the hydroxide and hydrohaving,
sulphide,
in
HSCaOH. They are
the
case
of
calcium,
also soluble in water.
the
formula
Magnesium,
too, forms a hydrosulphide, probably Mg(SH) 2 ; it is prepared by passing sulphuretted hydrogen into water in It is unlike the which magnesium oxide is suspended. hydrosulphides of the alkalies, for while they do not decompose with water, it, on the contrary, when its solution is heated to 80, reacts with water, yielding hydroxide
and sulphuretted hydrogen:
+
2H 9 S.
The
Mg(SH).,.Aq +
2HOH =
explanation of this change is that water is not wholly non-ionised, but that there are present some hydrogen ions ; these are not so inconsiderable in number, compared with those of the weak
Mg(OH)
acid
H
2
S
2
;
probable
on raising temperature, a certain amount of
hydrogen sulphide
is
liberated, and, being volatile,
it
escapes,
THE SOLUBILITY-PRODUCT
83
and is no longer present to act on the magnesium hydroxide and reconvert it into sulphide. Sulphides of boron, aluminium, chromium, and silicon are at once decomposed by water, and cannot, therefore, be
They are produced in aqueous solution. white substances formed by heating the elements to a high temperature in a current of sulphur vapour. The sulphides of copper, silver, gold, cadmium, mercury, indium, thallium, tin, lead, arsenic, antimony, and bismuth, and of the metals of the palladium and platinum groups, are all insoluble in water, or, to be more accurate, very sparingly
They form no
soluble.
Hence they are precipitated from soluble hydrosulphides. salts of these metals by addition of sulphuretted hydrogen ; form flocculent precipitates, usually characterised by striking colours, and are therefore generally used as a means of recognising the metal. CuS, Ag S, Au 9 S 3 , HgS, T1 2 S, T1 2 S 3 PbS, PtS 2 , and the othei sulphides of the platinum group of metals are black CdS, SnS 2 and ln 2 S 3 , SnS, and Bi 2 S g are brown, and As.7 S 3 are yellow
they
,
;
,
;
Sb.,S 3 acids.
is
These sulphides are not attacked by dilute orange. the other hand, the sulphides of zinc, manganese,
On
cobalt, and nickel are not precipitated by hydrogen sulphide, but they are thrown down by a soluble sulphide or hydrosulphide, such as those of ammonium or sodium. iron,
MnS
too, form flocculent precipitates ; ZnS is white, The reason of pink, and FeS, CoS, and NiS are black. the difference in the behaviour of the two classes of sulphides
They,
is
an interesting one, and will be
Solubility- Product.
now
explained.
been mentioned on p. 14 that the rate of chemical change depends on the amount of each of the reacting substances present in unit " volume. This last is generally termed the " concentration It has already
of these substances, for the more concentrated the solution the greater the mass present in unit volume. Now, if two
+ kinds of ions, such as
Na
and Cl, are present
in solution,
MODERN CHEMISTRY
84
necessarily in equal numbers, the solution will also contain a certain number of molecules of non-ionised NaCl, formed
by
and the relative number of ions and moledepend on the concentration ; the number of ions proportion to the number of non-ionised molecules will their union,
cules will in
For each dilutk greater, the greater the dilution. (and for each temperature) a state of balance will result; the position of this equilibrium will depend on the relative rate at which ionisation and union of ions to form molebe
cules go on ; if ionisation takes place twice as quickly as combinations of ions to form molecules, then two-thirds of the dissolved substance will exist as ions, the remainIf the solution is ing third being non-ionised molecules. made more concentrated by evaporation, the conditions are changed, and the rate of ionisation is reduced compared with the rate of union of ions with each other. Suppose that concentration be pushed so far that solid salt separates out ; the limit of concentration will be reached, since it is now impossible to alter the number of ions and of molecules The ratio will now remain in unit volume of the solution. constant, and if c and c be the concentrations of the ions (and they are, of course, equal), and if C be that of the non-ionised molecules, then c.c = k. C, k being a factor expressing the relative proportions of the non-ionised moleIf k is very small, then there are many molecules cules.
and few ions present if, on the contrary, k is large, the The expression ions are numerous and the molecules few. k.C is termed the "solubility-product." ;
To
A
case solution of ammonia in and OH, and of the ions 4 is it a partly of non-ionised molecules of 4 weak base that is, the number of non-ionised molecules In a solution conis much greater than that of the ions. taining 1.7 grams of ammonia per litre (one-tenth normal cent, of the total number of molesolution), only 1.5 per Hence a solution of ammonia, cules exist in the ionic state. unlike one of caustic soda or potash, gives no precipitate
water
take a specific
consists
partly
:
NH NH OH
;
INSOLUBILITY OF SULPHIDES of hydroxide relatively
when added
strong
a
of
solution
salts
of the
calcium, strontium, or With salts of the weaker base magnesia, produces a precipitate of magnesium
bases,
barium chlorides. however, ammonia
to
such
85
as
It is possible still further to reduce the ionhydroxide. of ammonia solution ; this can be done by the addition of an ammonium salt, such as the chloride, which, like most such salts, is The reason is, that highly ionised. isation
+
NH NH
= while (concentration of x (concentration of 4) k x (concentration of if more ammonium ions be 4 OH), added, the number of hydroxl ions will diminish by union
OH)
NH
non-ionised ammonium hydroxide, 4 ions, forming because the increase of the number of ammonium ions will increase the value of the product on the left-hand side of the
with
equation, and in order that it may balance that of the right, the relative number of molecules of must be in4
NH OH
creased
and we may see that
;
if
ammonium
chloride
is
added
magnesium chloride, ammonia solution will no longer produce a precipitate of magnesium hydroxide the ammonia is too weak a base, that is, it contains too few hydroxyl ions, which are the reason of its basic nature. Let us now return to the consideration of the insolubility of to
"a
solution of
;
sulphides of the copper group in acids and the solubility of such No substance, as has been before sulphides as that of zinc. remarked, is wholly insoluble in water ; zinc sulphide, however,
belongs to the very
sparingly
soluble
++
Hence for
the product
it is
small,
Now,
x/(S)
y.C(ZnS), which must that the compound is so
equal to
seeing
the ions of
ionisation
H
+
2
S
are
compounds.
has a very small value, necessarily be very
sparingly soluble.
+
H, H, and S
;
but though the
very small, hydrogen sulphide being a very weak acid, they are yet sufficient to reach the value of the very small solubility-product LC(ZnS). If, however, is
the concentration of the S-ions
is
still
further
diminished
MODERN CHEMISTRY
86
+ by -addition of some compound rich in H-ions, such as +-f + HCl.Aq, then the product c(Zn) xc'( S ) will be less than >.(ZnS), and there will be no precipitate or if hydrochloric acid be added to precipitated zinc sulphide, ;
it
On
be dissolved.
will
the other hand, the addition of
weak
acid, and poor in hydrogen ions, does not bring about solution of zinc sulphide ; indeed, the precipitation of zinc from a solution of its acetate by hydrogen acetic acid, a
sulphide
almost complete.
is
The
solubility-product of copper sulphide, and of the sulphides which are not soluble in dilute acids, is
other
still less
;
hence hydrogen sulphide precipitates them from
acid solution, for the concentration of the S-ions of the
hydrogen sulphide may be very much diminished without ++ the product
CuS is still less soluble in water than ZnS. Oxides and Hydroxides of Complex Groups. The oxides and hydroxides of complex groups show
for
analogy in their formulae, and often in their methods of few preparation with the basic oxides and hydroxides. instances of these will now be given. Ammonia (see p. 42) is very soluble in water ; at the ordinary temperature, no less than 800 volumes of the gas dissolve in one volume of water, forming a very pungently This solution consmelling solution named liquor ammonia. sists for the most part of a mixture of liquid ammonia with
A
water
NH
4
;
it
OH,
of the ions
probably also contains ammonium hydroxide, and, as already mentioned, less than 1.5 per cent.
+
NH
Hydrazme,
4
and
NH 2
OH. 4,
also
It
is,
therefore, a
forms a hydrate,
a fuming liquid with slight smell
weak
base.
N H OH, 2
5
(and consequently in all it boils at 119, and is probability fairly highly ionised) It has very corrosive, attacking wood, cork, and even glass. a strong reducing action, so that if added to a solution of ;
ALCOHOLS
87
which contains cupric
cupric sulphate
ions,
++ Cu,
gives an
it
immediate precipitate of cuprous oxide, Cu 2 O, nitrogen Like ammonia, it precipitates such hydrbeing evolved. oxides as that of aluminium, iron, &c. Hydroxylamine,
NH
2
OH,
is
a
somewhat
NO
similar body,
produced by passing
(see p. 97), through a mixture of granulated tin and hydrochloric acid, to which a little platinic chloride has been added ; the nascent hydrogen reduces nitric
the
oxide,
nitric
oxide
to
hydroxylamine
;
it
unites
with the
hydrochloric acid, forming hydroxylamine hydrochloride, OHC1. After removal of the tin by addition of 3
NH
sodium hydroxide and filtration, the solution is evaporated and mixed with alcohol ; hydroxylamine hydrochloride dissolves, while sodium chloride remains. solution
to dryness
of the base
NH
8
A
may be obtained by
addition of silver hydroxide
OHC1. Aq + AgOH.Aq = AgCl + NH 3 OH. Aq.
:
If
sodium methoxide (see p. 88) be added to a solution of the hydrochloride in methyl alcohol, the base is liberated, and can be separated from the alcohol by fractional distillation ; it is a volatile white solid. This compound is interesting, because the group is under no circumstances an ion ; its
OH
+
must contain ions of
solution in water since
it
3
and
OH,
ammonium hydroxide.
reacts like
Alcohols.
NH OH
The hydroxides
of
the
hydrocarbon
1 67, termed alcohols. Of these there are very many, but a few only will be chosen to serve as examples methyl alcohol, 3 OH, as types of ethyl alcohol, 3 2 OH, monohydric alcohols, which may be taken as the analogues of the
mentioned on
radicles are, as
p.
CH
:
CH -CH
CH OH 2
hydroxides of the monad
metals
;
glycol,
CH OH
,
a
2
dihydric alcohol, 1
A
special class of
are termed phenols. of these.
may be
likened
to
barium hydroxide,
such hydroxides derived from benzene, C H 6 " Carbolic acid," C 6 H 5 OH, is the best known ti
,
MODERN CHEMISTRY CH OH
88
2
Ba(OH)
and
;
glycerine
(glycerol),
CHOH CH OH
,
is
a
2
trihydric alcohol, as aluminium hydroxide is a trihydroxide. These substances differ from the hydroxides, however, by
being non-electrolytes, and therefore non-ionised. perhaps it is more correct to say that their conductivity of the same order of magnitude, but less in value, than
their
Or is
that of pure water.
CH
ample, 3 C1, as non-ionised
C
H
4
The corresponding halides, for exC1 9 , and C 3 5 C1 3 , are also regarded
H
they are practically insoluble in water. Nevertheless, methyl chloride has been transformed into methyl alcohol by heating with water to a high temperature = in a sealed tube under pressure C1 + 3 ;
CH OH + HC1 3
mides, may with silver
CH
2
CH
2
:
CH OH
Br
CHBr + 3 AgOH.Aq =
CH
HOH
and the others, but preferably the brobe similarly changed into hydroxides by heating hydroxide, or with silver oxide and water ;
Br
2
CHOH .Aq + 3 AgBr. CH OH
Is
it
2
possible that at a higher temperature the ionisation is sufficient (though it must be exceedingly small) to produce the interaction ?
The metals sodium and potassium dissolve in the alcohols, with evolution of hydrogen, forming compounds somewhat analogous to the hydroxides ; instead of hydrogen, however, they contain a hydrocarbon group : sodium methoxide, for example, has the formula Na(OCH ). Such sub3 stances are white solids, like caustic soda. Aldehydes. The alcohols, if oxidised by boiling them with chromic acid, yield a class of bodies analogous to the oxides, termed aldehydes + 3 2 - (CH 3 - CH)"O + H,O. It will be noticed that ethane, has lost two hydrogen atoms, and that the 3 3, CH.,, is now a dyad group, capable of comresidue, 3 The aldehydes are bination with an atom of dyad oxygen. volatile liquids, with strong odour, and those containing few :
CH
CH CH
CH CH OH O
AMINES AND PHOSPHINES
89
atoms of carbon are miscible with water. They form easily decomposable compounds with water, which are di-hydroxides
;
ordinary aldehyde forms CH.,
e.g.
\OH
When brought into contact they are called aldehydrols. with solutions from which hydrogen is being evolved, the aldehydrols lose oxygen, and are converted into alcohols :
/OH CH CH< + 2 H = CH -CH OH + H X)H 3
8
The is
O.
alcohols cannot be termed basic substances
evident that they
many
2
show analogy with the
;
still, it
true bases in
respects.
Amines and Phosphines. containing
Derivatives of nitrogen, and even of iodine and of oxygen, hydrocarbon groups, are however known,
which are
true
phosphorus, sulphur,
in
alcoholic
If ammonia bases, though weak ones. solution be heated with excess of methyl
tetra- methyl -ammonium + 4CH 3 I = N(CH 3 4 I + sHI.
iodide,
NH
3
)
iodide is formed This iodide, digested :
water and silver hydroxide, exchanges iodine for hydroxyl, and after removal of the silver iodide by filtration the solution may be evaporated to dryness. The residue is a white solid, of the formula ; 3)4 it is termed tetra -methyl -ammonium- hydroxide ; in
with
N(CH
its
reactions
having the
a
usual
it
OH
shows great analogy with caustic potash, taste, and producing precipitates with of the metals. In solution it is more
caustic salts
ionised than
ammonium hydroxide, though
less
than that
of potassium.
Phosphine, as remarked on hydrogen iodide, forming a salt,
p.
PH
66,
combines
with
phosphonium iodide, But as it is decomposed resembling ammonium chloride. and hydrogen iodide, an by water into phosphine, 3, ; attempt to convert it into phosphonium hydroxide, 4 Substituted phosphonium compounds, cannot be made.
PH
4 I,
PH OH
MODERN CHEMISTRY
90
however, are known,
which
in
a hydrocarbon radicle, such
Sodium and phosphorus methyl, replaces hydrogen. combine when heated together under an oil called xylene, forming PNa g ; this body, treated with methyl iodide, yields as
P(CH 3 )^; with more methyl iodide formed; and its solution in water, which is not decomposed by the solvent, yields with silver hydroxide tetra-methyl-phosphonium hydroxide, P(CH 3 ) 4 OH, a base resembling the corresponding ammonium compound. These compounds exist owing to the double valency of nitrogen and of phosphorus, which can function either as trimethyl phosphine,
P(CH
3)4
I
is
Double valency is to be noticed also with oxygen and with sulphur, although with the former tetrad combinations are far from stable, while with the latter both dyad and tetrad compounds can be formed. Ethers. Oxide of methyl and oxide of ethyl, which are usually named methyl and ethyl ethers, are formed by triad or pentad.
mixing solutions in alcohol of methyl or ethyl iodide with I. Ale + NaOCH Ale sodium methoxide or ethoxide 3 3 = Nal + 3 Ale. The ether has a low boiling3 point, and can be separated by fractional distillation from the alcohol in which it is dissolved. Methyl ether is a Such gas; ethyl ether a volatile liquid, boiling at 37.
CH
:
H COCH
.
.
compounds can also be prepared more readily by distilling a mixture of the alcohol with sulphuric acid, which yields SO,, hydrogen methyl sulphate, with the alcohol
HCH HCH
:
3
SO 4 + CH 3 OH
methyl ether
=
HgCOCHg +
and hydrochloric
CH
3
acid
?
SO 4
combine
.
at
Now, a
low
/H
x
/O\
temperature, yielding
H
CH/
;
but
it
is
impossible to
NCI
replace the chlorine by hydroxyl. Similar sulphur compounds, however, are stable. sulphide, produced
CH
slum sulphide,
Methyl by the action of methyl iodide on potas-
3
+
CH
KI
Kv
I
J>S
CHJ K/
=
KI
+
3
.
j>S,
CH/
unites
with
ETHERS
CH 3\ methvl iodide, forming
..
/ CH
/S\
CH/ M
c,i
3 >
a
compound con-
tetrad sulphur ; with silver hydroxide it yields corresponding tri-methyl-sulphonium hydroxide,
taining
the
C**3\
/CH 3
CH/ NDH From
iodine,
,
a
compound
too,
exhibiting basic properties.
iodonium compounds have been
prepared, in which the iodine functions as a triad
hydroxide with basic properties
is
known.
;
and a
CHAPTER V Neutral Oxides
Peroxides
Action of Nitric
Acid on Metals; on Oxidisable Substances Complexity of Oxides Spinels and Similar Compounds.
THE
properties of all chemical compounds show gradation ; is a slow transition from basic oxides and hydr-
and there
oxides, like those which we have been considering in the acid oxides and hydroxides. The transition
last chapter, to
takes place along two paths ; first, there are some oxides which are neither basic nor acid ; and second, a number of
oxides exist which are either basic or acid, according to
We
circumstances.
shall consider first the neutral oxides.
Peroxides.
In the potassium and calcium groups of When sodium is burned elements, peroxides are known. in air a light yellow powder is formed, sodium dioxide, of the formula Na.2 O 2 ; potassium yields a tetroxide, Both of these substances react with water, giving 2 4
KO
.
but if they are very slowly added to the water, ; so that the temperature does not rise much, a solution is obtained. The corresponding barium compound is formed off
oxygen
when barium monoxide
heated under pressure in air (see it forms a hydrate, probably Ba=O(OH) i.yH 2 O. On treatment with acid, hydrogen is formed ; and if dioxide, sulphuric acid be added 2 2, in theoretical amount to the barium dioxide, nearly insoluble barium sulphate is formed, along with a fairly pure solution of hydrogen dioxide: BaO=(OH) 2 .Aq p. 13).
On
is
addition to water
HO
92
NEUTRAL OXIDES +H
SO 4 Aq = BaSO 4 + O=OH 2 Aq.
It can
.
.
93
be purified,
and indeed obtained anhydrous by distillation under very low It then forms a somewhat viscous, colourless pressure. a sharp taste. liquid, with There is some doubt as to the constitution of hydrogen dioxide, and consequently of the dioxides from which it is It is unlikely that barium ever acts as a tetrad, derived. and much more probable that this character is to be attrihence the formula of its dioxide is more buted to oxygen and consequently likely to be Ba=O=O, than O=Ba=-O hydrogen dioxide has more probably the formula 2, than Indeed, hydrogen dioxide is possibly a weak acid, since the hydrated dioxides of calcium and barium are precipitated on addition of concentrated solutions of hydrogen dioxide to the hydroxides suspended in These substances have all bleaching power, for they water. readily part with their second atom of oxygen, and it is capable of oxidising coloured insoluble substances to colour;
;
O=OH
HO=OH.
less soluble ones.
Neutral Oxides, Class
I.
The
next neutral oxides
met with are carbon monoxide, CO, nitrous oxide, N 2 O, and nitric oxide, NO. These are all gases, but condense at low temperatures to colourless liquids, and at still
lower, freeze to white solids.
Carbon monoxide
is prepared by burning carbon in a supply of oxygen insufficient to convert it into the dioxide ; or by passing the dioxide over a layer of carbon, heated to redness. It appears that the monoxide is always the first
product ; for if moisture be excluded during the combustion of carbon in oxygen, the amount of dioxide relatively to the is very small ; and it is known that if water-vapour be absent, carbon monoxide cannot be induced to explode with oxygen. If even the minutest amount of moisture be present,
monoxide
on passing a spark the union takes place with explosion.
This
phenomenon is not easily accounted for it is readily repre= 2CO 2 + 2 O. sented by the equation 2CO + 9O + O 2 Can it be that at the very low pressure of the water-vapour
H
;
H
MODERN CHEMISTRY
94 a trace
is
ionised into
H and OH, and that the OH furnishes
CO, the hydrogen recombining with For it has re-form the molecule of water ? been found that no moisture is requisite to promote the union of oxygen and hydrogen if these gases be heated the oxygen for the to
oxygen
Phosphorus and sulphur, too, show reluctance in In ordinary uniting with oxygen, in absence of moisture. It is moist air, carbon monoxide burns with a blue flame. together.
nearly insoluble in and has no action on water.
Other methods of preparing carbon monoxide are by withdrawing the elements of water from formic acid by adding it drop by drop to warm concentrated sulphuric :
O
HC - OH + H SO
= CO + H 2 SO 4 .H 2 O
by heat-
acid
;
ing
a mixture of oxalic acid with concentrated sulphuric
acid
;
2
CO.OH
+
|
H
CO.OH
9
4
SO 4 = CO
+
;
CO 2 + H SO 4 .H O 9
2
;
carbon dioxide is separated from the monoxide by bubbling the mixture of gases through a solution of caustic potash, which absorbs the dioxide, allowing the monoxide the
to pass
;
and
by heating a mixture of potassium
lastly,
may
HCN,
cyanic acid, with water, forming i
+ H 9 O = NH 3
is
first
ferro-
be taken that hydro-
liberated,
and that
it
reacts
HCN
ammonia and carbon monoxide + CO the ammonia subsequently combines :
;
with the sulphuric acid. If carbon monoxide is passed over metallic nickel or iron in a fine state of subdivision produced by reducing their oxides, volatile compounds are formed of the formulas Ni(CO) 4 , and Fe(CO) 5 ; on exposing the latter to light gold-coloured crystals are formed, of the formula Fe 2 (CO) r
The
nickel carbonyl boils at 43, and the iron pentaat 103 di-ferro-hepta-carbonyl decomposes
carbonyl
;
NITROUS OXIDE when even moderately
At
heated.
1
80
95 these
compounds and carbon monoxide, the metal being deposited as a mirror on the hot surface. is most readily prepared by Nitrous oxide, 2 O, are
decomposed
into metal
N
ammonium
heating
NH NO 4
3
NH NO
nitrate,
4
- N,O + 2H 2 O.
water, and
best
is
It
is
3
;
the equation soluble
somewhat
is
:
in
by downward displacement.
collected
The
aqueous solution has a sweetish taste ; and the gas, if breathed, produces insensibility ; it is therefore frequently If a mixture with produces with some persons a state of " excitement, which has procured for it the name laughingIt is an endothermic compound, and if submitted to gas." sudden shock it explodes with violence. It may be supposed that the fulminate used to explode it decomposes some molecules in the neighbourhood ; these, on decompos-
employed by air
is
dentists as an anaesthetic.
respired,
it
ing, evolve heat, and decompose their neighbours, and the explosion rapidly travels throughout the gas ; the products are nitrogen and oxygen. candle will burn in nitrous
A
oxide, for the temperature of the flame is sufficiently high to decompose the gas, and the combustion proceeds as in
Although nitrous oxide is not acted on by oxygen. water or bases it has claims to be regarded as the anhydride of hyponitrous acid, from a solution of which it is liberated
dilute
by heat
nium
:
N-OH N, \O + H O. N-OH N/ li
||
nitrate nor
9
As
neither
ammo-
hyponitrous acid can be reproduced by
bringing together nitrous oxide and water, its production by " irreversible heating one of these compounds is termed an reaction."
Action of Nitric Acid on Metals. The product of the action of nitric acid on metals varies according to the metal acted on, the concentration of the acid, and the temperature.
The
acid in aqueous solution
+
ionised, the ions being
H
and
NO
3
.
is
more or
less
If a metal of which
MODERN CHEMISTRY
96
the ions are highly electropositive is presented to these ions of nitric acid the hydrogen ions impart their charge to the
non-ionised metal, which metal enters into solution as ions, This is the case when nitric while hydrogen is evolved. acid acts on magnesium, and theoretically also on aluminium,
manganese, zinc, cadmium, iron, cobalt, and nickel, for
all
these metals in the ionic state have higher electro-affinity than hydrogen, and that in the order given. It may be
termed the normal action of acids on metals, and repre-
++
M+2H = M-fH
sented thus:
2
.
But along with
this
action others take place in which the nitric ion is " reduced" or deprived of oxygen. Some examples of this will
now
When
NO
9 , is
be given. silver is attacked by nitric acid, nitric peroxide, The reactproduced, and partly evolved as gas.
H substances
ing
NO
are
and
Ag,
N0
+ and
H
3
-
one
;
of the
N0 3
groups loses oxygen, being converted into electrically
3
NO
and an ion of oxygen, O, which combines 2 with the two hydrogen ions, forming water, non-ionised, O. But this leaves a negatively charged nitrate group 2 morewithout a corresponding positively charged partner over, the charge of the decomposed nitrate group is still An atom of silver, therefore, goes into solution available. neutral
H
;
as a positively
charged ion, and restores electric equilibrium
With
in the solution.
less
concentrated acid the nitrate ion
parts with two atoms of oxygen, requiring three negative electrons, in addition to the one originally attached to the
group
NO
3
;
to
effect
this
three positive electrons must which then go
attach themselves to three atoms of silver,
+ into
solution as ions,
hence the charge
+
4NO 3 = NO + 2H 2 O + 3 Ag + 3NO 3
,
is
:
3
Ag + 4H +
the balance of elec-
OXIDES OF NITROGEN
97
trie charge not having been disturbed, although one negative and one positive electron have disappeared. With metals yielding kations of higher potential, the reduction of
the nitrate
ion
goes
nitrogen, and even
farther
still
;
nitrous
N
oxide,
ammonia may be produced,
in
2
O,
relative
amounts depending on the metal, on the concentration, and on the temperature. It may be taken that the lower the temperature, the less the concentration, and the higher the metal stands in the electro-negative series, the greater the reduc-
+
The
tion.
+ 5 H2
+ 4"M + 8N0 3
6H O + 5 M~+ oNO 3 i
"
4M" + ioH + ioNO 3 = N 2 O = N2 + 5 M" + 1 2H + 1 2NO 3
equations are: ;
4 M"
;
3H.7 O.
All
+ oH + oNO 3 = NH 4 + i
these
i
changes
may proceed
simultaneously ; but copper and moderately strong nitric acid yields fairly pure nitric oxide ; if more concentrated acid be employed, a mixture of varying proportions of nitric
while by using zinc or oxide and peroxide are evolved very dilute acid, nitrous oxide, nitrogen, hydrogen, and ammonium nitrate are the main ;
magnesium and products.
Oxidation by means of Nitric Acid. Action of when an element capable of chang-
the same nature occurs ing its
its valency, i.e. the number of electrons associated with ionised atom, is treated in the ionic condition with nitric
For example, the
acid.
ferrous ion,
++ Fe, on treatment
+++ with
oxide
nitric is
acid at
evolved
:
100 ++
3Fe +
becomes + 6R + 4
ferric,
H + 4NO
R
being
Fe, while
nitric
= NO + 2H O 3
any monovalent anion.
Such operations are usually spoken of as "oxidations in the wet way." Nitric oxide is a colourless gas, very sparingly soluble in water on bringing it into contact with oxygen, unless VOL. II. G ;
MODERN CHEMISTRY
98 moisture nitric
is
absolutely excluded, union takes place to form with a trace of nitrous 2 , along 2 3,
peroxide,
NO
NO
On sufficiently cooling nitric oxide it conanhydride. denses to a colourless liquid, and at a still lower temperature it forms a white solid.
Nitrous anhydride, strictly speaking, belongs to the class
N
of acid-forming oxides ; its formula is O g When nitric 2 oxide and nitric peroxide are brought together, only a minute O 3 is formed ; that is, because on converting quantity of 2 .
N
into the gaseous state into these products.
decomposes almost completely cooling such a mixture, however, a blue liquid condenses, which has the formula It 9 g will be afterwards alluded to. it
it
On
NO
.
Nitric peroxide, as usually seen mixed with air at When ordinary temperatures, is an orange-coloured gas. pure it condenses to an orange-red liquid, boiling at 22 ; freezes at -10 to a colourless solid. The liquid has a molecular weight corresponding to the formula and 2 4, the gas, at temperatures not much exceeding the boilingBut as the point, consists mainly of the same substance. it
NO
temperature rises the colour grows darker, until, at 140, it forms a blackish-red gas, consisting wholly of With 2 dissociates in its progressive increase of temperature 2
NO
.
NO
turn into
As
NO
and
temperature
O
falls
2,
and
at
the action
600 is
the change
is
complete.
reversed.
The next class of Neutral Oxides, Class II. oxides comprises those which may be termed neutral, because they can act either as bases or as acids, according Their as they are treated with an acid or with a base. case hydroxides may be comprised in the same class. of this kind has already been explained on p. 70 ; it is
A
there
shown
when treated with with bases aluminates
that aluminium hydroxide,
acids, yields salts of aluminium, while
are formed.
Complexity. It appears probable that such oxides have molecular formulae more complex than those usually ascribed to them; for instance, aluminium oxide is certainly
NEUTRAL OXIDES more complex than
may be A1 4 O 6
is
99
implied by the usual formula
A1 2 O 3
;
no means at present of determining the degree of complexity of the molecule. The argument in favour of this view is the very high It is a melting-points and boiling-points of such oxides. well-known fact that as the molecular weight of compounds it
Al^Og, but there
or
is
increases the this are best
merism
"
is
boiling-point rises. Examples to illustrate drawn from carbon compounds, where " polynot infrequent that is, where compounds exist ;
same percentage composition but molecular formulae, of which the higher ones are multiples of the having
the
We
are acquainted with a series of comlower one. pounds of carbon and hydrogen, of which the first member bodies of the formulae C 4 S , C 6 12 is ethylene, C 2 4 C g 16 , C 1Q 90 , &c., are also known ; and the boiling-point increases with the molecular weight. Now, the chlorides of the elements are, as a rule, easily volatile, and have low melting-points and where it happens that both chloride and oxide have a simple molecular formula, as, for example, carbon tetrachloride, CC1 4 , and carbon dioxide, the , chloride has always a higher boiling-point than the oxide. It would appear to follow, therefore, that if the oxides of the metals had as simple molecular formulas as the chlorides As this they would show more volatility than the latter. is not the case, the presumption is that the oxides possess more complex formulae than we are in the habit of ascribing This probability will be dealt with as occasion to them.
H
H
H
H
H
;
,
;
CO
arises.
Among the oxides and hydroxides which exhibit the power of acting both as acid and basic compounds are cupric hydroxide, Cu(OH) 2 , which dissolves in a concentrated solution of potassium hydroxide with a dark blue colour; zinc and cadmium hydroxides, which dissolve in excess of alkali sodium zincate has been separated by addition of alcohol, and is precipitated in white needles of the formula Na 9 ZnO 9 .8H 9 O; and aluminium hydroxide, which dissolves in alkali, forming an aluminate, MA1O 2 ; ;
MODERN CHEMISTRY
ioo
and
stannous
Pb(OH) 2
plumbous hydroxides, Sn(OH) 2
dissolve
,
in
alkalies,
forming
and
compounds no
doubt analogous to zincates. Chromous, ferrous, manganous, cobaltous, and nickelous hydroxides are not thus soluble.
Chromic hydroxide, however, is soluble in soda, probably unlike the forming a compound like sodium aluminate latter, chromium hydroxide is thrown down on boiling the ;
solution.
But such compounds, when they do not contain sodium or potassium, are often insoluble in water, and then they cannot be prepared by the action of the one hydroxide on
The oxides combine when heated together in dry condition, and sometimes when the compound formed is decomposed by water (hydrolysed) it is convenient to prepare it either from the oxide or from the the other.
the
carbonate.
A
Spinels.
considerable
number
of
compounds,
analogous to the aluminates, is produced in this way, and many of them are found in nature as minerals. To this
" belong the spinels," so called because one of their native the aluminate of magnesium, had received number, Viewed as a combination of oxides, such comthis name. and they pounds possess the general formula 2 3 .MO, can be prepared by heating the sesquioxide (a name given to oxides when the proportion between the metal and the class
M
O
oxygen is as one to one and a half, or, more correctly, as two to three) with the monoxide. The spinels all crystalin regular octahedra ; they are therefore said to Viewed as aluminates, be isomorphous with each other. compare NaAlO 2 . they may be written 2)2 ; Among them are true spinel, Mg(AlO 2 ) 2 ; franklinite, lise
M"(MO
Zn(FeO 2 ) 2 or
;
Be(AlO 2 ) 2 and But it is Fe(CrO 2 ) 2
chrysoberyl,
"chrome-iron ore,"
;
.
chromite, not neces-
ones ; sary that the metals of a spinel should be different if a metal is capable of existing in two forms, e.g. as dyad Such are and triad, it may form a similar compound.
magnetite, or "magnetic iron ore," Fe"(Fe'"O 2 )
,
and
SPINELS hausmanite, Mn"(Mn'"O 9 ) 2 like
manganese being dyad, triad, like
101
the first atom of iron or magnesium, and the second ,
aluminium.
Reasoning by analogy,
it
would appear not unlikely
that
native oxides, such as alumina (corundum, ruby, sapphire), or iron sesquioxide (haematite), may be in reality an
of
aluminate
A1(A1O
alumina,
) 3,
or
ferric
ferrite,
Fe(Fe0 2 ) r
A
common
for
test
and aluminium
zinc
to
is
heat
together before the blow-pipe the salt suspected to contain the metal with cobalt nitrate ; it is probable that the green colour produced by zinc is due to the formation of a cobalt
Co(ZnO 2 ), and the blue colour shown by body, Co(AlO 2 ) 2 When lead is heated to redness in air the first of its oxidation is litharge, PbO on continuing zincate, to a similar
alumina
.
product
the application of heat, at a carefully regulated temperature, the yellow litharge becomes red, and the product of the action ;
is
minium
lead lead
Red
"red lead," Pb 3 O 4
. Now, on treating red acid, lead nitrate dissolves, while dioxide, hydrated, remains as an insoluble residue. lead, therefore, may be regarded as a compound
or
with dilute
nitric
between two molecules of monoxide and one of dioxide, 2 PbO + PbO the former reacts with nitric acid forming 2 the nitrate, while the latter remains. Now, if the dioxide be heated with caustic potash it dissolves, forming potassium and red lead may be regarded as a plumbate, K.,PbO 3 ;
;
O//Pb\VPbO IV
basic
plumbous plumbate,
" 3)
;
basic,"
\pb"/ because the partly salt is
;
first written atoms of lead are partly oxide, they are dyad, while the second atom of lead
tetrad. It
is
position
view.
to regard of nitrosyl,
possible
as a nitrate
nitric
peroxide
O=N NO 3
in
this
light
easy decommilitates against the
;
but
its
into NO when heated Compounds of antimony and bismuth, having
the
MODERN CHEMISTRY
102
Sb 2 O 4 and Bi 9 O 4
formulae as
and
O=Sb(SbO 3 )
there
may be
,
O=Bi(BiO 3 )
no proof.
is
Manganese and chromium
attributed
O, and
too,
they,
;
similarly
of
this,
regarded however,
form " dioxides," to and CrO 2 are usually
also
MnO 2
which the simple formulas
;
may be
o
written
><X
VI
They would
VMn< xx;>Mn". cr
then be termed
chromous chromate and manganous manganate. Such ideas must be regarded as speculative, but there can be little doubt that the formulae are more complex than they are
The former is a snuff-coloured powder, produced by the action of nitric oxide on a chromate ; the latter, formed by oxidising and precipitating a manganous usually written.
salt simultaneously, is best prepared in a hydrated state by the action of a hypobromite on a manganous salt: MnCL.Aq
^NaOBr.Aq + 2NaOH.Aq = O=Mn(OH) 2 + NaBr.Aq
+ aNaCl.Aq.
It
and
is
a
common
known
black mineral in the anhy-
It will be repyrolusite. membered that the ordinary method of preparing chlorine is to heat this mineral with dilute hydrochloric acid, and also that on heating alone it furnishes oxygen, being itself converted into Mn 3 4 , a brown powder, which may be formu-
drous
state,
is
as
O
lated as a spinel, viz.
(O=Mn O) 2 =Mn.
In concluding this chapter on neutral oxides, it may be mentioned that there are a few which, acting generally as feeble
bases, yet
display
feebly
acid properties
if in
the
Such are presence of a strong base like soda or potash. the oxides of gold, the metals of the platinum group, and of titanium, zirconium, and thorium. of these elements are soluble and nitrates of the last three.
num, however,
are hydrolysed
sulphuric acid, thus
:
Pt(SO 4
)
2
The
chlorides
in water, as also the sulphates
Sulphates of gold and platiby water, giving oxides and
+
2HOH - PtO
2
+ 2H 2 SO 4
.
NEUTRAL OXIDES
103
Salts of these elements, on treatment with soda, yield no precipitate, for they are dissolved by the alkali ; the compounds
formed are
indefinite,
MAuO
but
it
may
be supposed that they
.Aq, or platinate, titanate, zirconate, MPtO 3 .Aq, &c. Iron and calcium titanates FeTiO 3 is termed ilmenite, and CaTiO 3 occur native The first is isomorphous with and crystalperowskite. contain aurate, or thorate, ;
lises
"
the ore is known as along with native ferric oxide iron ore." It is the commonest compound of
titanic
titanium.
;
CHAPTER
VI
Acids and Salts Basic and Chlorides The Borates The Carbonates Thiocarbonates Other Acids containing bon; their Salts with Alcohol Radicals Silicic Acids and the Silicates.
Anhydrides
Basic Salts.
Many compounds
are
Acid
and Car-
The
known which
are
the same time chloride and oxide, or chloride and hydroxide of elements. Where the element with which the at
oxygen and chlorine is combined oxide, the compounds in question
is
one which forms a basic
are termed basic chlorides.
Similarly, there are basic bromides and iodides.
For ex-
ample, zinc oxide heated with zinc chloride forms oxychlorides, of which the simplest example is Cl~Zn~O~Zn~Cl; aluminium chloride, evaporated with water, has its chlorine gradually replaced
C1 2 -A1(OH),
though
at a
by hydroxyl, forming successively and finally, A1(OH) 3 , ,
C1-A1=(OH) 2
temperature sufficient to complete the reaction, would probably form the condensed hydr-
the aluminium
We
O=A1OH
instead of the trihydroxide. shall other groups, playing a part analogous to that of the chlorine in a basic salt, may also exist in basic
oxide
see later that
salts.
Acid Chlorides. chlorides
exists,
Another class of double oxides and most of which are easily volatile, and
These which therefore are of known molecular weight. " acid chlorides" oxychlorides of those elements which form acids. These are related to acids, in are the so-called
as
much
as
by replacement of 104
their chlorine
by hydroxyl,
BORATES acids are formed.
It will therefore
them along with the acids
sider
A general
to
105
be convenient to con-
which they
are related.
idea has already been given of the nature of acids in describing the hydroxides of zinc and of aluminium. As a rule, acids are condensed hydroxides ; that is,
hydroxides which, having lost the elements of water, are oxides, partly hydroxides. They also possess the into one more of or ionising hydrogen ions and an property In following the order electro-negatively charged radical. of the periodic table, after such feebly acidic hydroxides as those of zinc and aluminium, hydroxide of boron claims partly
attention.
Borates. In when evaporated,
Na^Of. ioH 2 O
white, crystalline soluble in cold.
;
lakes in
certain
California the water,
of the crystals deposits this substance is named borax.
formula It
is
a
soluble in hot water, but sparingly mixed with sulphuric acid nacreous
salt, easily
When
of the formula B(OH) 3 , or, as it is usual in writing the formulae of acids to place the hydrogen atoms Boracic acid hardly deserves the name of first, 3 3 acid in aqueous solution it exists almost entirely in the non-ionised state. No ions are volatile ; but this compound issues in Tuscany and in the Lipari Islands along with steam from cavities in the ground, termed suffioni ; it is scales separate
H BO
.
;
easily recognised, for
held in the steam.
water and a
is
vitreous
BaOoi
is
imparts a green colour to a flame heated to 100 boracic acid loses
into
changed
substance
left
stitution is
it
When ;
metaboracic acid, O=B- OH, at a red-heat boron oxide,
and
as a transparent,
colourless glass.
Its
con-
O=B-O-B=O.
The borates
of the alkalies are prepared by mixing with the hydroxide of the alkali metal ; although there are very few hydrogen ions in an aqueous solution of boracic acid, however dilute, yet some of those present combine with the hydroxyl ions of the alkali, forming boracic
acid
water, thus:
H BO 3
3
.Aq + sNaOH.Aq = Na 3 BO 3 .Aq +
MODERN CHEMISTRY
io6
O. But there are so few ions present, that those of 2 the water, which, it will be remembered, is ionised, although to an extremely minute extent, are yet sufficiently numerous
3H
some proportion to those of the boracic acid ; hence the reaction given above is perceptibly reversed, and on " dissolving borax in water it is hydrolysed," that is, split the and by hydrogen hydroxyl ions of the water into nonionised boracic acid and caustic soda, the latter, of course, to bear
largely ionised as usual.
It
is
therefore possible to estimate
the sodium of borax by addition of a solution of a strong acid, such as hydrochloric or sulphuric acid of known con-
no boracic acid were present, provided used as an indicator. (See p. 75.) Thus the addition of 36.5 grams (H=i; 1 = 35.5) of hydrochloric acid, dissolved in a litre of water (such a solution is termed a "normal solution"), to 191 grams of centration, just as if
methyl-orange
be
a solution of crystallised borax in
a litre of water
[Na 2 = 4 6 + B 4 = 44 + O 7 = ii2 + ioH 2 O = 180])
(1/2 ;
(in
1/2 of 382) gives a solution which is neutral to methylorange. Fused borax has the property of dissolving oxides of the metals, forming complex borates ; certain of these are coloured, and their formation is often made use of for all
detecting the presence of such silver
metals as copper (blue), (yellow), chromium (green), ferric iron (yellow),
ferrous
heated
iron in
a
(bottle-green), manganese (amethyst, when flame containing excess of oxygen), cobalt Borax is also used for nickel (reddish).
(blue), and soldering easily oxidisable metals, such as iron, copper, or brass ; the film of oxide which prevents the metal touching
Both borax and alloying with the solder is thus removed. and boracic acid have considerable antiseptic properties, and are used for preserving eggs, milk, and other animal and vegetable substances.
Carbonates and
Thiocarbonates.
bonates and the thio carbonates dioxide
(or
rather
The
car-
are derivatives of carbon
of carbon oxy-hydroxide,
commonly
CARBONATES
107
and of carbon disulphide. Carbon is a and the analogue of carbon tetrachloride would be the tetrahydroxide, C(OH) 4 ; but this body is unstable, and called carbonic acid),
tetrad,
its first
anhydride,
O=C(OH)
However, carbonyl
solution.
2,
is
known
chloride,
only in aqueous
O=CC1
,
exists
;
produced by the direct union of carbonic oxide with chlorine, when a mixture of both gases is exposed to it was formerly known as " phosgene gas," sunlight it
is
;
"made by light"; but it is more conveniently prepared by passing a mixture of the two gases over animal charcoal heated to redness. It condenses to a meaning
It liquid, boiling at 8.4. water, thus: O=CC1 2 +
is
immediately decomposed by
2HOH = O=C(OH)
if sufficient
water
in solution.
The
2
+ zHCl;
present, the carbonic acid can remain existence of the oxychloride establishes is
the formula of carbonic acid.
Carbonic acid
decomposable substance ; of water be present, it splits into its anhydride, CO 2 , and water: O=C(OH) 2 = 2 O. The anhydride is a colourless gas, which con-f denses to a solid at about 80 ; it can be liquefied only under pressure. Carbon dioxide, or carbonic anhydride, is
a very easily
if liberated, unless a great deal
CO
H
produced by heating a carbonate as already remarked, carbonates, except those of the alkaline metals, are decomposed by heat, forming oxides, and evolving carbon dioxide. It is also produced when carbon or carbon monoxide is burned with excess of oxygen. Lastly, it is produced in large quantities during the process of fermentais
;
all
Glucose, or grape sugar, either produced
tion.
by the
hydrolysis of starch or extracted from fruits like grapes, when mixed in dilute aqueous solution with yeast, a vegetable
organism, decomposes into ethyl alcohol and carbon dioxide, thus: C 6 12 6 + 2CO 2 The carbon di2 5
H O =2C H OH
oxide being heavier than tuns
;
it
is
liquefies ; like solid,
now
often
air,
.
collects
collected
in
the
fermenting
and compressed
until
it
and the liquid on expansion solidifies to a snowused for producing low temperatures.
MODERN CHEMISTRY
io8
A
of carbonic
solution
carbonic
owing
acid,
O=C(OH)
to the small extent of
in
anhydride
which
,
its
a
is
ionisation.
water contains very weak acid It
is
probable,
too, that liquid carbon dioxide exists in the solution, mixed, but not combined with the water. Carbonic acid reacts
with sodium, potassium, calcium, or barium hydroxide, - -
f
forming carbonate of the metal
:
H CO 2
+
3
.
-
Aq + zNaOH. Aq
2H
CaCO
O. In such actions it is only the ionised 3 + portion of the acid which reacts, and the hydrogen ions form water ; when these are removed another portion becomes ionised
in order to restore equilibrium ; it reacts in has become transformed. On evaporation of the solution the alkaline carbonate is left as a white crystalits
turn until
all
sodium carbonate, Na CO 3 ioH 2 O, All other carbonates are insolconsequently thrown down as precipitates on adding a solution of sodium carbonate to any ionised solution of other metals. They form flocculent precipitates, generally possessing the colour of the ion of the metal; thus copper carbonate is blue, ferrous But with the exception of green, cobalt pink, and so on. the carbonates of the metals of the sodium and calcium all other carbonates are " that line
salt;
hydrated
.
is
ordinary washing-soda. uble in water, and are
basic/' groups precipitated they are partly hydroxides, partly carbonates. Copper carbonate, for example, may be assigned the formula
is,
/O-Cu-OH
O=C\ \O-Cu-OH of copper
is
;
it
will
be noticed that each atom
combined with the oxygen of the carbonic
residue on the one hand, and with hydroxyl on the other. The paint known as " white lead " consists of a basic
carbonate of lead, more complex than the example given above, of the formula
HO-Pb-O-(CO)-O-Pb-O-(CO)-O-Pb-OH. Native Carbonates.
Many
carbonates exist in the
ACID CARBONATES
109
some are widely distributed minerals. Among these are Iceland or calc-spar, arragonite, limestone, chalk, and marble, all of them calcium carbonate; native state
;
strontianite,
FeCO 3
ore,
with
clay,
,
SrCO 3
;
witherite,
BaCCX
spathic iron
;
named clay-band when contaminated black-band when mixed with shale.
also
and
MgCO 3 ; dolomite, a mixture of magneand and calcium carbonates; calamine, ZnCO 3 Malachite and azurite are basic carcerussite, PbCO 3 Magnesite
is
'sium
;
.
/O-Cu-OH
bonates of copper,
O
O=C\
X 0-Cu-OH O
and
,
HO-Cu-O-C-O-Cu-O-C-O-Cu-OH.
We
see here again that with weak bases, such as the hydroxides of most metals, the carbonates tend to become This is why the precibasic, that is, to be hydrolysed. pitates obtained on adding a soluble carbonate to a salt of such metals are basic, and not normal carbonates.
"Acid" Carbonates. "
The name "acid carbon-
given to a double carbonate of hydrogen and a metal. Such bodies are prepared by the method which always is adopted for the preparation of double salts by
ate
is
/ONa mixture.
Hydrogen sodium carbonate,
O=C\X OH
the corresponding
potassium compound
cium carbonate
HO-C-O-Ca-O-C-OH,
O
O
I!
li
;
;
hydrogen cal-
a ferrous
carbonate of similar formula, and many others are all formed when carbonic acid and the respective normal carbonate are mixed, the mixture being kept cold. On raising the temperature of all of these, carbon dioxide escapes, and " Acid " carbonate the neutral carbonate is again formed. " " of sodium is the common baking-soda ; hydrogen calcium
MODERN CHEMISTRY
no
of many natural waters, and is the " termed " temporary hardness ; for on boiling the water the neutral carbonate is precipitated, and the water ceases to be '* hard." The same result may be carbonate
is
a constituent
what
cause of
is
effected, paradoxical as it may appear, by the addition of lime-water ; for then sufficient calcium hydroxide is present to form normal calcium carbonate with the hydrogen carbonate, thus
:
2H 2 O.Aq.
Ca(HC0 3 2 .Aq + Ca(OH) 2 .Aq - 2CaCO 3 + )
ferrous carbonate
Hydrogen
is
a constituent
on exposure to the atmosphere the iron is oxidised to ferric hydroxide, and the carbonic acid, being too weak an acid to form a carbonate with such a of chalybeate springs
weak
;
base as that, escapes:
2Fe(HCO 3 2 .Aq+ 5H 2 O +
O = 2Fe(OH) + 4 H CO 3 .Aq. 3
2
)
The
ferric
hydroxide
is
deposited as a brown scum on the banks of the streams flowing from such wells.
Carbonates of Radicals.
Although normal hydrunknown, yet if the hydrogen be replaced The compound, by ethyl, -C 2 5 the compound is stable. which is produced by the action of carbon tetrachloride on sodium ethoxide, CC1 4 + 4 Na-O-C 2 5 = 4 NaCl + oxide of carbon
H
is ,
H
C(O-C 2 HJ 4
of C(OH) 4 It is a And volatile liquid, and is named ethyl orthocarbonate. the a corresponding carbonate of ethyl, O=C(OC 2 5)2 analogue of carbonic acid, O=C(OH) 2 , is formed by treating ,
is
the
analogue
.
H
carbonyl chloride with alcohol:
O=C(OC 2 H
5)2
+ 2HC1.
and can be weighed
in
,
O=CC1 2 + 2HO-C,H 5 =
These compounds
are volatile,
the state of vapour, hence their known, and this is an additional
molecular weights are proof of the correctness of the formulae ascribed to carbonic acid and the carbonates.
Thiocarbonates. The sulphocarbonates, or (from the Greek theion, sulphur) form
bonates
thiocara
class
analogous to the carbonates, both in their formula? and in the method of their preparation. Carbon disulphide,
of
salts
a volatile liquid, boiling at 46, possessing a disagreeable smell, is produced when sulphur vapour is led over charcoal
THIOCARBONATES
in
in fact, the carbon is heated to redness in a fireclay tube When shaken with a concentrated burned in sulphur gas. aqueous solution of the sulphide of sodium or potassium, it Na 2 CS 3 or dissolves, forming the compound 9 CS 3 . ;
K
,
These
thiocarbonates, like the carbonates, are white, crystal-
on adding acid, thiocarbonic acid separates as slowly decomposes, especially if warmed, into hydrogen sulphide and carbon disulphide. Many of its salts are insoluble, and may be prepared by precipitation. The formula of carbon dioxide is CO 2 that of carbon and it is evident that an intermediate disulphide CS Q substance should exist of the formula COS. This subline salts
an
oil
;
it
;
,
;
stance
is
carbon oxysulphide.
It
a gas, prepared by
is
ammonium salt of produced when ammonia is passed through a mixture of carbon disulphide and alcohol CS 2 + 2NH 3 .Alc - 2 S + (NH 4 )SCN.Alc. On evaporation of the alcohol the ammonium thiocyanate crystallises out. This salt, disheating thiocyanic
which
acid,
HSCN,
the
is
:
H
with sulphuric acid, yields in passing the acid HSCN, which, on account of the high temperature, reacts with
tilled
water, forming ammonia (which yields ammonium sulphate with the sulphuric acid) and carbon oxysulphide, :
COS
HSCN + H O = NH 3 + COS. 2
Like nitrous oxide, carbon disulphide is an endothermic compound, and can consequently be decomposed by shock ; when a fulminate is exploded in it, it is resolved into carbon and sulphur. On the other hand, carbon dioxide and oxysulphide are exothermic during their formation.
compounds, heat being evolved
Acids containing Carbon.
An
enormous number
of acids containing carbon is known, in which the acidic carbon atom is combined with oxygen and hydroxyl, and also with hydrocarbon residues, such as methyl or ethyl, or with
some more complex group of carbon atoms.
The
o
simplest
I!
of these
is
formic
acid,
H-C OH.
Acetic
acid
is
MODERN CHEMISTRY
H2
O methyl-formic acid
OH
(CH 3 )-C
ethyl-formic acid
;
is
O 11
named
propionic acid
Oxalic acid the
;
formula
its
is
CH CH C OH. O=C-OH g
2
to be regarded as di-carboxyl,
is
name carboxyl being
a contracted
,
I
O=C-OH
form of" carb(onyl
hydr)oxyl" ; it is commonly written CO OH. Formic acid (from formica, an ant) is contained in ants and stinging nettles. Sodium formate is produced when carbon monoxide is left in contact with sodium hydroxide ;
the reaction takes a considerable time
:
H CO ONa. It in presence H CO OH. It
is also formed by heating oxalic acid, of glycerine: (CO OH) 2 = CO + is a colourless, pungently smelling liquid, and a fairly strong acid in aqueous solution ;
better
boiling at
CO + NaOH =
99,
Its salts are crystalline, and possess the poisonous. colours of the metallic ions which they contain. When it
is
warmed with concentrated
sulphuric acid, or with other substances capable of withdrawing water, it yields carbon is not the true Yet monoxide. anhydride of formic
CO
acid, seeing that an anhydride can be obtained only
from
of the elements of water from hydroxyl groups, for the real anhydride formic acid contains the group ; loss
H C=
O
O II
II
H
C would be Acetic acid solid,
O C
H
;
it is
unknown.
the acid constituent of vinegar, and
is
is
a
It can to a liquid, boiling at 118. carbon contact into bringing by synthetically
melting at 17
be formed dioxide and sodium methide, a compound of the formula
Na-CH,; the H 3 C CO ONa
;
equation the sodium
acid, yields acetic acid.
the distillation of
wood
is
:
Na-CH 3 + CO = 2
with sulphuric It is produced on a large scale by the distillate consists mainly of ; salt, distilled
"ORGANIC ACIDS" acetic acid
and
and methyl alcohol
when
the alcohol passes over, leaving behind acetate ; this is evaporated to dryness, and
distilled,
the calcium heated, so
wood
as to
distilled
is
;
113
neutralised with lime,
is
it
;
char tarry matters, also produced when the calcium salt is finally distilled with
Acetic acid is also formed by the of aldehyde (p. 88), which is itself an oxiThe connection between dation-product of alcohol. acid.
sulphuric
oxidation
these
bodies
is:
CH -CH -OH, CH 9
3
O
8
--CH=O,
and
as
the
I!
CH -C-OH. 3
of
anhydride
CH
= C(OH) 3
3
Aldehyde 3
.
The
be
may
CH -CH=(OH)
regarded
and
,
acetic
acid
of
;2
usual oxidising agent
is
chromic
if the acid product of oxidation is conveyed away as it is formed by sloping the condenser downwards, aldehyde is if the aldehyde is returned to the oxidising obtained mixture by sloping the condenser upwards, and cooling with ice and water, the product is acetic acid. The oxidation is " also effected by an organism called " mother of vinegar ; sour wine or beer is allowed to trickle down a cask filled with shavings of beech-wood, on which the slimy masses of the organism are growing oxygen enters, and the vinegar flows out at the bottom of the cask. ;
;
;
On
distilling acetic acid
hydroxyl PCL = 4
is
exchanged
with phosphorus pentachloride,
for chlorine
CH -CO-C1 + H P0 3
3
4
is named acetyl chloride regarded as hydroxide of the group on treating acetyl chloride with water
obtained
CH -COC1 + H- OH 3
=
4CIrL
:
+ HC1. ;
CO OH +
the compound
acetic
acid
may
it is
at
CH -CO-OH 3
be
and once formed
(CH 3 C=O)
,
:
+ HC1.
And
aldehyde may be regarded as a hydride of acetyl, similar body cannot be made from formic acid, for it decomposes into carbon monoxide and hydrogen chloride H-CO-C1 + HC1.
(CH 3 CO) H.
A
:
Oxalic acid
CO
contained as hydrogen-potassium salt in the plants sorrel and rumex. It can be prepared by the is
MODERN CHEMISTRY
ii4
oxidation of sugar with concentrated nitric acid, or by heating sawdust with a mixture of caustic soda and potash in shallow trays ; on treating the charred residue with water, sodium oxalate, a comparatively insoluble salt, remains, while the excess of alkali dissolves ; the sodium oxalate is
extracted with boiling water, and calcium chloride is the almost insoluble calcium this ; precipitates
added
oxalate ; and on digesting it with the equivalent amount of sulphuric acid, sparingly soluble calcium sulphate remains,
while oxalic acid dissolves.
The
filtered
solution,
when
C(OH) 3 evaporated, deposits crystals of ortho- oxalic acid,
C(OH) 3
CO-OH which,
at
100, dehydrate
to
.
Oxalic acid
is
|
CO-OH
and its salts, like those of formic and acetic have the colour of the positive ion. It cannot be for the anhydride, which should possess further, dehydrated a di-basic acid,
acids,
CO the formula
P>O,
CO
decomposes
into
CO
and
CO 2
.
Salts of these acids with alcohol radicals, such as methyl and ethyl, are prepared by saturating a solution of the acid in the respective alcohol with hydrogen chloride, = (COOCH 3 ) 9 and then distilling: (COOH) 2 + 2 3 + 2HOH. The hydrogen chloride serves to withdraw Such salts 3 water, and prevent it acting on the product.
CH OH
which are generally colourless liquids or solids, possessing a pleasant smell, are called " esters." a rule they are sparingly soluble in water, and are not ionised in solution,
As
When boiled with thus differing from salts of the metals. alkalies, the ester being returned by means of an inverted condenser into the boiling-flask, they change into alkalies, and the alcohol:
salts
of the
CH,-CO-O-CH -CH + KOH.Aq = CH -CO-OK.Aq + CH -CH -OH. 3
This change
is
also effected by
3
8
2
2
heating with water in a
SILICIC ACIDS
115
accelerated by the presence of hydrogen ions, and therefore by the presence of strong acids, such as sealed tube
;
it is
of Decomposition "
hydrochloric acid.
"
"
called
is
saponification
"
is
hydrolysis
;
applied to
kind by alkalies by water the term
this
if effected
it.
Acids and Silicates.
While the characterof carbon is to form compounds in which many atoms of carbon are linked together (hydrocarbons, for example, Silicic
istic
having formula like
H H H H-C-C-CH H H
H H
...
-C-C-H),
H H
atoms of silicon are characterised by linking by means of atoms of oxygen. This peculiarity leads to the existence of a large number of silicates, and probably, too, of a The existence of some of large number of silicic acids. these is rendered certain by a study of the oxychlorides. Silicon tetrachloride, SiCl 4 when passed over fragments of felspar (a silicate of aluminium and calcium) heated to ,
whiteness in a porcelain tube, exchanges chlorine for oxygen, at about 137, of the formula
and yields a liquid boiling
O/
This
.
liquid, passed along
with oxygen through
\SiCl 8 a hot glass tube, gave two other liquids, which could be separated by fractionation ; the one, boiling at 153, had the formula Si 4 H Cl 10 , and the other, boiling at 200,
O
Si
4
O 4 Cl s
The
.
vapour-densities
of these
liquids
determined, and led to the formulas given above. signification of this will appear presently.
Si(OH) 4
.
When
silica,
in
the form of
flint,
were
The or fine
sand, or powdered rock-crystal is either fused with caustic soda or potash, or heated under pressure with a solution of one or other of the alkalies, an orthosilicate is pro-
duced, possessing
These
the
formula
Si(ONa) 4
or
Si(OK) 4
.
are soluble in water, and as they resemble " soluble glass in appearance, they are usually named glass." If hydrochloric acid is added to the solution of one of silicates
ii6
MODERN CHEMISTRY
in reality, orthosilicic them, no apparent change occurs acid is produced, a compound which is hardly ionised at all, being one of the very weakest of acids. Osmosis. To separate the ions of sodium chloride and of hydrochloric acid advantage is taken of a discovery made by Graham, that a vegetable or animal membrane like ;
parchment or parchmentised paper
is
readily permeated by
crystalline bodies, while it is very slowly " colloidal " or gum-like compounds. By
permeated by placing
in
a
drum, floating on water, the mixture of orthosilicic acid and salt, the sodium and chlorine ions pass through, of course in equivalent proportions, leaving the colloid behind. Fresh water is substituted from time to time, until all The chlorine ions have been removed from the silicic acid.
water can be removed by evaporation in vacua, and a clear but very viscous liquid remains, which is believed to conOn raising the temperature of this tain Si(OH) 4 .Aq. viscous liquid it gelatinises, and is then insoluble in water ; the resulting compound may have a formula analogous to carbonic acid, O=Si(OH) 2 ; it is termed metasilicic On further drying, water is gradually expelled, and acid. finally a flint-like mass is left, which on ignition yields As already mentioned, a white powder of SiO 2 , or silica. silica is found in nature ; when pure, it crystallises in hexagonal prisms, and is termed quartz, rock-crystal, or It is used for spectacle lenses and optical Irish diamond. instruments.
The
major part of the rocks which constitute the of the earth consists of mixtures of silicates. Occasionally they are found in definite crystals, and on
surface
From their analysis their formulae can be determined. formulas, the formulae of the silicic acids from which they may be supposed to be derived can be deduced ; tables follow, in which the formulas of these silicic acids and of some of the minerals constituting their salts
and
are given.
SILICATES
OH OH OH
117
O O
Be
Si
0\ Be Beryl.
>(Mg,Fe)
,Si0 4 =Al
Fe)
Al~Si0 4 ziAl SiO 4 -Al
>(Mg, Olivine.
Xenolite.
These
Orthosilicates.
comma between
Mg
the
are
and the
orthosilicates
Fe means
the
;
that
these
metals can replace each other in any proportions. Xenolite, it will be observed, is the silicate of a triad metal, aluminium ; and four atoms of aluminium replace twelve molecules of But hydrogen in three molecules of orthosilicic acid.
double
silicates are
hydrogen
in
replaced by three monad atom ; or
- A1=O, or,
lastly,
common,
in
which three of the atoms of
three molecules of orthosilicic acid
monad atoms
may
be
or by one dyad and one have a monad group, such as ;
we may - A1F replacing each atom of hydrogen 2 the aluminium may be partly hydroxide, thus
or
,
constituting a basic silicate.
Si04
=KH
;
Examples of such compounds
4
Al~SiO 4 _CaH Muscovite, or Potash mica.
Prehnite.
MODERN CHEMISTRY
u8
Si0 4 =(AlF 2 ) 8
Si0 4 r(AUO) 3
SiO 4 -Al
Al
SiO 4 =Al
Al
Fibrolite.
Topaz.
OH Al-SiO 4 =H, Kaolin or China-clay. In such
the aluminium
silicates,
metals, such
triad
by
as
triad
often partially replaced iron, or man-
is
chromium,
ganese. Metasilicates
Metasilicates. acid
H
like
that
are
2
SiO 3
are
derivatives
the constitutional formula
;
of carbonic
acid.
Ca
O = Si
is
of the
O=Si(OH) 2
Examples of
,
metasilicates
:
(Mg, Fe", Mn", Ca)
No/ Augite or Hornblende.
Wollastonite.
o
/ \Al - O \0/
O = Si
o II
Si
-
ONa
Jade.
The
potassium
salt is
Leucite.
The molecules of ojthosilicic acid may Disilicates. one molecule of water, the remaining atom of oxygen of the two hydroxl groups serving to unite the two molecules
lose
SILICATES together, thus :
and
a similar loss of water
119
may
be repeated twice,
Si
Si
Disilicic acid.
ist
anhydride.
OH SiO
SiO,
H 2nd anhydride.
The
final loss
acids are not
of water yields anhydrous
known
regarded as their disilicate, thus
Silica.
as such
salts.
CaH 4 Si 2 O 7
It ;
silica.
but certain minerals
;
is
These
may be
probable that okenite
and also
O
is
a
petalite, a derivative
of its second anhydride, AlLi(Si 2 5 ) 2 Similarly, three molecules of orthosilicic acid, by losing two molecules of .
water, may unite to form trisilicic acid ; and it again by successive loss of one, two, and three molecules of water may yield a first, a second, and a third anhydride. The
MODERN CHEMISTRY
120
well-known
and orthoclase are
felspars albite
third anhydride of trisilicic acid, thus
salts
of the
:
O
O
O / \ Al-O-Si -O-Si-O-Si- ONa n
"I
7 N)"
Albite.
/ /~O
Al
ii
-
~.Si
II
O - Si - O
-
Si
OK
-
^cr Orthoclase.
The method of ascertaining the formula of a silicate In order to determine the relative number requires notice. of molecules of silica, SiO , and of the oxides of the various 2 metals in combination with
it,
each percentage
is
divided
the by the molecular weight of the oxide in question quotients are then divided by the smallest, and the ratio between the resulting quotients compared. To take an ;
instance
An
:
analysis of a specimen of muscovite gave the follow-
ing numbers
:
SiO 2 =45.07
H O = 4.42; 9
=
Al 2 O 3 =
K
O = 12.10; 38.4i 2 Dividing by 60.4; by 18.0, the quotients 0.746, 0.375,
per cent.;
together
i
;
oo.oo.
by 102.3 by 94.3 0.128, 0.245 are obtained. Again dividing the quotients by 0.128, the smallest of these quotients, the ratios are: Therefore the formula is 6SiO 2 , 6, 3, i, 2, nearly. ;
3A1 2 O 3
,
K 2 O,
;
2H.2 O,
or,
adding the various constituents
O
The group together and dividing by 2, Si 3 12 AlgKH Si is 3 x SiO 4 ; the compound is, therefore, an ortho3 12 .
O
silicate
;
and three atoms of
triad aluminium,
one of monad
potassium, and two of monad hydrogen are equivalent to the twelve atoms of hydrogen of the three molecules of orthosilicic acid.
It
sometimes happens, however, that one
SILICATES
121
metal, such as magnesium, may replace more or less of In that case, the another, such as calcium and iron.
quotients obtained cular weights are
The pure
;
on dividing the percentages by the moleadded before the final ratio is obtained.
products of Nature's laboratory are seldom, if ever, and it rarely happens that a natural mineral gives
results so easily interpreted as the case given above. the mineral no doubt separates from a matrix in
many compounds are present; and so metal may take the place of another
it
For which
happens that one
possessing the same valency, and capable of forming compounds of the same The alkali metals are mutually replacecrystalline form.
There also the triads Al, Fe, Mn, Cr, and others. even instances where silicon is partially replaced by titanium hence the interpretation of the results of analyses The work of presents a problem of no small difficulty. F. W. Clarke, of the U.S. Geological Survey, has contributed not a little to a solution of this problem. able
;
are
;
CHAPTER
VII
ANHYDRIDES, ACIDS, AND SALTS Phosphoric, Vanadic, Arsenic, and Antimonic Acids Nitrous, Phosphorous, Arsenious Acids Phos-
Hyponitrous and Hypophosphorous
phatic Acid Acids,
and their
Salts.
THE
remaining hydroxides, which all exhibit well-marked may be divided into two classes, those of elements of odd valency, and those derived from elements scheme has already been given on of even valency. illustrates the derivation of the acids of the p. 71, which acid functions,
A
halogens from the imaginary hydroxides corresponding to 111 vn v and stands for halogen, and , , where , , the Roman numerals for the valencies in the compounds.
X
X X
X
X
1
Elements of Odd Valency. The highest valency shown by elements of the nitrogen group, apart from a This is somewhat questionable pernitric acid, is five.
by the formulas of the pentoxides, N O 5 PoO 5 , O 5 , and V 2 O 5 But these compounds possess very different stability, and the elements show different behaviour in uniting with oxygen. Nitrogen and oxygen do not unite except when electric sparks are passed through a mixture of the two gases, or when a high-tension current is It is doubtful whether heat alone passed through air. it is more is the cause of this union probable that energy must be imparted to the combining gases in an electrical The act of combination, in which the product is form. illustrated
,
As 9 O 5 Sb
.
,
;
the peroxide
NO
,
is
attended by absorption of heat
(7700
PHOSPHORIC ACIDS
123
of 14 grams of nitrogen with 32 grams and this energy must be supplied if union is of oxygen) On the other hand, phosphorus burns to take place. in air, and if excess of oxygen be present, the brilliantly calories for the union ;
so-called pentoxide
is
produced
density, however, the formula
is
;
according to the vapourIf air be slowly . 1()
P4 O
passed over heated phosphorus, on the other hand, the are formed. It is not poslower oxides P 4 G and P 4
O
O
sible to
dehydrate phosphoric acid,
P O5
as to obtain
oxide,
As 4 O
f)
is
,
When
.
the product
HPO
3,
completely, so
arsenic burns in air, arsenious
with antimony, Sb 4
;
O6
;
but
vanadium pentoxide, V 2 O 5 , is formed when the element or one of the lower oxides is heated in air. The pentoxides behave differently when treated with water. While O 5 and P 4 O 10 unite with water with a 2 and As 4 O 10 slowly hissing noise to form 3 3, is the reacts to produce H^AsO 4 , and probably 3 4 result of dissolving V O in water the corresponding 2 5
N
HNO
HPO
H VO
;
Sb 2 O 5
is
insoluble in water.
The
Acid Chlorides. acids of these elements in
is
clue to the constitution of the
afforded by the oxychlorides, as
the case of carbon and silicon.
taining pentad nitrogen
No
oxychloride con-
known, but phosphoryl chloride,
is
O=PC1 3 , and antimonyl chloride, O=SbCl 3 , are produced by the action of a small quantity of water on the C1 2 =PC1 3 + O = O=PC1 3 + respective pentachlorides 2
H
:
2HC1. and the
The
former
latter
a
is
a colourless liquid boiling at
white,
crystalline
solid.
107,
Phosphoryl
chloride reacts with hydrogen sulphide, yielding the corre-
sponding phosphoryl sulphide
+ H 2 O,
:
O=PC1 3 + H,S = S=PC1 3
and hydrogen
tachloride,
with
sulphide acts on formation of S=SbCl 3
antimony pen.
VO
O=VC1 3
is
It is a with chlorine. produced by direct union of The vapour-densities of yellow liquid boiling at 137. phosphoryl and vanadyl chlorides lead to the ascribed
formulae.
Ortho-, Pyro-,
and Meta-Acids.
With
water,
MODERN CHEMISTRY
i2 4
these
substances
O=PC1 3 +
3
exchange chlorine
H-OH
establishes the formula of
name ought,
for
hydroxyl, thus
- O=P(OH) 3 + sHCl.
The
ortho-phosphoric acid.
in strictness, to
be applied to
:
This
P(OH) 5
;
but,
as the true ortho-phosphoric acid is unknown, it has been transferred to what should be termed its first anhydride. have th\ nitric acid is unknown. The
We
corresponding
the
series:
O=PC1 3
O=P(OH) 3 O=As(OH) ,
,
3,
at
O=Sb(OH) 3 On heating these bodies the elements of water are lost, and .
the
" meta-acids "
are
formed;
at a
O
temperature of about
II
200,
O=P(OH) 8
yields
P-OH, O
and
O=As(OH) 3
,
O II
As -
OH
;
the
former
is
a
glass,
the
latter
a
pearly
II
O substance. it
dissolves
series
On as
adding such,
.
water to metaphosphoric acid on neutralisation, it yields a
and,
of metaphosphates
;
but
metarsenic acid, when
treated with water, is reconverted into orthoarsenic acid ; a similar change can be produced with metaphosphoric acid, but only after prolonged boiling. are unacquainted with Di" Acids.
We
any normal di-
acid of this group, but a number of anhydrides are known. If Z stand for any element of this group, the series should
run as follows
:
(OH) 2 =Z<-OH
/OH
/OH O=Z^OH
(OH),=Z<-OH
(OKL-Z^-OH
>o
\OH
Di-acid.
>o
\OH
1st
Anhydride.
PHOSPHORIC ACIDS O=Z /OH
125
OH
0\> \OH
O=Z OH
2nd Andryhide.
3rd Anhydride.
nor the first anhydride are known any case, but the second anhydride, which is generally called the "pyro" acid, because it is formed in certain " cases by heating the " ortho acid, is known with phosPyrophosphorus, arsenic, antimony, and vanadium. phoric acid is formed at 215; but the change is not complete, and if a higher temperature be employed the meta-acid is also produced. Pyroarsenic acid is formed
Neither the di-acid
in
Pyroantimonic by heating the ortho-acid to 140 1 60. acid, however, is best prepared by the action of boiling water on antimonyl chloride, O=SbCl 3 ; the ortho-acid, which is probably formed first, loses the elements of water,
H
Sb 2 O T forming the pyro-acid, Pyro-phosphoric acid 2 is a pyro-arsenic acid forms syrupy glass-like substance hard crystals, and pyro-antimonic acid is a sparingly soluble white powder. The basicity of these acids is deduced from Basicity. the formulae of double salts. Thus, there are three orthothey have the phosphates of sodium and hydrogen NaPO 4 , HNa 2 PO 4 and Na3 PO 4 the hydroformulae 2 HCaPO 4 , and gen calcium salts are: 4 Ca(PO 4 ) 2 , .
;
;
H
Ca 3 (PO 4 ) 2
H
,
;
It is therefore argued that since the hydrogen atoms of ortho-phosphoric acid are replaceable in three stages by metals, there are therefore three atoms of hydroThese salts are made by mixture 2H 3 PO 4 .Aq + gen. Na 3 PO 4 .Aq=3H 2 NaPO 4 .Aq, and so on. The acid is, The arsenates are precisely therefore, said to be tri-basic. but only simple vanadates are known, and no similar .
;
;
A
ortho-antimonates.
formula
HK (NH
4
pyrophosphate is known of the )P 2 O 7 which demonstrates the tetra,
MODERN CHEMISTRY
126
character of pyrophosphoric pyro-acids are classified accordingly. basic
acid,
and
the
other
Metaphosphoric Acids. The formula of the third Z O C given on the preanhydride of the di-acid, 2 ceding page, is a multiple by two of that of the metaacid, and it is evident that the fourth anhydride of the tri-acid, the fifth of the tetra-acid, and so on, will all be multiples of the simpler formula of the meta-acid. These acids and some of their salts appear to be known in the case of the phosphoric acids, and what is usually termed " meta-phosphoric acid," and given the formula is probably the seventh anhydride of hexa-phosphoric 3 P 6 O 18 , for one of its double salts has the formula acid,
H
HPO
,
,
H
ri
Na 2 Ca 5 (P 6
18 ) 2
.
salts are known in the case of almost all these elements. 9 Among such compounds are " 4 n, P 418 P while ni ba teS and g
Complex
:
A
A
HNO
V 6l
tantalates are particularly prone to form such Compounds of a complicated kind, too, in
complex salts. which one of
these elements replaces another partially, have been made ; as an example, may be instanced. .(P 8 12 )O 50 .2iH
K
V
salts
form
2
(
They are made by mixture. The source of the nitrates
is
O
the attack of
ammonium
from the decomposition of urea (the chief which all animals part with the nitrogen they
resulting in
absorb as a constituent of their food) by a bacterium named the " nitrate ferment." This organism exists only in the dark ; it is an inhabitant of the soil, and causes the oxidation of ammonia, from whatever source, into a nitrate. As potash and lime are the commonest bases in the soil, nitrates of potassium and calcium are the chief compounds formed.
Vast tracts of country in Chili and Peru contain beds of sodium nitrate, possibly formed by the attack of the debris of previous generations of animal organisms by the nitrate ferment. By distilling a mixture of sodium or potassium nitrate with sulphuric acid in glass vessels, or, on a large scale, in iron vessels on which concentrated nitric acid is
PHOSPHORIC ACIDS without action,
nitric
NaNO + H SO 4 = HNO 8 + HNaSO 4 3
127
acid comes over into the receiver .
2
It
:
not econo-
is
mical to use the equivalent quantity of sulphuric acid, for the reaction between hydrogen, sodium sulphate, and sodium nitrate takes place at a temperature so the nitric acid is decomposed :
+ O2
high that
much of
4HNO g = 2H O + 4NO
Nitric acid
.
is
a
very corrosive properties. the strongest acids, for it
powerful oxidising agent Its
p. 97.
anhydride,
2
fuming liquid, with In aqueous solution it is one of colourless
is ;
2
It is also a highly ionised. has been referred to on
this
NO 2
5,
produced on
is
distilling
a mixture of nitric acid with phosphoric anhydride ; the distillate separates into two layers ; the upper one consists
NO
mainly of
when
it
2
is
5,
cooled
and the anhydride separates the lower layer contains
in
crystals , a 4
H N On
;
2
5 ; it is the last anhydride of tetraliquid solidifying at The anhydride decomposes spontaneously in a nitric acid.
N
O 4 and oxygen. few days into the peroxide, 2 The nitrates are all soluble salts, possessNitrates. ,
As a rule, they ing the colours of their metallic ions. crystallise easily. They are all decomposed by heat ; those and of the metals of the alkalies into nitrite and oxygen all others into the oxide of the metal and nitric oxide and a d . peroxide, They are formed by dissolving 2 ;
NO
NO
f
the metal, the oxide, or the carbonate in dilute nitric acid. All metals are attacked by nitric acid, except gold and the The chief nitrates are those metals of the platinum group.
KNO
of potassium,
3,
saltpetre or nitre
of sodium, NaNO 3 from which 3,
;
Pb(NO 3 )." ?,
old
name
and
silver nitrate,
lunar caustic," the
AgNO"
3,
word
the ancient alchemical connection
moon. warts
still
lunar
between
;
lead nitrate,
known by "
its
referring to
silver
and the
used as a caustic for removing growths and metallic silver is deposited, blackening the place It
;
,
NH NO
Chili saltpetre ; ammonium nitrate, 4 nitrous oxide, N.^O, is obtained on heating
is
rubbed.
Phosphates.
The
source
of phosphoric acid and
MODERN CHEMISTRY
128
the
phosphates
a mineral
is
known
chiefly calcium as phosphorite,
phosphate,
A1PO 4
and
Ca 3 (PO 4 ) 2
,
aluminium produced from ,
Phosphoric acid is phosphate, or gibbs'te. phosphorite by heating it with dilute sulphuric acid ; sparingly soluble calcium phosphate is formed, while orthoThe solution, on phosphoric acid goes into solution. the evaporation, deposits white crystals of 4 g .H 9 ; comresidual liquor deposits crystals of g 4
H PO
H PO
;
O
mercial or "glacial phosphoric acid" is a mixture of both kinds. Its solution contains many hydrogen ions, and it is
therefore a strong acid.
But, inasmuch as phosphoric
+
HPO
and
of anions.
+
4,
H
and into
The
H PO 2
of these,
first
small relative amount
and
;
+
3H
acid can ionise in three ways, into
PO
zH
into
4,
there are three kinds
4,
PO 4
and
,
are present in very
HPO
the second and third,
and
4
H PO
are relatively much more numerous. There is a 4, of balance between the quantities of these ions present in and if, for example, kations of calcium or any solution lead or silver be added to a solution of phosphoric acid, or to one of hydrogen di-sodium phosphate, Na the 4 2 state
;
HPO
PO 4
,
ions present enter into combination with the kations,
forming
Ca 3 (PO 4 ) 2 Pb 3 (PO 4 ) 2 ,
,
or
Ag 3 PO 4
HPO
ions are increased at the expense of the ions, and the solution becomes more acid.
4
;
PO~4
the
and
H PO 9
4
On
adding an alkali, e.g. caustic soda, to a solution of phosphoric acid, has been reached; neutrality occurs when the salt Na. 4
HPO and HPO 7
+
. the ions are then mainly 2Na On adding 4 more soda, the solution becomes alkaline, indicating the
presence of free that these
OH
OH
ions
;
and
it
is
only on concentration
+
ions
combine with the few
H
ions of the
PHOSPHATES
129
+
+
HPO
non-ionised water, and " triNa 4 , forming sodium phosphate, Na g PO 4 , is left as a residue. Similar remarks apply to the ortho-arsenates. The ortho-vanadates are hydrolysed by water into pyro- and
ionised,
basic
"
meta-vanadates.
The
Na 2 HPO 4 .i2H.2 O,
chief orthophosphates are:
obtained by neutralising phosphoric acid with sodium carbonate ; named " microcosmic 4 )PO 4 .4H 9 O,
HNa(NH
the
salt";
"
human organism used
microcosm," and
urine
to
known
be
the
as
of concentrated Ca 3 (PO 4 ) 9 , prepared by precipitation, and found native
;
this salt crystallises out
,Ca-PO 4 =Ca
as
phosphorite
F
;
spread mineral termed
white
precipitate
magnesium ions
PO 4<^ a widely X Ca-PO =Ca 4 apatite (NH 4 )MgPO 4 .6H O, a
Ca
,
;
by
produced
adding
ammonium
to those of a soluble phosphate
Mg + PO 4 = (NH 4 )MgPO 4
It
.
and
+
is
:
(NH 4 + )
the usual test for the
presence of magnesia, and serves at the same time to disarsenates give a precisely similar ;
tinguish phosphoric acid precipitate.
The
precipitate
is
nearly insoluble
in
am-
moniacal water, and it may be filtered off and washed with water containing ammonia with very little loss. Like almost all phosphates, it is soluble in water containing hydrogen ions ; and by the addition of ammonium hydrOn ignition, oxide their number is greatly diminished. pyrophosphate, Mg P 2 (X, yields magnesium 2Mg(NH 4 )PO 4 = Mg 2 P 2 O + 2 NH 3 + H O.
it
9
7
thus
:
2
Arsenates. The important arsenates correspond exactly in formula and crystalline form to the phosphates ; the only striking difference is in the colour of the silver salt
;
while ortho-phosphate of silver
arsenate
is
is
yellow, the ortho-
brick-red.
Vanadates. Ortho-vanadates are prepared by fusing vanadium pentoxide with the required amount of a carbonate; VOL.
II.
I
MODERN CHEMISTRY
i3o
on addition of nitric acid to one of its salts, metavanadic on ignition, a acid separates out as a brown-red powder ;
sparingly soluble
VO 2
5
.
red powder
is
left:
2HVO 3 = H O +
Ortho-antimonates are unknown.
Thio- Acids.
Thio-compounds are known, analogous Mention may be made of mixed oxy-thiophosphates, e.g. Na 3 PO g S and Na 3 POS 3 , which result from the action of alkaline hydroxides on phosphorus pentasulphide, a grey solid produced by direct combination of phosphorus with sulphur. They are easily decomposed by hot water hence the thio-arsenates and the thio-antimonates are better known. Arsenious sulphide, As 9 S 3 a yellow precipitate formed by the action of hydrogen sulphide on a solution of arsenious chloride, and antimony trisulphide, Sb 2 S an 3 to these salts.
;
,
,
orange precipitate similarly formed, dissolve in solutions of polysulphides of the alkalies these solutions, on evaporation, deposit ;
crystals S( n
2)'
As 2 S 3 = 2K 2 S*.Aq = 2K g AsS 4 .Aq + Sodium thio-antimonate, Na g SbS 4 .9H 9 O, has long
on cooling
:
known as "Schlippe's salt." One of the sulphur atoms may be replaced by selenium, giving Na 3 SbS 3 Se.9H.,O, been
thus showing the similarity in and selenium.
Pyrophosphoric Acid.
character between sulphur
When
hydrogen di-sodium
orthophosphate is heated to redness, water is lost, and tetra-sodium pyrophosphate is left as a white deliquescent O. This salt is soluble mass : 2HNa 2 PO 4 = Na4 P 2 7 + 2 in water. On adding to it lead nitrate, a precipitate of
O
H
pyrophosphate is thrown down ; it is filtered off, suspended in water, and a current of hydrogen sulphide is Lead sulphide is formed, passed through the liquid. and, on removing it by filtration, the solution contains With silver nitrate, a pyrophosphate pyrophosphoric acid. gives a white precipitate of silver pyrophosphate, a reaction which distinguishes this acid from orthophosphoric acid, for silver orthophosphate is yellow. Magnesium pyrophosphate has already been alluded to. The pyrophosphates of the metals, those of the alkalies excepted, are insoluble lead
META-SALTS
131
water, but, for reasons similar to those given in describing the ortho phosphates, they dissolve in acids. in
Pyroantimonate of potassium
is a salt obtained by metantimonate, KSbO g , with caustic potash, and crystallisation of the resulting fused mass from water. It is easily soluble, but on adding its solution to that of a sodium salt, a precipitate of the sparingly soluble di-hydrogen di-sodium pyroantimoniate, Na 2 Sb 2 (X, is produced, It 2 is one of the very few sparingly soluble salts of sodium. On heating to redness di-hydrogen Meta- Salts.
the
fusing
H
sodium orthophosphate,
H(NH
4
)NaPO 4 .4H 2 O,
H
9
NaPO 4
water,
,
microcosmic
or
or,
in
the
case, residue consists of
ammonia in addition, is lost, and the sodium hexa-metaphosphate, (NaPO 3 ) 6 soluble in water
which
is
soluble it
;
its salts
salt,
latter
.
It
is
a glass
The
are mostly gelatinous.
acid,
probably also hexa-metaphosphoric acid,
glass,
yields salts
is
a
formed on igniting ortho-phosphoric acid like that mentioned on p. 126. Unlike the ;
two phosphoric acids, it coagulates a Its silver white-of-egg or albumen in water.
other
of white
solution salt is
and gelatinous. Mono-metaphosphates are insoluble salts, produced by igniting together oxides, carbonates, sulphates, or nitrates with excess of phosphoric acid, and removing the excess of phosphoric acid with water. The salts of the alkalies are sparingly soluble. Metarsenates are produced in a similar manner to the hexa-metaphosphates, but, on treatment with water, they combine with water and re-form the orthoarsenates of metal and hydrogen from
which they were obtained.
Some pyro- and
meta-thio-
arsenates have been prepared.
Compounds containing
less
Oxygen.
The
elements of the nitrogen group are characterised by their possessing more than one valency. They are also, in
most
of forming compounds with hydrogen. taken together, lead to the possibility of their forming a number of isomeric compounds, i.e. compounds having an identical composition, cases, capable
These two
characteristics,
MODERN CHEMISTRY
132
but being, at the same time, different chemical individuals. Some such compounds are known, at least in their de-
The conception will be clearer after inspection of the following table
rivatives.
:
HO X /OH >N^OH HCK \OH
HO X /H >N(-OH HO/ M>H
(i)
(2)
6=N^OH
\OH
(9)
TT
/**
\OH
IO )
/OH (16)
(15)
/OH
Nc-OH
X)H
/H
TT
/**
O-Ne-H
O=N(-H \H
TI
I2 )
\OH
(
,H
HO X
(4)
(3)
TT
0=NfOH (
/H
^NfH >N(-H HO/ \OH HO 7 X H
/*-*-
/~\"LT
/\JLL
HO X
)
PHOSPHOROUS ACID
133
may possibly be the formula of hydroxylamine its " name, in that case, should be oxy-ammonia." In all The other these compounds the element is a pentad. ever,
;
compounds contain
triad element.
(5) probably represents is an alternative formula for nitrites. (6) and (14) are unknown. (7) is an alternative formula for hydroxylamine. the formulas of the arsenites
;
1
(
We
Phosphorous Acid.
3
)
shall first consider
numbers
In phosphorous trichloride, PC1 3 , phos(8) and (16). On heating this compound phorus is undoubtedly a triad. to 60, and passing over it a current of dry air, and subsequently leading the air through ice-cold water, crystals separate, which are washed with ice- water and dried in a vacuum. . The acid, They have the formula 3 3 however, is di-basic ; the formula of its sodium salt, for
H PO
HPO
Again, phosphorous anhydride example, is Na 3 P 4 O produced by the combustion of phosphorus in a limited supply of air, constitutes a crystalline substance, it is acted on melting at 22.5 only very slowly by cold These facts point water, and then yields phosphorous acid. to a molecular change from P(OH) 3 to 2 But this view is rendered certain by consideration of the ethyl salts of the acids. .
,
;
O=PH(OH)
.
Constitution of Phosphorous Acid. solution of
trichloride, if treated with a in alcohol, 9 5) ,
Na(OC (C 2 It
H
is
5
H
a
or
of
tri-ethyl phosphite, to P(OH) . Corresponding 8 o On the other hand, a 191.
P(OC 2 H 5
liquid, boiling at analogous to
compound known,
2
);PO ?
Phosphorous sodium ethoxide,
yields
) 3,
PH
is hydrogen phosphide, g, formula named 5 ), 2 (C 2 di-ethyl which, on oxidation, yields a di-basic acid
the
PH
phosphine, analogous to phosphorous acid,
H
O=P(C 2 H 5 (OH) )
,
named
ethyl-phosphinic acid, from which the ethyl salt can be isomeric with ethyl prepared, O=P(C 2 5 )(OC 2 5 ) 2,
H
H
Ethyl phosphite is a derivative of triad phosphorus, whereas di-ethyl ethyl-phosphinate is derived from The anhydride of phosphinic acid, pentad phosphorus. phosphite.
i
MODERN CHEMISTRY
34
O II
O=PH(OH)
2,
would
P2O 3
not
be,
,
but
H-P=O,
like
But this substance is not formed on heating phos(16). phorous acid, for it decomposes into phosphoric acid and = . + 3H g phosphoretted hydrogen, thus: 3 3 4 3 One of the varieties of the salts of nitrous acid, however, has a corresponding formula. When a nitrate of one of the metals of the Nitrites. alkalies is heated with metallic lead, lead monoxide is
PH
4H PO
formed, and a
nitrite,
thus
:
KNO
PO
+ Pb= PbO + KNO 2
3
.
The nitrite is left as
a white fusible salt, easily soluble in water. acidifying a very dilute solution with sulphuric acid, a dilute solution of nitrous acid is formed ; but on warming it,
On
a
somewhat complex
action takes place. First, the anhy= 2 O.Aq + 2 O 3 next, produced 2 .Aq the anhydride is attacked by the water and decomposed O= and some of the anhy3N 2 O 3 + 3 + 4NO ; dride volatilises with decomposition into nitric oxide and
dride
is
:
H
2HNO
N
;
:
H
peroxide
:
2HNO
N O = NO + NO 9
3
easily soluble crystalline salts;
and
AgNO
The
.
are white,
nitrites
those of lead,
Pb(NO 2 )
,
are sparingly soluble. All are decomthe stronger acids ; for nitrous acid is a weak acid,
silver,
,
posed by and, moreover, it is easily decomposed, as has been pointed out. None of these changes throws any light on the constitution of nitrous acid, however. To gain this knowledge it is necessary to study the alky]
for example, ethyl Nitrites. Ethyl a mixture of sodium
salts
Constitution of the made by distilling together
;
nitrite. nitrite,
nitrite,
sulphuric acid, and alcohol, is a volatile colourless liquid On boiling it with a solution of with a fragrant odour. sodium hydroxide it is hydrolysed, the ethyl group being again replaced by the metal sodium, thus O(C 9 5 ) :
O=N
+ NaOH.Aq = O=N-ONa.Aq + C 2 H 5 OH.
H
And
if
ethyl nitrite be placed in a flask along with tin and hydroin other words, exposed to the action of chloric acid
nascent hydrogen
the products are
ammonia (with some
NITRITES
135
H H H O = N-HorO + N-H + H H H I
I
hydroxylamine) and alcohol
HO(C. H 5 ). ?
Sodium
O=N
the formula
:
therefore appears to possess silver nitrite, heated in a
nitrite
ONa.
I
But
sealed tube with ethyl iodide, yields a compound of the as, but not identical with, ethyl nitrite,
same composition
o II
and the formula
N
(C 2
H
ascribed to it;
is
5)
for,
on heat-
O it is not hydrolysed, but one of the atoms of hydrogen of the ethyl group is replaced by the
ing with caustic soda,
O ii
N
element sodium, giving
(C
H Na) 4
and further, with
;
II
O nascent hydrogen, the two atoms of oxygen are removed
and replaced by hydrogen, yielding ethylamine, a compound
H
analogous to ammonia,
N
(C
H
5)
;
this
shows that the
H ethyl group in the compound, which is named nitroethane, is in direct union with the It appears, then, nitrogen atom.
O
that
silver
nitrite
has
the
also
follows
formula
N
Ag,
and
not
6
O=N must
OAg. exist,
It
O=N OH
that
two
nitrous
acids
O and
N 6
H,
the
former
(13)
a
MODERN CHEMISTRY
136
derivative of triad, and the latter (16) of pentad nitrogen. But the acids are unknown, and it is only possible to guess the constitutional formulae of the salts through the reactions just described.
Arsenites, derived from the acid such as hydrogen cupric arsenite or " Scheele's green," HCuAsO 3 produced by adding to a solution of copper sulphate potassium arsenite, arsenious oxide, and a little ammonia ; As 9 5 , and pyro-arsenites, such as 4 also ortho- and meta-thioarsenites, metarsenites, ; AsS 3 and KAsS , are known. They show no signs of 3 isomerism like that of the phosphites and nitrites, and they
Arsenftes.
HgAsO 3
,
,
K
O
KAsO
K
are
doubtless
of
salts
and
As(OH)3
O=As OH,
and
the corresponding sulphur acids, although the acids correMetantimonite sponding to the sulphur salts are unknown.
NaSbO^, and meta-thioantimonite, NaSbS.,, are formed by dissolving antimonious oxide, Sb4 O 6 , or the sulphide, Sb.? S 3 , in caustic soda, and precipitating with alcohol. of sodium,
Hypophosphorous
Hypophosphites. is
a monobasic acid
Na(H PO 2 ). given in
(
1 1
).
;
H PO
acid,
3
2,
sodium hypophosphite has the formufa
This leads
When
to a formula analogous to that heated, too, the acid yields phosphine
PH
H
and phosphoric acid: 2H 3 PO 2 = PO 4 This 3 + 3 would lead to the supposition that some of the hydrogen was already in combination with the phosphorus. Its salts also yield phosphine, together with a phosphate and free hydrogen.
The
prepared by the action of sulphuric that salt is prepared by boiling 2? 4 phosphorus and caustic baryta
acid
is
acid on the barium salt
together
yellow
.
;
:
+ 3Ba(OH) 2 .Aq + 6H 2 O - 2PH 3 + 3Ba(H 2 PO 2
With
sulphuric acid insoluble barium sulphate while hypophosphorous acid remains in solution.
is
)
2
.Aq.
formed, It forms
The acid has reducing white crystals, melting at 17.4. power ; with silver nitrate, for example, metallic silver is With hydrogen precipitated and phosphoric acid is formed. iodide phosphorous acid and phosphonium iodide are formed
3H(H PO 2 ) + HI = 2H (HPO 3 + PH 4 I. 2
2
)
:
HYPOPHOSPHATES Two
acids are
known belonging
137
to this group of ele-
they have not been tabulated on p. 132, because their structure may be compared with that of hydrazine or
ments
;
H N NH
liquid phosphine,
9
2
or
H
2
P
PH
,
which two
in
atoms of nitrogen or of phosphorus are in direct union with each other. These are phosphatic acid, or, as it is
0=P=(OH) 2 sometimes termed, hypophosphoric acid,
",
I
0=P=(OH) N-(OH) and hyponitrous acid,
The
.
||
first
of these
is
N-(OH) produced in small quantity along with ortho-phosphoric and phosphorous acids, when phosphorus is oxidised by exposure to moist air. It is, however, best made from its silver salt, by addition of the equivalent quantity of hydrochloric acid. Silver hjpophosphate is produced by dissolving 6 grams of silver in 100 grams of nitric acid diluted with its own weight of water, and adding to the solution, warmed on a As soon as the waterbath, 8 or 9 grams of phosphorus. violent evolution of nitrous gases ceases the liquid is cooled, and silver hypophosphate crystallises out. The acid has no reducing properties, hence it probably contains no hydrogen capable of conversion into hydroxyl by the addition of The sodium salt, Na 4 P 2 O 6 , is converted into oxygen. pyrophosphate by the action of a solution of bromine in water the change is evidently due to the addition of J ;
O=P=(OH) 2 oxygen, thus
+O=
:
O=P=(OH) 2 O
.
The
I
O=P=(OH) anhydride of
this acid
O=P=(OH)
9
0=P=0
would be
;
a
2
compound of
O=P=O the formula
P2 O 4
of phosphorus
in
is
produced by the incomplete combustion
oxygen
;
but as
it
yields orthophosphoric
MODERN CHEMISTRY
138
and phosphorous acids on treatment with water, probability phosphoryl phosphate,
O=P~ O~ P^,
it is
in all
o .
^O
Hyponitrites are produced by the action of sodium amalgam, that is, a solution of sodium in mercury containing about 4 per cent, of the former, on a solution of potasAfter the mixture has stood for sium or sodium nitrite. some days, it is rendered slightly acid with acetic acid, and
A
added. yellow precipitate of silver produced ; other hyponitrites may be prepared from it by the addition of the calculated quantity of the respective chloride. The acid can also be liberated by the addition to a very dilute aqueous solution of the equivaOn warming the solution lent amount of hydrochloric acid. of the acid, nitrous oxide is evolved but nitrous oxide does not unite with water to form the acid. That the acid has the formula H.2 2 O 2 , and not HNO, is shown by its formation from hydroxylamine and nitrous silver
nitrate
hyponitrite
is
is
;
N
acid. On mixing dilute solutions of hydroxylamine sulphate and sodium nitrate, the hydroxylamine nitrate loses water,
thus:
HO-NH
the silver
salt is
2
+
O=N-OH = H O + HO-N=N-OH; 2
thrown down on addition of
silver nitrate.
CHAPTER
VIII
The Oxy-Acids of the Halogens; Perchlorates and Periodates ; Chlorates, Bromates, and lodates; Chlorites ; Hypochlorites, Hypobromites, and Hypoiodites Acids and Salts of Sulphur, Selenium, and Tellurium; of Molybdenium, Tungsten, and Uranium Perchromates, Persulphates, Perborates, and Percarbonates.
THE formulae of the acids of the halogens present some analogy with those of the nitrogen group, for, like the But while latter, the halogens also possess uneven valency. the highest valency of elements of the nitrogen group is that of a pentad, chlorine and iodine function as heptads in The valency of ihe halogens perchloric and periodic acids. is five in
acid
;
chloric, bromic,
and
one
nypoiodites. p.
A
and iodic acids
;
three in chlorous
hypobromites, and short table, analogous to that given on the
in
hypochlorites,
132, shows the relation between these compounds
I(OH)g(ONa), periodates
O=I(OAg) 5
corresponding
ortho-
,
to
O=I(OH) 5
,
para-
;
/>I(OAg) 3 corresponding ,
(
I(OH) r
;
corresponding
,
periodates
to
:
middle) periodates 139
;
to
/>I(OH) g meso,
I
MODERN CHEMISTRY
4o
O-I(OAg), O<^
O=;>I(OH), meta-
corresponding to
O^
periodates.
\
x^
O
0=7!
Perchloric
I^F=O,
acid,
unknown
O g Cl(OH),
periodic anhydride.
to
corresponding
meta-
periodic acid, is the only representative of these among But the the other members of the halogen group. periodates, like the phosphates, form still more condensed I acids ; thus, salts of a di-ortho-periodic acid, 8 2 n, I as well as of a and of a di-meso-periodic acid, 4 2 9, tetra-
are
and hexa-periodic
acid,
H O H O 10
I
4
19
H O H IO
and
90
6
91 ,
known.
T(OH) 5
,
ortho
chloric acids are
O=I(OH) 3
,
iodic
acid;
and
orthobromic
unknown. and similar bromine and chlorine
ortho
acids, are
unknown.
Br(OH), and
I(OH),
Cl(OH),
iodic,
bromic, and chloric acids.
\/,\
^
O
Iv\
^o
cr hydride known.
A tri-iodic
,
iodic
anhydride,
is
the
only
an-
HI 3 O g , has been prepared. chlorous acid, is the only representative
acid,
O=C1 (OH), of triad halide.
I-(ONa), Br-(ONa), and Cl-(ONa), -chlorite, and -bromite of sodium metals are fairly stable in solution.
Hypoctllorites.
The
hypoiodite, other
and of some
starting-point
for
these
com-
pounds is the hypohalite it is produced by the action of a hydroxide on the element in cold aqueous solution, thus : ;
HYPOCHLORITES 2NaOH.Aq + Cl.,, + H,O + NaOCl," NaOBr, Br 9
Chlorine
,
or I,
monoxide,
= NaCl,
141
NaBr,
or
Nal.Aq
on
passing
NaOI. Aq.
of
C1 2 O,
is
formed
over dry mercuric oxide, prepared by precipitation from mercuric chloride with caustic soda, dry chlorine gas the tube containing the oxide must be cooled with ice, for the ;
monoxide
is
at
6.
TJie
Cl
O
a
dark brown, very unstable liquid, boiling equation
2HgO + 2C12 = Hg 2Cl.,O +
is:
10 corresponds with the formula If the mercuric oxide be made into an emulsion
Cl.
given.
Its density at
with water, and chlorine be passed through, the acid is it is a produced in aqueous solution pale yellow liquid, If with a not unpleasant smell, recalling that of chlorine. concentrated, it decomposes into water, chlorine, and oxygen. It reacts at once with hydrochloric acid, forming water and ;
chlorine
:
H-O-C1. Aq + H-Cl.Aq = C1.2 + H,O. Aq.
The most
important hypochlorite is a double compound, obtained by the action of chlorine on slaked lime, termed " chloride of lime " or " bleaching-powder." It is a white, non-crystalline powder, smelling of hypochlorous acid. Its formula is Cl Ca Cl. That it is a compound, and
O
not
a
mixture of calcium
chloride and hypochlorite,
is
proved by the fact that bleaching-powder is not deliquescent, whereas calcium chloride is a very deliquescent salt; calcium chloride and hypochlorite are both very soluble salts, but bleaching-powder is only sparingly soluble, but if a saturated solution of bleaching-powder be cooled, crystals of hypochlorite separate out, thus proving that it is dissociated in aqueous solution into these two
salts.
Its
smell, as well as
due to the fact that hypoacid, and is only slightly ionised hence the calcium and other salts are hydrolysed by the ions of water, and the solution contains free base and free acid and the latter reveals its presence by its smell. No ion has a smell hence one does not smell solutions of
that of other hypochlorites, is chlorous acid is a very feeble ;
;
;
salts,
but only volatile non-ionised compounds.
When
bleaching-powder
is
distilled
with
just
enough
MODERN CHEMISTRY
i42
acid to liberate the hypochlorous acid, that acid comes over ; but if excess of such an acid as sulphuric or hydrochloric
be added, chlorine is liberated, owing to the reaction between hydrochloric and hypochlorous acids. The addition of a trace of a salt of cobalt to bleaching-powder results in the liberation of oxygen when it is warmed ; this reaction, which is termed " catalytic," is supposed to be due to the alternate formation and decomposition of an oxide of cobalt but the reaction is still obscure. of the formula Co 4 O 7 ;
The
bleaching action of bleaching-powder in presence of acid is ascribed to the liberation of oxygen, and the oxidation thereby of the insoluble brownish colouring matter of unbleached cotton or linen to soluble compounds which can
be removed by washing. Chlorates. Hypochlorites, when heated, undergo conversion into a mixture of chlorate and chloride :
3NaOCl.Aq = NaClO 3 .Aq + zNaCl.Aq. method of preparing
chlorates, however,
The
usual
to pass a current that is, calcium
is
" of chlorine through hot " milk of lime hydroxide suspended and partially dissolved in water. Potassium chloride equivalent to one-sixth of the lime is also present. The following reaction occurs 6Ca(OH) 9 .Aq :
+ 2KCl.Aq + 6C1 2 = 6CaCl 2 Aq + 2KC1O,. Aq + 6H 2 O. On evaporation, the sparingly soluble potassium chlorate de.
posits in crystals, leaving the very soluble calcium chloride in solution. The potassium chlorate is purified by recrystallisation.
It
is
a white, lustrous salt, crystallising in
flat
plates.
somewhat higher temperature than evolves oxygen. At the same time some
It fuses readily, and, at a its
melting-point,
of the chlorate is
formed:
KC1O 4
is
it
oxidised by the oxygen, and perchlorate
2KC1O 3 = 2KC1 + 3O 2
Perchlorates. after
,
and
KC1O 3 + O =
.
the salt has
On
ceasing to apply heat, therefore, pasty, and treating with water, dissolved, leaving the much less
become
the potassium chloride is soluble perchlorate ; the perchlorate recrystallisation.
may
be purified by
CHLORINE PEROXIDE to
Owing
143
very few potassium
the fact that
salts
are
insoluble in water, it is not convenient to prepare chloric acid from the potassium salt ; for this purpose it is
and chlorine
barium
the
use
to
better
a
;
solution
salt,
of this
made from baryta-water salt, when mixed with
the equivalent amount of dilute
by
sulphuric
acid, yields
a
barium sulphate, and chloric acid remains in
precipitate of solution.
Chlorine Peroxide. The solution, freed from barium filtration, may be concentrated by distilling away the
water
low temperature
at a
in a
a colourless, syrupy liquid, into perchloric acid, water and as
the
last
compound
is
vacuum the acid remains which decomposes at 100 ;
chlorine peroxide,
unstable at
C1O 2
;
temperature, and But the peroxide may
that
explodes into chlorine and oxygen. be prepared by warming, not above 40, a mixture of potassium chlorate and concentrated sulphuric acid ; the chloric acid decomposes
H O + 2C1O
as
is
it
formed:
3HC1O 3 = HC1O 4 +a
dark red liquid, boiling at io.6 Unlike nitric peroxide, it does to a reddish-brown gas. C1 2 O 4 is unknown. not form double molecules It resembles that compound, however, in its action on water while nitric peroxide gives a mixture of nitrous and nitric acids, chlorine peroxide, added to an alkali, forms a chlorite 2C1O 4- aKOH.Aq = KClO 9 .Aq + and a chlorate 2
2
It
.
is
a
;
;
:
KClO 3.Aq. The
in
water
chlorates, like the nitrates, are all readily soluble lead and silver chlorites, like the corresponding ;
sparingly soluble salts ; and lead perchlorate is the only salt which does not easily dissolve. As already mentioned, chloric acid is readily decomposed when its aqueous solution is warmed ; chlorous acid is still less stable ; but perchloric acid, which may be prepared by nitrites, are
distilling together
distilled
is
acid,
sulphuric
potassium perchlorate with concentrated relatively stable, seeing that it can be
without decomposition.
acid taste
;
it
is
apt to explode
It
is
an oily liquid, with
when brought
into contact
MODERN CHEMISTRY
144
The
with any oxidisable matter. acid
corresponding perbromic
unknown.
is
Hypobromites. Hypobromites are produced, along with bromides, on mixing solutions of alkalies with bromine ; the solution turns yellow, and acquires a smell like that of On warming, a change analogous to that suffered seaweed. by hypochlorites occurs; the hypobromite yields bromide and bromate, and the latter can be separated by crystallisation.
Bromates.
The bromates
are white salts soluble in
they do not, however, decompose into bromide and perbromate when heated ; the perbromate is unstable, and Bromic acid, bromide and oxygen are the only products. too, when warmed changes to water, hydrobromic acid, bromine, and oxygen ; as no compound analogous to C1O 2 is produced, bromous acid is unknown.
water
;
The
Hypoiodites. analogous
to
that
of
of
formation
hypochlorites
;
hypoiodites
but
the
salts
is
are
known only in solution mixed with iodide. Again, like the hypochlorites, they change on heating ; they yield a mixture of iodide and iodate ; and from barium iodate But iodic acid can be prepared. by boiling iodine with nitric acid
more readily obtained for iodine is more easily
it is ;
oxidised than either chlorine or bromine ; or chlorine and water may be used as an oxidising agent. Iodic Acid. Iodic acid is a white crystalline comit is a strong acid, and its pound, easily soluble in water salts are produced by neutralisation with hydroxides or When it is mixed in solution with hydriodic carbonates. acid, mutual decomposition ensues and iodine is liberated : ;
HIO 8 Aq + 5HI. Aq = 3 T + 3 H .
2
The
Periodic Acid.
2
O. Aq.
of iodic acid to periodic acid is accomplished by means of a solution of it is easier to dissolve sodium hypochlorite iodine in a solution of sodium carbonate, when hypoiodite is formed, The iodate at and to saturate the solution with chlorine. first formed is converted into the NaIO 3 .Aq + periodate oxidation
;
:
THERMAL DATA NaOCl. Aq = NaCl. Aq + NaIO 4 Aq.
145
As
the periodate is sparingly soluble in water, it crystallises out on concentratOn mixing the solution of the sodium ing the solution. -
salt is
with
silver
precipitated
;
nitrate, it is
tri-hydrogen di-argentic periodate dissolved in hot dilute nitric acid and
when mono-argentic periodate, AgIO 4 crystalOn mixing with water, this salt undergoes the 2AgIO 4 + 4 H 2 O = H 3 Ag 2 IO 6 + H 5 IO 6 .Aq.
evaporated, lises
out.
change
The
:
,
which is insoluble in water, is removed by and the periodic acid deposits in crystals on The acid forms white prisms on heating it evaporation. to 130, it decomposes into iodine pentoxide, I 2 O , a 5 white solid, also produced on heating iodic acid to 170, at 1 80 the pentoxide together with water and oxygen decomposes slowly into iodine and oxygen. Thermal Data. From the short description which has been given, it is seen that the oxides of iodine and their compounds are, as a rule, more stable than those of bromine and chlorine, and this is connected with the heat which is This heat is evolved or absorbed during their formation. seldom determined directly ; never when the compounds are produced with absorption of heat. Thus, when chlorine combines with oxygen to form C1.,O, enough heat is absorbed to cool 17,800 grams of water through i, or what is the same thing, on decomposing C1 2 O heat enough is liberated to raise the temperature of 17,800 grams of This is termed the heat of formation water through i. The heat of formation of chloric of the substance. acid from chlorine, oxygen, and water involves a heatabsorption of 20,400 calories, and these substances are silver salt,
filtration,
;
;
both very unstable. On the other hand, the combination of iodine with oxygen is attended with an evolution of heat of 25,300 calories, and an additional 2600 calories are liberated when it combines with water to form iodic acid. Perchloric acid, too, is formed with evolution of heat (4200 calories), and thus iodic, periodic, and perchloric
VOL.
arid are II.
comparatively stable.
The
heat-change K
MODERN CHEMISTRY
146
during the formation of a
with the
its
two
compound, therefore, is connected although the exact relationship between
stability, is at
present
unknown.
Acids derived from Elements of Even Valency. Elements of the molybdenum and of the sulphur groups can act as dyads, tetrads, and hexads, and there are corresponding compounds of chromium, manganese, and iron, while sulphur and manganese are also able to form compounds analogous in formula to the perchlorates, termed the permanganates and persulphates. Compounds in
which these elements function
as dyads, however, have no acid properties ; in the case of chromium, manganese, and iron, the dyad oxides have more or less basic properties
hydroxides are ionised into element and and they therefore form salts with acids. The oxides MoO 2 and 9 are also feebly basic in character, that
their
is,
hydroxyl
UO
TeO 9 but MnO 2 is the anhydride of a feeble acid, and SO 2 and SeO 2 form well-defined acids, sulphurous, H SO 3 and selenious, H 2 SeO g Oxides of Sulphur, Selenium, and Tellurium. as well as
;
.
,
2
When sulphur, selenium, the element takes fire and burns ;
The corresponding Acids. or tellurium
is
heated in
air,
the chief product in each case is the dioxide. That of sulphur is a colourless gas, possessing the well-known odour
of burning sulphur it
freezes at
;
-79.
condensable to a liquid at 8, and gas is soluble in water, uniting
it is
The
H
SO 3 on cooling the solution with it to form the acid, 2 6 and saturating it with the gas, crystals of the formula to SO 3 .8H 2 separate this is a hydrate of sulphurous 2 Selenious anhydride, a white solid, also dissolves in acid. water, and from the solution selenious acid crystallises It would naturally be SeO 3 out, with the formula 2 imagined that these acids should have the structural formulas OS=(OH) 2 and O=Se(OH) 2 , inasmuch as the oxides
H
O
;
;
H
are
O=S=O
O=S=C1 2 rides,
are
and
O=Se=O
.
;
moreover,
the
chlorides
O=Se=Cl,, thionyl and selenosyl known and these react at once with and
;
chlo-
water,
ISOMERIC SULPHITES
147
It is to be presumed that there is exforming the acids. change of chlorine for hydroxyl, as usual: 0=8=01.,+
2HOH
- O=S=(OH)., + 2HC1.
But
there
evi-
is
dence, similar in kind to that adduced in the case of nitrous and phosphorous acids, to show that while sodium sulphite has the formula
O=S=(ONa) <\ /Ag
expressed by
^S<^
O^
silver
,
sulphite
better
is
sulphur being a hexad.
,
X)Ag
SulIsomeric Sulphites. The evidence is this " merphur alcohol or ethyl-hydrosulphide (also termed captan"), when oxidised by boiling with dilute nitric is into thus : converted acid, acid, ethyl-sulphonic :
o i!
= C 2 H 5 S-OH,
monobasic
a
of
acid,
O
H
II
which the ethyl
salt is
C H.
S
O C
5
Now
.
sodium
6 sulphite,
warmed with
ethyl iodide, yields an isomeric
O C H -O-S-O-C H
com-
II
pound of the formula 2 5 2 known, because when saponified by boiling with
5
This
.
alkali, it
is
is
con-
O II
/OK + 2KOH=2C,H.OH + O=S\ X OK oniiication
of
ethyl
sulphonate
OC
C.,H-O S
verted into alcohol and a sulphite, thus:
;
yields
whereas
the
potassium
o
and
alcohol,
thus:
C.,H 5 S II
O
O
sap-
ethyl-
li
sulphonate
H,
C.2
H
g
+
MODERN CHEMISTRY
i 48
O KOH - C 2 H 5-S-OK + C 2 H OH. O
And, moreover,
5
this
I!
acid,
when
with phosphoric chloride, yields an
distilled
O
acid
C
chloride,
H
S Cl, which can be reduced with
5
O nascent hydrogen to ethyl hydrosulphide, the substance from It is which the acid was originally obtained by oxidation. therefore concluded that the carbon
is
directly united to the
sulphur atom in this case, while in ethyl sulphite the carbon It follows of the ethyl group is united through oxygen. that sulphurous acid
must have the formula O=J
X)H
whereas sulphonic acid should be represented by
The
silver
a sulphite. tellurium.
salt
is
a sulphonate, while the potassium salt
is
peculiarity is not shown by selenium or It appears certain that they are represented by
This
X)H
the
^S^ O^ X)H
formulae
.OH
and
O=Se<^
X)H
O=Te/
\OH
;
but
it
is
known which formula is to be ascribed to a solution of sulphur dioxide in water. Sulphites. The sulphites, selenites, and telluritesof the alkalies are soluble salts; those of most of the other metals Double salts with hydrogen are sparingly soluble in water. (" acid salts ") are, however, soluble, e.g. calcium hydrogen and they are all decomposed by the sulphite, Ca(HSO 3 ) 2
not
;
stronger acids, sulphurous acid being liberated, if the solution is dilute ; if strong, sulphur dioxide, its anhydride, comes off in the state of gas. Similarly, selenious and tellurous
ACID CHLORIDES
149
acids are liberated on addition of a strong acid to a solution of a selenite or tellurite. Pyrosulphites, similar in kind to
O
KO
O "
'I
O
S S OK, crystallise pyrophosphates, such as out on passing a current of sulphur dioxide through a solution of the carbonate of the alkali.
Sulphurous acid is a reducing agent, depriving reducible compounds of their oxygen it itself is oxidised to sulphuric acid by the process. Owing to this property, it is used to bleach woollen goods this it does by converting the insoluble colouring matter into a soluble colourless compound, which can be removed by washing. It is also an antiseptic and sulphites are added to liquors undergoing fermentation, ;
;
;
when
it is desired to check the action of the ferment. Selenious and tellurous acids, treated in boiling solution with sulphurous acid, deposit selenium or tellurium, thus SeO 3 .Aq + 2H,SO 3 .Aq = Se + 2H 2 SO 4.Aq + 2 O ; 2 and with sulphuretted hydrogen, sulphurous acid gives a :
H
H
precipitate
of
sulphur
H
:
2
SO 3 .Aq + 2H 2 S.Aq =38 +
This brings to mind the mutual action of hydrochloric and hypochlorous acids, and of hydriodic and iodic acids, where the elemens are also liberated. Acid Chlorides. Sulphur dioxide combines with chlorine when a mixture of the two gases is exposed to
2H.2 O.Aq.
sunlight, or
when
is
it
passed over gently heated charcoal.
o. The
product, sulphuryl chloride,
fuming liquid, boiling at 7 7. diately yields sulphuric acid
O NX
byhydroxyl:
/Cl
^S<
O^
+
ci
/>S\
O^
>
is
a colourless
NCI
On adding it to water, it immeby replacement of the chlorine O. x HC1
H OH /OH = ^S< + H OH O^ \OH HC1
\C1 Selenium and tellurium form similar compounds and so also do molybdenum, tungsten, and uranium, as well as chromium. Molybdyl, tungstyl, a-nd uranyl chlorides ;
MODERN CHEMISTRY
150
by passing chlorine over the dioxides heated they are not decomposed by water, but when boiled with alkalies they are converted into molybdates, Chromyl chloride, on the other tungstates, or uranates. hand, is formed by distilling together a chromate, a chloride, and concentrated sulphuric acid. This amounts to the action of hydrogen chloride on chromium trioxide, thus CrO 3 + 2HCl = CrO 2 Cl 2 + 2 O. The presence of the sulphuric acid is necessary in order to withdraw and retain water, for chromyl chloride is at once attacked by water, chromic acid being formed. It is a deep red fuming liquid, are produced
to redness
;
:
H
hardly distinguishable from bromine in appearance ; it boils 1 1 8. manganyl chloride is said also to have been
A
at
prepared.
The
constitution of the acids
and
is
inferred from that of the
the case of chromium, an intermediate body is known between chromyl chloride and potassium chromate, termed chlorochromate ; its formula is chlorides
;
;
in
with
the
sulphur,
OK
corresponding
chlorosulphuric, or, better, chlorosulphonic acid
O^
/Cl
o^/S\NOH
These bodies
are produced
is
acid,
known,
by the method of
mixture; the former by crystallising together anhydro-chro-
^O
CK mate and chloride of potassium
CK
+ KC1 =
O^
+
yCr\
X)K KCX /OK the
/OK O^
^Cr< O^ \OK
,0
.
}>Cr^
:
^Cr< O-^ NCI
;
latter,
V)
by the
union of hydrochloric acid with sulphur trioxide, thus
S
= O + HC1 =
red crystals
;
/ S\
the latter
:
OH
O.
is
a
'
fuming
The former
consists
liquid, readily acted
of
on
CHROMATES
151
by water, with formation of sulphuric and hydrochloric acids. have thus with sulphur and with chromium the series
We
:
0.x
/OH
0.x
,C1
C1
0.x
AH
O-
X)H O
OK
\C1
The starting-point for the chromates is It iron ore, Fe(CrO 2 ) 2 , a spinel (see p. 100). heated in a powdered state with a mixture of lime and Chromates.
chrome is
potassium carbonate, in a reverberatory furnace, where the The product is a atmosphere is a strongly oxidising one. mixture of calcium and potassium chromates and ferric
oxide
:
2Fe(CrO.2 ) 2 + 4K 2 CO 3 + 70 = Fe 2 O 3 + 4 K 2 CrO 4 The fritted mass is treated with water, when
+ 4CO 2
.
the chromate dissolves, leaving the ferric oxide- insoluble. On evaporation, potassium chromate crystallises out. If
"
"
desired to produce or anhydrochrobichromate mate of potassium, K Cr O^, the solution of the chromate is treated with dilute sulphuric acid ; calcium sulphate is precipitated, and is removed by settling ; on evaporation, sparingly soluble sulphate of potassium crystallises cut ; and after removal of the crystals, on further evaporation, " bi" chrome The conversion of the chromate into crystallises. it is
the
anhydrochromate
2 K,CrO
4
.
is
represented
Aq + H 2 SO 4 Aq = K .
This conversion
is
.,
Cr 2 O 7
by .
the
equation
accompanied by a colour-change
the ions of chromate,
CrO 4
,
:
Aq + K 2 SO 4 Aq. .
;
for
are yellow, whereas those of
On addition of anhydrochromate, Cr.,0^, are orange. potassium hydroxide to the bichromate, the opposite change takes place ; the anhydro-chromate ion is changed into the chromate ion
+ H 2 O.
:
K
2
Cr 9
-.
Aq + iKOH.Aq = 2K.,CrO 4 .Aq
MODERN CHEMISTRY
152
Chromic Acid.
Chromic acid
is
liberated on add-
ing to a concentrated solution of potassium anhydrochromate a sufficient excess of sulphuric acid : K.,Cr 2 7 . +
H
2
SO 4 = K 2 SO 4 Aq + H 2 O + 2CrO 3 .
centrated solution, loses water, and
O Aq
The
acid, in condeposits the trioxide or red colour. Chromium .
in crystals of a deep a powerful oxidising agent ; hence it may not be brought into contact with filter-paper ; it must be filtered The excess of through a mat of asbestos or glass wool.
anhydride trioxide
is
sulphuric acid and potassium sulphate are washed out with concentrated nitric acid, in which the anhydride is almost insoluble
the nitric acid
;
This anhydride dissolves the acid
H CrO 9
then volatilised by gentle heat. it is doubtful whether
contained in the solution
is
4
is
in water, but
;
more
is
it
+ +
HH
and Cr 2 (X, from the colour, probable that the ions are and other tests, such as the conductivity. Oxidation by means of a solution of chromic anhydride carried out either by boiling the substance to be oxidised with a mixture of bichrome and dilute sulphuric acid, or with a solution of chromic anhydride in pure acetic acid ; is
chromate
the
ion,
+++ chromic
+
4H
ion
- -
Cr
CrO 4
or
;
the
Cr 2 (X, action
+++
+
is
changed + - -
is: - -
K
into
the
Cr 2 O r Aq + 2
S0 4 .Aq = Cr 2 (S0 4 ) 3 .Aq + K 2 SO 4.Aq + 2
4
HO 2
+
hot and concentrated, oxygen substances present in solution, if they are capable of being oxidised, are attacked by the When chromic anhydride is heated, it is conoxygen. verted into chromium sesquioxide, Cr 9 3 , with evolution
30.
is
If the sulphuric acid
evolved as gas
;
is
if dilute,
O
of oxygen.
Manganates.
Oxides of manganese,
if
heated with
caustic alkalies in a current of air, or with potassium or sodium nitrate, are converted into manganate ; the manga-
however, is much more easily decomposed than the chromate, and, indeed, is stable only in presence of excess nate,
PERMANGANATES
153
incapable of existence ; an Manganic attempt to liberate it, by addition of an acid to its sodium salt, results in the formation of a permanganate and a
of
acid
alkali.
is
thus: 5Na 2 MnO 4 .Aq + 6H 2 SO 4 .Aq = MnSO HMnO 4 .Aq + 4H 2 O. + 5Na,SO 4 .Aq 4 .Aq + 4
manganous
salt,
Permanganates. While the manganates are bright green, the perm? % .nates, which are analogous to the perchlorates, are almost black ; they dissolve in water with a deep purple colour ; the best known is the potassium salt, a solution of which is sold under the name of " Condy's Fluid." It is also a useful oxidising agent. If an oxidisable body is boiled with its solution, it loses oxygen, thus :
KMnO 4 .Aq + 3 H O = 2KOH.Aq + 2MnO(OH) + 3O if an acid, such as sulphuric acid, present, the 2KMnO 4 .Aq + 3H SO 4 .Aq = K SO 4 .Aq + equation 2
2
2
is
;
is
:
2
2
Ferrates are
also
known
;
they are
than manganates.
still
more unstable
A
word may be added Equations Simplified. here with regard to the somewhat complicated equations It is convenient to assume the existsuch as those given. ence of the anhydride of the acid as a constituent of the salt ; thus potassium bichromate may for this purpose be in union with 2CrO . On regarded as consisting of 2 ? acting on it with sulphuric acid in presence of an oxidisable 9 may be supposed to react with the acid compound, the thus: + 2"SO 4 = K 2 SO 4 + 2 O. The chromium 2 salt formed may be regarded ( and this was formerly the point of view) as a compound of 3>SO 3 , the anhydride of sulphuric The acid, with Cr 2 3 viz., Cr 2 ;r 3SO 3 , or Cr 2 (SO 4 ) 3 . formation of Cr 2 3 from 2CrO 3 involves the loss of 30 ; hence the equation given above. Similarly, the oxidising action of potassium permanganate may be formulated thus :
KO
KO KO H O
H
O
,
O
K O.Mn O = K O + 2MnO + 30 and K O.Mn O = K O + 2MnO + 5O. With water present in the former action, the K.,O becomes KOH, and the manganese dioxide 2
2
7
2
2
;
2
2
7
2
becomes hydra ted
;
with sulphuric acid present in the
latter,
I
MODERN CHEMISTRY
54
converted into K.,SO 4 and the MnO into This old method of representing chemical changes had much to recommend it on the score of simpli-
K. O MnSO 4
the
is
7
,
.
city
and
;
it
often
is
found convenient, although
it
is
only
a partial expression of the truth.
Molybdates, Tungstates, and Uranates. formulae of the are analogous
K MoO Na 4,
2
molybdenum
to
2
is
The
molybdates, tungstates, and uranates those
WO
of the chromates
(NH 4 2 UO 4
4,
)
.
for
;
example, ore of
The common
the disulphide, crystalline scales resembling
On
heating it in graphite, MoS.,, termed molybdenite. the air, or on boiling it with concentrated nitric acid, it is oxidised to the trioxide, a white slippery powder. ,
MoO 3
Wolfram,
(Fe,Mn)WO 4
,
the chief ore of tungsten; on
is
boiling with concentrated nitro-hydrochloric acid, calcium nitrate and chloride go into solution, and tungstic acid,
WO
On yellow powder. the anhydride, a . Pitchblende is the powder with similar colour, g name of the commonest ore of uranium ; its formula is On fusing it with a mixture of nitrate and car3 8 is formed ; and on bonate of soda, sodium uranate Na 2 4 H.
7
heating
UO
4,
it,
remains it
as
loses
an insoluble
water, and
yields
WO
.
UO
H UO
is 9 adding acid, uranic acid, precipitated, as a 4 On heating it to 300, a scarlet powder, yellow powder. of the formula remains. Ignition changes it into 3, of the same uranium uranate, 3 4) , g , possibly formula as the natural mineral. The chief molybdate is that of ammonium, (NH 4 ) 2 white crystals obtained 4, by dissolving the acid in ammonia solution ; it is used in precipitating phosphoric acid as phospho- molybdate of ammonium, a representative of many very complicated molybdates ; its formula is i6MoO .P 2 5 .3(NH 4 ),O.i 4 ; 2 3 it is a derivative of one of the condensed molybdic acids.
UO
UO
U(UO
4>
MoO
O
Sodium tungstate,
NaaWO
HO
produced by fusing the triused as a mordant in dyeing, and it has the property of rendering cotton and linen The chief characteristic of uranium fabrics uninflammable. oxide with sodium carbonate,
4,
is
SULPHUR TRIOXIDE trioxide nitrate,
of forming uranyl
that
is
(UO )(NO 8 ) 2
and
,
salts,
acetate,
o
155
such as uranyl
(UO,)(C
H
3
O.
)
)
,
II
where uranyl,
U=
are ill-defined
compounds.
acts as a
dyad
The
radical.
uranates
O The constitution of sulphuryl conversion into sulphuric acid has already been alluded to. And it may be assumed that that of sulphur
Sulphur Trioxide.
chloride and
trioxide,
its
SO 3
,
is
expressed by the formula
^
O=Sx^
,
sulphur
acting as a hexad.
Although sulphur dioxide unites directly does not combine with oxygen, unless the two gases are brought intimately into contact by passing them over iinely divided platinum ; such platinum is best prepared with chlorine,
it
by dipping asbestos (a native magnesium silicate, possessing a fibrous structure) into platinic chloride, and subsequent ignition, when the chloride is decomposed into chlorine,
which escapes, and a deposit of spongy platinum on the asbestos. a large scale, sulphur dioxide, made by
On
burning sulphur or iron pyrites, FeS 2 , in air, is concentrated by solution in water, the gas being forced in under some pressure ; the solution, on being exposed to reduced pressure, gives up the gas,
which
the atmosphere.
The
is thus freed from the nitrogen of sulphur dioxide is then mixed with the platinised asbestos heated to a
and passed over Combination ensues, and the high temperature. It is a sulphur trioxide is condensed in cooled receivers. air
definite
white, crystalline, fuming substance, dissolving in water with a hissing noise and with great evolution of heat. It also unites directly with hydrogen chloride, with formation of chloro-sulphonic acid, Cl SO OH, a fuming very corrosive liquid.
Sulphuric Acid. irioxide in
water
is
The
product on dissolving sulphur
sulphuric
acid,
H
2
SO 4
;
if
smaller
i
MODERN CHEMISTRY
56
quantities
of water
formation of acids
are
HO
(SO
H.
>
SO 4
be used than are ,
necessary
for
the
pyro- or anhydro-sulphuric simplest of which is the acid,
various
produced, the
O (SO 2 )OH, analogous to some extent in for) mula to pyfophosphoric acid, ( ) ,=PO-O-PO= ( ) 2, but more closely resembling potassium dichromate. It, too, is a fuming liquid, evolving much heat on addition of
OH
OH
water.
Sulphuric acid, however, is ordinarily made by bringing together sulphur dioxide in presence of steam with nitric
NO
For this purpose, sulphur 9 , and oxygen. or iron pyrites is burned in air ; the products of combustion are passed through a flue provided with a chamber in which it is possible to place, when required, a pot containing a mixture of sodium nitrate and sulphuric acid ; the product
peroxide,
nitric acid, which is at once attacked by the sulphur dioxide, yielding sulphuric acid and nitric peroxide, thus : = 2 4 . The gases next pass 2 3 + 2 a termed the " Glover tower," after its inventor. tower, up
is
2HNO
SO
H SO +2NO
In this tower they meet a spray of dilute sulphuric acid, the decomposition product with water of a compound which will afterwards be alluded to, hydrogen nitrosyl sulphate. The hot gases, in contact with the dilute acid, evaporate much of its water, which as steam finds its way along with them up the tower. From the Glover tower the gases enter the first of a series of leaden chambers, in which a reaction occurs between the sulphur dioxide, the nitric = + SO 4 peroxide, and the steam, thus SO., + + NO. Excess of air is admitted along with the sulphur dioxide, so that there is present in the leaden chamber a :
NO
HO H
considerable excess of oxygen. By its aid, the nitric oxide is re-oxidised to peroxide, which is again attacked by the sulphur dioxide, so that the nitric oxide serves as a carrier
of oxygen to the sulphur dioxide.
The
nitrogen of the air
conveys the gases from chamber to chamber ; and when it has passed through a sufficient series (from nine to thirteen) of chambers, all the sulphur dioxide has been converted
SULPHURIC ACID
157
sulphuric acid, and deposited on the floors of the it is chambers, whence it is run off from time to time called " chamber-acid." Formerly, the nitric oxide and peroxide used to escape into the air and be lost, besides into
;
causing
a
nuisance
;
to
save
Gay-Lussac devised
it,
a
means of trapping it by passing the escaping gases up a a stream of concentrated tower which bears his name down this acid flows tower, moistening the coke sulphuric On coming into contact or flint with which it is filled. with the mixture of nitric oxide and peroxide, a salt of sulphuric acid is formed hydrogen nitrosyl sulphate, ;
-N=O
HO-SO,-O-N=O, the group having replaced This one of the hydrogen atoms of the sulphuric acid. compound dissolves in the excess of sulphuric acid it is conveyed by means of a special pump to the Glover tower, where it is mixed with water, and is decomposed, thus ;
:
2
HO-SO -O-NO + H O = 2HO-SO -OH = NO + 2
2
2
NO.,. Although this compound is formed by the action of concentrated sulphuric acid on a mixture of and NO.,, yet excess of water causes the action to proceed in this affords a good example of the the opposite sense action of mass. After the chamber acid has been evaporated in leaden vessels until a portion of the water is expelled, it is further concentrated in vessels of platinum, glass, or iron. The dilute acid is without action on lead, and the concentrated acid does not attack platinum or iron, although iron is at once dissolved by dilute acid. The heavy oily liquid
NO
;
remaining after evaporation still goes by its old name of " oil of vitrol." Its composition is not quite expressed by the formula H. SO 4 , however, for that substance is unstable, 2 and parts with a trace of sulphuric anhydride when heated, It can be leaving a trace of water in the oil of vitrol. made by dissolving the right amount of anhydride in the acid to combine with that water
;
the resulting acid melts
10.5 ; oil of vitrol has a much lower melting-point. The molecular weight of liquid sulphuric acid, determined
at
MODERN CHEMISTRY
158
its rise in a capillary tube, is very high, and appears to correspond to about 3oH 9 SO 4 ; on dilution it is no doubt considerably lowered, and in dilute solution it is mostly in the state of ions. When heated to about 250, sulphuric acid, as oil of vitrol is usually termed, begins to emit fumes of anhydride ; apparent ebullition takes place at about 350, and the acid
by
This is, however, really dissociation into over. anhydride and water ; for the density of the vapour is not, as might be expected, half the molecular weight, 98, but only And this agrees with 24.5, one quarter of that number. the theoretical density of a mixture in equal proportions of the vapours of the anhydride and water, for (40 + 9) / 2 = considerable rise of temperature takes place on 24.5. mixing sulphuric acid with water ; it is not improbable that the first anhydride of the true ortho-acid is formed ; the SO 4 .H 9 O, which may be compound of the formula 2 O=S=(OH) 4 , melts at 8. The point of maximum contraction of a mixture of sulphuric acid and water occurs distils
A
H
H
HO
the proportion corresponds to SO 4 this is ; 9 S(OH) ,, but it does not easily solidify. Water can be withdrawn from sulphuric acid by distilling it with
when
possibly
.
(
phosphorus pentoxide, when sulphuric anhydride and distils over.
is
formed
Oxidising Action of Sulphuric Acid. Sulphuric acid can behave as an oxidising agent, being itself reduced. This change is produced when it is heated with most other
Thus with carbon, C + 2H.,SO 4 = + 2SO 9 with sulphur, S + HJSO 4 = 3 SO 2 + with C); ? copper, mercury, iron, lead, silver, &c., a sulphate is formed, and sulphur dioxide is liberated this may be viewed as the
CO
elements.
H
+ H 2 O;
;
reducing action of hydrogen, at the high temperature reSO 4 = CuSO4 + 2H quired for the reaction, thus : Cu + 2
and
H
H
SO 4 +2H = 2H 2 O + SO
=
The
reduction
goes
and some sulphur is liberated, while copper sulphide O SO 4 formed: CuSO 4 + 8H = CuS + 4 S-f 4 2 0.
further, is
.
H
H
;
H
SELENIC AND TELLURIC ACIDS
159
Hydriodic, and to a are
oxidised
2H.,O
+ SO 2
less extent hydrobromic acid also, by sulphuric acid: H.7 SO4 + 2HI = I. + and alcohol and many other compounds of 7
;
carbon have a reducing action on sulphuric acid.
H
SeO 4 , is also a Selenic Acid, 2 syrupy liquid ; it can be produced by direct oxidation of selenium by chlorine water, but on concentration the resulting hydrochloric acid reduces the selenic acid to selenious acid, as hydriodic acid reduces sulphuric acid. It is best prepared by addition of copper carbonate to the mixture of selenic and hydrochloric acids obtained in that way ; selenate and chloride of copper are formed ; the Selenic Acid.
colourless
mixture
evaporated to dryness, and the copper chloride is out with alcohol, leaving the insoluble selenate The selenate is dissolved in water, and on treat-
is
dissolved
behind.
ment with sulphuretted hydrogen, copper sulphide is prethe selenic acid is cipitated, and removed by filtration ;
then concentrated ; if it contains a trace of water, it is a heavy liquid ; but if quite anhydrous, it forms a solid, melting at 58. Telluric acid is prepared from its Telluric Acid. barium salt suspended in water, with the requisite amount
of sulphuric acid ; the barium salt is produced by heating tellurium with barium nitrate. On evaporation, the hydrate, H.,TeO 4 .2H 2 O, deposits in white crystals.
The sul^Sulphate, Selenates, and Tellu rates. phates, selenates, and tellurates of barium are nearly insoluble in water ; those of strontium and lead are very sparingly soluble, and those of calcium are still sparingly soluble,
though more easily soluble than the salts previously All these salts, therefore, are most conve-
mentioned.
niently prepared by selenate, or tellurate
addition of a soluble
the to
sulphate, soluble salt of calcium, stronNa thus : CaCl .Aq 4 .Aq a
= SO + tium, barium, or lead, CaS0 4 .2H 9 + 2NaCl.Aq Pb(NO 3 ).,.Aq + K 2 SO 4 Aq = PbSO 4 + 2KNO 3 .Aq. These salts are still less soluble J
in alcohol
;
than in water, hence addition of alcohol to their
MODERN CHEMISTRY
160
While barium sulphate is not attacked by boiling hydrochloric acid, barium selenate evolves chlorine, and is changed to barium chloride solutions produces a turbidity.
and selenious acid, thus BaSeO 4 + 4HC1. Aq = BaCL,. Aq + 2 SeO 3 .Aq + Cl 2 + 2 O. All other sulphates are soluble in water, and can therefore be prepared by one of the usual methods, such as treatment of the oxide, carbonate, or metal with the acid. :
H
H
Dilute sulphuric acid dissolves
aluminium, chromium, cobalt
other metals resist
;
magnesium, zinc, cadmium, manganese, nickel, and
iron, its
attack, because their electro-
than that of hydrogen. The order is Cs, Na, Li, Ba, Sr, Ca, Mg, Al, Mn, Zn, Cd, Cr,
affinity is less
Rb, K,
:
H:
Fe, Co, Ni, Pb:
All Cu, Hg, Ag, Pt &c., Au. of hydrogen in the table are attacked, because they receive their ionic charge from the hydrogen
the metals to the
left
of the dilute acid: the zinc
is
Zn + H 2 SO 4 .Aq = ZnS6 4 .Aq + H 2
ionised, receiving
which escapes
in
its
;
charge from the hydrogen,
the molecular condition.
But
this trans-
ference of charge appears to require the contact of
some
metal with lower electro-affinity than that of hydrogen, for in fact, the pure zinc is not attacked by pure dilute acid It is arrangement must be analogous to that of a battery. a possible that this is due to the protection of the zinc by ;
in other words, to polarisaof condensed hydrogen contact with another metal affords a means of escape of the charge from the hydrogen, which is evolved, not from the surface of the zinc, but from the surface of the
film tion
;
less electro-positive metal.
With concentrated acid, these metals, as before remarked, are dissolved as sulphates, with evolution of sulphur dioxide.
The
form an important group of salts. Among Sodium sulphate, Na 2 SO 4 .ioH 2 O, " Glauber's salt," contained in sea-water and in many SO 4 and (NH 4 ).,SO 4 hard rhombic mineral springs; 2 obtained the double salts, NaHSO 4 , ami 4 prisms sulphates
the best
known
are:
K
;
,
,
KHSO
,
THE SULPHATES by mixture
;
when
161
heated, these salts lose water and are
HO K
KHSO
= 9 + 2S 7 2 converted into pyrosulphates 4 CaSO 4 occurs native, as anhydrite, and CaSO 4 .2H 2 O, as :
gypsum and loses
its
O
.
alabaster. Gypsum, when gently heated, " is then known as "plaster of Paris ; takes to a paste with water, combination place
water, and
on mixing it " sets " and in this ; slowly, and the plaster way casts may be taken. SrSO 4 is found native as celestine BaSO 4 , as ;
heavy-spar or barytes. from containing barium
It
is
the
commonest mineral
it barium salts are prepared, by with ground coke, which reduces it to the sulBaSO 4 + 4C = 4 + BaS. The barium sulphide ;
heating
phide is
:
it
CO
then dissolved in the appropriate acid, and the required
is made. Precipitated barium sulphate is known as " owing to its low price, it is much permanent white used as a paint, although its covering power is small. MgSO 4 .7H 2 O, ZnSO 4 .7H 2 O, and CdSO 4 .yH 2 O, as well as FeSO 4 .yH 2 O, MnSO 4 .yH 2 O, and the correspond" ing cobalt and nickel salts, are isomorphous," that is, they in the same form rhombic Magnesium prisms. crystallise " sulphate, or Epsom salts," is present in sea- water and
salt
"
;
in
many mineral waters it also occurs in the salt deposits Germany, and is termed kieserite. It used as a purgative. Zinc sulphate is known as "white ;
at Stassfurth, in S. is
vitriol,"
"
and ferrous sulphate
as
A
"green vitriol"
large number of double copperas." .K 2 SO 4 .6H 2 formulas of which 4
MgSO
O
may
or
of the
salts exists,
serve as a
and they are ionised in solution into the same ions as the simple salts would furnish thus, + + + the ions of the salt mentioned above are Mg, 2K, and 2SO 4 SiF 6 , of They differ in this respect from such salts as 2 + which the ions are 2K and SiF g The alums form a similar series of double salts, in which monad metals, such as sodium, potassium, and ammonium, and triad metals, aluminium, chromium, iron, manganese and others, are combined together as sulphates with water of crystallisatype
;
they are
all
soluble,
;
.
K
.
MODERN CHEMISTRY
162
H
K
SO 4 .Al 2 (SO 4 ) 3 .2 4 2 O,orKAl(SOJ.,.i2H.2 O. 2 molecular weight of the compound is unknown hence, as usual, the simpler formula is preferable. These compounds are named from their analogy with the original " alum," of which the formula is given above ; they all crystallise in regular octahedra, and, like all true isomor-
tion:
The
;
phous
salts,
they are able to crystallise together
a crystal of in a solution of
KA1(SO 4
form
a
" Alum
(NH
dark-red
"
finds
12H 2 O
so that if
;
placed, for example, .i2H 2 O, the latter will 4 ) 2 Cr(SO 4 ) 2 .
)
on
layer
use as
a
the
is
surface
mordant
;
of
when
the
former.
textile fabrics
its solution, the fibre becomes incrusted with of aluminium hydroxide, and when subsequently dyed the colouring matter is retained in combination with the alumina and with the fibre, so that it cannot be removed This phenomenon depends on the fact that by washing. aluminium sulphate is partially hydrolysed by water into A1(OH) 3 and 3H 2 SO 4 ;" the adhesion of the alumina to the fibre is attributed to adsorption," a term applied to the adhesion of gases, liquids, or of substances in solution, solution of alum also gives to the surface of solids. coloured precipitates with many dye-stuffs, which are known as "lakes." Selenic acid also yields alums. Bismuth sulphate, Bi 2 (SO 4 ) 3 , obtained by evaporating a solution of bismuth oxide, Bi 9 g , in sulphuric acid, forms acicular crystals, which, on addition of water, like all other bismuth salts, yield a basic salt, in which the group O=Bi-, bismuthyl, plays the part of a monad metal ; hence the it is an formula of the basic sulphate is (O=Bi) 9 SO 4
are boiled in a
layer
A
O
;
insoluble powder.
Copper sulphate,
or
" blue
vitriol,"
CuSO 4 .5H 2 O,
forms blue soluble crystals; silver, mercurous, and mercuric sulphates, Ag 2 SO 4 , Hg 9 SO 4 and HgSO 4 , are sparingly soluble, white crystalline powders. ,
As
the ion
SO 4
is
colourless, all these salts possess the
colour of the metallic ion which they contain
++
;
thus,
Fe
SALTS OF RADICALS ++ is
Mn
green,
pink,
163
++ +++ +++ Cr green, Fe yellow, Ni
++ green,
Co
++ red,
Cu
blue,
and the others colourless.
Sulphates of the alkali- and alkaline-earth metals are stable at all temperatures lower than that of the electric arc ; all other sulphates decompose, the primary product being the oxide of the metal and sulphuric anhydride ; the latter,
but
however, being unstable at a red-heat, decomposes partly This decomposition into sulphur dioxide and free oxygen. " Nordhausen is made use of in the sulphupreparation of ric acid," a fuming liquid, consisting chiefly of 9 S.7 O 7 ; it is made by distilling partially dried ferrous sulphate from
H
fireclay
retorts:
2FeSO 4 = Fe 2 O 3 + SO 2 + SO 3
the
;
produced by the union of the anhy2SO g + 2 O = 2 S 2 (X. The iron oxide has a fine red colour, and is sold as a paint under the name " Venetian red." Salts of Alkyl Radicals. Salts of the alkyl radipyrosulphuric acid dride with water:
is
H
H
cals are as a rule volatile ; they are produced by distilling the alcohols with the respective acid. Ethyl nitrite, for
example, is formed by distilling sodium nitrite, and sulphuric acid :
a
mixture of alcohol,
NaNO 2 + tLSO,. Aq +
C 2 H 5 OH = C 2 H 5 NO 2 + NaHSO 4 .Aq.
It
is
a
volatile
with a pleasant odour, which, when boiled with potash, is hydrolysed, with formation of sodium nitrite and = K-O-N=O.Aq 9 + ethyl alcohol: C 2 5 cannot be pre+ C,H 5 OH. The nitrate, C 2 5 2, pared from nitric acid and alcohol unless the presence of nitric peroxide is excluded for this purpose urea, its 9 ) 2 , is added in small proportion to the mixture presence prevents the oxidation of the alcohol, and brings = C2 5 about the normal action C 2 5 + 3 + g liquid,
H NO
KOH.Aq
H ONO ;
CO(NH
H
;
H OH HNO
O.
The
H NO
nitrate resembles the nitrite in properties.
On
mixing alcohol with sulphuric acid there is a considerable rise in temperature, and hydrogen ethyl sulphate is produced :
C 2 H 5 O H + HO-SO 2 -OH . HO-SO 2 -OC 2 H5 + H 2 O. A" considerable excess of
sulphuric acid must be present in
MODERN CHEMISTRY
i6 4
ensure the nearly complete conversion of tht To remove this excess, calciur alcohol into the ethyl salt. carbonate is added, which forms sulphate of calcium ai
order to
H
SO
a double sulphate of ethyl and calcium, Ca(C 2 4)2 , 5 the former is nearly insoluble in water, while the latter is
readily soluble ; from the calcium salt the acid may be pr< duced by addition of the theoretical amount of sulphuric
On
acid.
it is a syrupy liquid ; it decomposes into ethylene, sulphur dioxide, carbon mon-
evaporation
when heated
As seen by the formula of the oxide, and carbon dioxide. The potassium calcium salt, the acid is a monobasic one. the salts salt, for example, has the formula K(C 9 )SO 5 4 ;
H
are
Similar acids are formed from other alkyl
all soluble.
&c.
radicals, such as methyl, amyl,
ThiosuIptiateS' be
to
other acids of sulphur remain these is thiosulphuric acid,
Among
noticed.
HSO
Some
of which the sodium salt is produced by digesting together sodium sulphite with sulphur, just as, with oxygen, In the latter case it may be sodium sulphate is formed. 2
2
3,
supposed that the atom of oxygen inserts itself between the sodium atom and the sulphur atom with which it is in com-
o
li
I!
Na-Q-S-Na + O = Na-Q-S-Q-Na
thus:
bination,
o
;
I!
II
O
O
o
o Na-O-S-Na +
S
= Na-O-S-S-Na
"
;
hence the name
1
li
"
thio
"
oxygen
I
O
O
" thion," or sulphur, replacing the sulphate, the The sodium salt forms large of sulphuric acid.
O
O
the ; transparent crystals of the formula Na 2 S 2 3 .5H 2 salt is sparingly soluble, and forms a crystalline
barium
precipitate on adding a solution of the sodium salt to one of barium chloride the lead salt is insoluble, and the silver salt is a white precipitate, which rapidly turns dark on ;
IODOMETRY
165
application of heat, being converted into
silver
Ag 2 S 2 O 3 + H 2 O.Aq = Ag 2 S + H 2 SO 4 .Aq.
sulphide
On
:
acidify-
ing any one of the soluble salts, the acid is momentarily liberated ; but it immediately decomposes into sulphurous
H
H
= 2 3 .Aq + S, the latter S acid and sulphur, 3 .Aq 2 2 The sodium salt, when a solurendering the liquid milky. tion of iodine in one of potassium iodide is added to it,
O
undergoes the reaction
S 4 O 6 Aq.
+ Na
.
of sodium.
:
2Na 2 S 2 O g .Aq +
The
salt
formed
is
I
2
.Aq = aNal.Aq
named
tetrathionate
It will be considered shortly.
lodometry.
A
sodium thiosulphate conto a litre with water, reacts
solution of
248 grams, made up
taining
SO
quantitatively with one containing 127 grams of iodine per the colour of the iodine disappears, and the vanishing ;
litre
of the last trace of iodine can be ascertained by the addition of some starch paste, which gives a blue colour so long as any free iodine remains unconverted into ions ; such a solution is commonly used in estimating iodine, or in determining the quantity present in solution of any substance which has the property of liberating iodine from acidified iodide, i.e. from hydriodic acid, such as free chlorine, a hypochlorite, or, indeed,
any oxidising agent. sodium thiosu)phate with its ethyl iodide, sodium ethyl thiosulphate is formed
On
boiling together solutions of
;
O I
formula
is
Na~ O~ S~ S~ C 2 H 5
when mixed with
for,
,
6 barium chloride, the barium salt, which is unstable, decomposes into barium dithionate and ethyl disulphide, thus :
/O-SO -S(C Ba/ \O-S0 -S(C 2
H,) 2
This decomposition
H
yO-Spa
= Ba/
renders
two
+
I
\O-SO
5)
S(C H.)
probable
suppositions
O. that
thio-sulphuric
acid
has
the
formula
.
I
S(C 2 H 5 )
2
/SH
/S\
O^ \OH
:
MODERN CHEMISTRY
166
/OH
S. and not
^S\
o^ NDH
>
and that dithionic acid
is
constitu-
O S-OH 2
tionally represented
by
I
0,S-OH Hydrosulphites. sometimes
called
"
Hydrosulphurous acid,
HSO 2
4
hyposulphurous acid," is produced as zinc salt by the action of metallic zinc on sulphurous acid. The liquid turns brown, and possesses great reducing The sodium salt, which is better known, is propower. duced by digesting zinc turnings with a concentrated solution of hydrogen sodium sulphite: Zn + 4HNaSO .Aq = 3
Na 2 Zn(SO 3 ) 2 + Na 2 S 2 O 4 .Aq + 2H 2 O
;
the sodium zinc
sulphite crystallises out on addition of alcohol, leaving the cooling the solution, slenhydrosulphite in solution.
On
der crystals of the hydrosulphite separate. absorbs free oxygen so rapidly that it turns
The solution warm it is ;
used as a reducing agent in indigo-dyeing indigo-blue is converted by the hydrogen of water (of which the oxygen ;
enters
into
it
into
ing
combination with the hydrosulphite, convertsulphite) into a colourless substance, termed
this body being soluble, penetrates the fibre indigo-white of fabrics dipped into the solution, and on exposure to air, indigo-blue, with its usual colour, is deposited as an insoluble precipitate in the cloth. By help of sodium hydrosulphite, too, a ferrous salt may be deprived of ferric so completely that it gives a nearly white precipitate with alkalies ; the usual colour of the impure ferrous hydroxide ;
is
a dirty green.
Thionates.
Manganese dithionate
is
produced by
passing a current of sulphur dioxide through freshly prepared manganese dioxide suspended in water, made by The equaboiling potassium permanganate with alcohol. tion
MnO
2
.nH 2 O + 2SO 2 .Aq =
MnS 2 O 6 .Aq represents
the
On addition of barium hydroxide to the manchange. ganese salt, manganous hydroxide is thrown down, and
THIONATES barium dithionate may be prepared by sulphuric
acid
;
167
From
the acid the addition of the requisite amount of and the other salts, by addition of the is left
in solution.
it,
The acid, concentrated by evaporaappropriate sulphate. tion at a low temperature, is a sour, syrupy liquid ; when heated, it decomposes into sulphur dioxide and sulphuric acid.
H
S O 6 is also known it is a still Trithionic acid, 2 3 more unstable liquid. Tetrathionate of sodium, as already remarked, is produced by addition of a solution of iodine to a thiosulphate ,
;
;
The acid forms precipitated on addition of alcohol. The colourless a with strong acid taste. solution, method of its formation gives a clue to its constitution :
it is
NaO-S(0 2 )-S-Na
NaO-S(O 2 )-S-Na
Nal
I
=
+
NaO-S(O 2 )-S +
I
Nal
I
H O
I
NaO-S(O 2 )-S
S 6 , is produced by passing a Pentathionic acid, 2 5 current of hydrogen sulphide through a dilute solution of sulS phurous acid, along with tri- and tetrathionic acids :
+ 5SO 2 .Aq. = H 2 S 5 O 6 .Aq + 4 H 2 O +
5H
the equation Excess of hydrogen sulphide, passed for a usually given. = 9 S + SO 9 .Aq long time, results in the reaction
5S
is
2H
2H 2 O.Aq + 3S.
The
and pentathionates, when heated, yield a sulphate, sulphur dioxide, and free tri-,
tetra-,
sulphur.
Of recent years, a conof acids more highly oxidised than any of those already mentioned has been prepared. It has long been known that on addition of hydrogen dioxide to a solution of potassium bichromate acidified with Highly Oxidised Acids.
siderable
number of
salts
sulphuric acid, a bright blue colour is produced, and that this coloured substance can be extracted by ether from its
aqueous identified
solution. as
The compound
perchromic
acid,
has
recently
CrO 4 (OH);
been on
for,
adding to the cooled blue solution a solution of ammonia is ether, a violet precipitate of CrO 4 (O 4 ).H
in
NH
O
1
MODERN CHEMISTRY
68
thrown down
and if an etherial solution of potassium hydroxide be added, the potassium salt of similar formula is
;
These bodies are explosive. Persulphates of potassium and ammonium are produced
precipitated.
a current of electricity through concentrated solutions of the sulphates in water. The persulphate is
by passing
and deposits in white crystals. The = monad metal). S appears to be 2 2 g The acid has bleaching powers, and gradually decomposes into sulphuric acid and ozone. sparingly soluble,
formula
M
O
(M
NaBO 3 ,4H 2 O, is may be produced by cooling
Perborate of sodium, pared,
or
it
similarly prea solution of
borax to which some caustic soda and hydrogen peroxide have been added. It, too, is a sparingly soluble salt, possessing bleaching properties.
CO
iiR 9 O, is similarly Percarbonate of sodium, Na 2 4 prepared by addition of alcohol to a solution of sodium carbonate, to which a solution of hydrogen peroxide has It is a white, been added. extremely unstable compound, possessing, like the other similar salts, great oxidising power.
.
CHAPTER IX The Nitrides and Phosphides, Arsenides and Antimonides Complex Amines and their Salts Acid Amides The Cyanides and the Double Cyanides. Analogy between Oxides and Nitrides. Nitrogen and phosphorus are best characterised by the compounds in which they act as triads. For just as an oxide or hydroxide may, as was customary during the era of the theory of "types," be regarded as water in which the atoms of hydrogen are more or less completely replaced by atoms of a metal so from analogy it is to be inferred that compounds should be preparable which should be similarly related to ammonia and to hydrogen phosphide; The ;
following clear
graphic
formulas
will
render
the
conception
:
H-O-H H-NH H-O-H
-*.
->
2
j
Na-O-Na
->
Na-N=Na,
->
Ca<
;
;
->
->
Ca<
\NH 169"
Ca=0; ,N=Ca
/NH,
2 )
I
->
,0-H
)
H-O-H f H-NH
H-NH
Na-O-H Na-NH 2
Ca< \N=Ca
;
MODERN CHEMISTRY
H-O-H) H-O-H V H-O-H
H-NH
/OH \OH
-*
Cr/
-*
V
-
Crf X
>O.
OH NH /X
/NH NH
)
H-NH;
x/
->
Cr^-OH
-*
Cr
Cr/
Cr=N.
->
H-NH
But although most elements combine with oxygen directly, there are only a few which burn in nitrogen. Among these are lithium, calcium, and magnesium ; boron and titanium The nitrides of the other also possess this property.
elements
are
practically
unknown.
These
nitrides
are
with violence at the ordinary temperature ; the two last, when heated in a current of steam. The products are the hydroxide of the metal and ammonia ; or with boron and titanium, owing to the high temperature of action, the oxide, thus g 2
attacked by water
the three
;
first
:
+ 3 H 2 O.Aq= 3 Mg(OH) 2 + 2 NH 3 .Aq. Nitrides.
Lithium nitride, Li 3 N, formed
is
Mg N
a dark-coloured
the ordinary temperature on expos, is a ing metallic lithium to the air. Calcium nitride, Ca 3 greyish-yellow substance ; and magnesium nitride, 2, 3
substance
;
it is
at
N
>7
Mg N
Combination takes place readily with a yellow powder. great evolution of heat when a mixture of dry lime with
magnesium powder nitrogen
;
this
is
heated to dull redness in a current of method of separating
affords a convenient
nitrogen from the indifferent gases of the atmosphere, and Boron nitride, preparing the latter in a state of purity. BN, is a white amorphous powder ; it can also be produced
by heating to redness a mixture of boron oxide with ammonium chloride, until excess of the chloride has volatilised. Hydrazoates. Besides these compounds, which may be regarded as the analogues of the oxides, a series of nitrides is known, which correspond in formula with
hydrazoic acid, pounds
is
HN
sodamine,
3
.
The
NaNH
2
starting-point for these
(see below).
com-
This compound
HYDRAZOATES
171
heated to 300 in a series of small flasks in a current of nitrous oxide, when the following reaction takes place : is
2NaNH 2 + N 2 O = NaN 3 + NaOH + NH 3
which takes place
is
and
reaction
NaNH + O/ 2
= ||
NaNH + H O = NaOH + NH 2
product of the reaction dilute sulphuric acid,
is
con-
M
N
ceived to occur in two stages:
+ H 2 0;
The change
.
more obvious when the
2
is
and
NaN<^ .
||
The
?
dissolved in water, acidified with
distilled
= HN 3 .Aq + NaHSO 4 Aq.
:
NaN g .Aq + H SO 4 Aq .
The
.
distillate,
which
is
a
dilute solution of hydrazoic acid, has a peculiar odour, and if its vapour be inhaled, fainting may result ; it is necessary
to take
precautions to distil
it
in
a
good draught.
The
may be prepared by neutralisation with the hydroxides or carbonates of the metals. The ions, -N s , are colourless, and the salts of colourless ions are themselves white. Those of lithium, solution has an acid reaction
;
salts
sodium, potassium, magnesium, calcium, strontium, barium, and zinc are crystalline their formulae are M'N g and M"(N 3 ) 2 respectively. Silver hydrazoate, AgN 3 , closely resembles the chloride in appearance and in in;
it is, however, dangerously easy to explode, and should be prepared dry only in minute quantity, and treated with the utmost precaution. Titration with a
solubility
;
deci-normal solution of silver nitrate affords a convenient method of determining the strength of a solution of hydrazoic acid, or of analysing the hydrazoates ; it is easy to recognise the point when all hydrazoic acid has been
removed
as the insoluble silver salt.
Amines.
Substituted ammonia, in
which one atom of
replaced by an element, is the analogue of the Such bodies are termed amines or amides. hydroxides. is Sodamine, easily prepared by passing a current 2,
hydrogen
is
NaNH
of ammonia, dried by passing it through a tower filled with soda-lime, through an iron U-tube containing sodium, and heated to about 300. The gas is rapidly absorbed, while
MODERN CHEMISTRY
172
When
evolved
is
hydrogen
2NH +
:
2Na = aNaNH., +
3
the sodium has been
H
.
converted into sodamine, the tube is emptied by pouring out its contents. Sodamine is a white brittle substance, with crystalline fracture, not all
unlike caustic soda, melting at about 100. So long as it is kept dry it is quite permanent, but with moisture it at once reacts,
forming ammonia and caustic soda
= NaOH + NH 3
NaNH., +
:
HOH
compounds can be made with lithium, potassium, rubidium, and probably caesium. The corresponding compound of zinc, Zn(NH 2 ) 2 is a white powder, insoluble in ether, formed along with ethane or methane by the action of ammonia on zinc methide or Similar
.
,
ethide
Zn(CH 3 + 2NH 3 = Zn(NH 2 2 + 2CH 4 An attempt to produce the amine
:
.
)
).,
Guanidine. carbon,
C(NH
a
as
body
C(OC 9 H
r
)
by
2 ) 4,
carbon
or
tetrachloride
according
4,
action of
the to
the
of
ammonia on such orthoformate,
ethyl
equations
CC1 4 + 4NH 3
= C(NH 2 4 + 4HC1, or C(OC 2 H 5 ) 4 + 4 NH 3 = C(NH 2 ) 4 + 4HOC 2 H 5 fails, owing to loss of ammonia. For just )
,
orthocarbonic
C(OH)
loses water, yielding acid, 4, ordinary carbonic acid, so carbon tetramine loses ammonia ; the product is named guanidine, and has the formula as
HN = C(NH,)
like
2
;
Guanidine
seen.
ammonia,
On dine,
its
analogy with
O=C(OH)
2
is
a white crystalline substance, unites with acids to form salts. is
easily
which,
comparing the formulae of carbonic acid and guaniit
is
evident
that
several
should be capable of existence.
C(OH) 2 (0 = C(NH,) 2 (4)
intermediate
The
HN = C(OH) (2)
HN = C/ 15)
2
series
is
compounds
:
=C
^
(3)
HN = C(NH,).,. (6)
CARBAMATES Of
known
these, the best
which
ammonium
are the
salt
of (3),
termed carbamic acid, and (4), the important
is
compound urea
or carbamide.
Ammonium
Carbamates.
name of "
the familiar
ammonia
and
soluble in water
4
carbamate, known by is formed by mixing
smelling salts/'
dioxide
carbon
H N CO ONH when
173
CO +,2NH 3 =
gases:
2
a white crystalline compound, Its solution, smelling of ammonia. It
.
and
is
compound of which the formula above ; but after standing, it is converted by This has absorption of water into ammonium carbonate. been ascertained by treating the freshly prepared solution with sodium hypochlorite, when only half the nitrogen which the substance contains is evolved
is
fresh, contains the
given
:
H N-CO-ONH Aq + 3 NaOCl.Aq = 2 H N-CO-OH.Aq + 3 H O + 3 NaCl + N 2
4
2
.
2
2
on the other hand, with a hypobromite, is
evolved
all
2
;
the nitrogen
:
H N-CO-ONH 2
Now, ammonium mixed with
4
.Aq + sNaOBr. Aq = CO 2 +
salts
yield
up
their
a solution of a hypochlorite
when
nitrogen
hence
concluded that the compound contained in a fresh solution is ammonium carbamate. But on standing, the solution changes, and after some time it yields all its nitrogen on treatment with hypochlorite ; hence the assumption of the elements of water and a change into ammonium car= bonate may be inferred: 2 4 .Aq + H,O
H N O CO ONH 4
conceivably
possess
and
be that
it
may
attack.
This
last
4
.
is
is
H N-CO-ONH But ammonium carbamate may formula HO C(NH) ONH NH group which the 4
;
resists
is
supposition
of urea with hypochlorite nitrogen
it
Aq.
the it
;
;
is
for
confirmed by the behaviour with it, too, only half the
evolved.
Carbamide.
Urea
or
carbamide,
to
which the
for-
MODERN CHEMISTRY
174
mula O = C(NH 2 ) 2 is generally ascribed, is the form in which by far the largest part of the nitrogen is evolved which is consumed as food by animals. It may be directly prepared from urine by evaporation to one-third of its bulk, the sparingly and addition of nitric or of oxalic acid ;
soluble nitrate or oxalate
precipitated ; the salt is purified water, and is then mixed with
is
recrystallisation from caustic soda and evaporated
by
to
On
dryness.
treatment
with alcohol, the urea alone dissolves, and deposits in It is a white, easily crystals from a concentrated solution. It unites with acids, soluble substance, with a saline taste. salts ; but as the carbonyl group, CO, has the property of conferring acidity on neighbouring atoms of hydrogen, the basic qualities of only one of the two can display itself; hence the foramido-groups, 2,
forming
NH
mula of the hydrochloride is and not 2 ) .HC1, as might be expected. It is therefore 2 ) 2 .2HC1, a mono-acid base. Urea can also be produced from inorganic sources, and it was the discovery of its synthesis from potassium cyanide by Wohler in 1827 which caused the abandonment of the old view that compounds containing carbon, with the exception of its oxides, belonged to a special class, and could be produced only by the intervention of " life-power." Its Potassium cyanide is heated to production is as follows redness with lead oxide; + PbO = + Pb. The cyanate, KCNO, is next dissolved and mixed with a solution of ammonium sulphate, and the mixture is evapo-
CO(NH
CO(NH
:
KCN
KCNO
It may be supposed that potassium to dryness. sulphate and ammonium cyanate are first formed: 2 But the latter 2 4 +
rated
KCNO
+ (NH 4 ) 2 SO 4 = K SO
compound
is
isomeride, urea
unstable, :
(NHJCNO.
and
(NHJCNO
ment with alcohol,
undergoes
change
- O=C(NH 2
.
) 2
into
On
its
treat-
insoluble potassium sulphate remains undissolved, while the soluble urea crystallises from the alcohol on evaporation. Urea is also produced when carbonyl chloride or when ethyl carbonate is treated with aqueous
AMIDES OF PHOSPHORUS ammonia
HC1 2C
H a
in
O=CC1 +
:
0=C(OC
;
OH. 5
sealed
2
H
2NH - O=C(NHA,.HC1 + + 2 NH - 0=C(NH + 3
5)2
3
Lastly, carbamate of loses
tube,
175
2)2
.
ammonium, when heated
water with
of urea
formation
:
= 0=C(NH 2 ) 2 + H 2 0. When urea is heated, a body named
H N-CO-ONH 2
4
Biu ret. biuret is are here formed, with loss of one molecule of ammonia. reminded of the relation between an acid and an anhydroacid ; this is evident on inspection of the formulae :
We
H N-CO-NH 2
HO-SO -OH
2
2
Urea.
Sulphuric acid.
H N-CO-NH-CO-NH 2
HO-SO -O-SO -OH
2
2
Biuret.
2
Anhydrosulphuric
Amides of Acids
of Phosphorus.
acid.
Many com-
pounds analogous to urea are known, where the hydroxyl 9 groups of acids are replaced by amido-groups, By the action of ammonia gas on phosphorus oxychloride = ortho-phosphamide is formed O=PC1 3 + 2 The ammonium chloride formed by 9 ) 3 + 3HC1. the combination of the hydrochloric acid with excess of ammonia is removed by washing, and an insoluble white
NH
:
.
3HNH
O=P(NH
powder remains. When phosphamide is heated, ammonia is lost, and phosphoryl-amide-imide (the group =NH is termed the "imido-group"), HN=PO(NH 2 ), and at a higher temperature, N=P=O or phosphoryl nitride are
They are also white insoluble powders. By analogy with carbamic acid and urea, there should exist compounds in which both hydroxyl and the amido-group are present. Some such compounds are known. Thiophosphamic acid, S=P(NH 2 )(OH) 2 , is the product of the action of ammonia on thiophosphoryl chloride ; and phosphoric anhydride, when dry ammonia gas is passed over it, yields left.
O. phosphimic acid,
thus
:
P 9 O + 2NH* = r
^P
OH
MODERN CHEMISTRY
176
+ H 9 O.
It
^P OH,
is
analogous
and
forms
to
acid,
metaphosphoric salts.
crystalline
Pyrophos-
acids are also known. The addition of phosphoryl chloride to a cold saturated solution of ammonia in the formation of pyrophospho-diamic acid results
phamic
H NX /OH \(PO) O (POV H N/ X)H 2
2
HO X
phoric
acid,
heating
the
HO/
of this
(PO)/
9
;
and on
body, one hydroxyl group
replaces one amido-group, yielding
H NX >(PO) O HO/
analogous to pyrophos-
/OH X)H
O
>(PO)
solution
,
/OH (PO)/ \OH
pyrophosphamic .
acid,
Lastly, the action of
ammonia on phosphoric chloride gives a compound named phospham, HN=P N, a species of anhydride, but produced by loss of ammonia, not of water, from the unknown
compound
P(NH
2 )..
less well known if ammonia be passed over phosphorous chloride, a white mass is formed, which has not been separated from ammonium chloride, but which is supposed to possess the formula P(NH 2 ) 3 it may be named phosphorosamide. Amides of Sulphur Acids. Similarly, amido-
Analogues of phosphorous acid are
;
;
derivatives can be obtained
from sulphur trioxide.
The
ammonia on that compound yields ammonium N O (SO 9 ) 9 or, if less ammonia sulphamate, 4 be used, sulphamic acid, HO-(S0 2 )-NH 2 they are action of
H
NH
,
;
both crystalline, soluble compounds. The action of sulphur dioxide on ammonia is accompanied by the production of the analogous compounds, ammonium sulphurosamate and sulphurosamie acid, the latter of which has the formula 2
RO-(SO)-NH
.
COMPLEX AMINES
177
These compounds may be taken as instances of bodies analogous to acids, in which the hydroxyl is replaced by the amido-group. They are, as a rule, stable in presence of water, and they do not generally unite with acids, the acid nature of the oxygen which they contain counteracting the basic nature of the amido-group. Many compounds are however known, in which the amido-group replaces
hydroxyl, and which, having no acidic oxygen present, are known only as salts in combination with acids. Some of these will now be described.
Calcium chloride, Salts of Complex Amines. exposed to a stream of ammonia gas, rapidly absorbs it, and forms the compound CaCl 2 .8NH g . It would appear that this compound is one of calcamine, Ca(NH 2 ) 2 with zHCl, with which six molecules of ammonia are associated in some manner resembling that in which water of crystalThus we have lisation is associated in salts containing it. CaCl 2 .6H 2 O and Ca(NH 3 ) 2 Cl 2 .6NH 3 has an analogous formula. Zinc and cadmium form similar compounds, and other salts may be obtained from the appropriate salts of the metals thus, by saturating zinc sulphate with ,
;
;
ammonia, the compound Zn(NH 3 ) SO 4 .H 9 O separates in crystals. Again, with aluminium, A1(NH 8 ) 3C1 3 has and dyad iron, manganese, and nickel been prepared Such bodies must yield somewhat similar compounds. be regarded as salts of ammonium, in which a metal has taken the place of one atom of hydrogen in each a dyad metal replacing two molecule of ammonium metals in two molecules of ammonium, a triad three, and so on. The state of such compounds in solution is probably that of "double salts," alluded to on pp. 10 and 161. While some of them are decomposed by water into ammonia and the salt of the metal, others resist that decomposition, and are ionised into complex groups, analogous to the platini;
;
the
chloride
or
probable
that
silicifluoride
the
group.
Thus, while
it
is
compound of ammonia with calcium
1
MODERN CHEMISTRY
78
chloride
solution
in
contains
ions
as
NH
Ca, Cl,
4,
ar
NH OH
OH,
and molecul together with non-ionised 4 the fact that zinc hydroxide, precipitated by additic of ammonium hydroxide to a solution of the chloride,
NH
3,
re-dissolved by further addition of ammonia, is doubtless to be explained by the formation of the complex ion which is soluble in water. But this does not g ) 2,
Zn(NH
exclude the presence of the usual ions, Zn, Cl,
NH
4,
and
OH,
which doubtless co-exist with those already mentioned. In some cases, the stability of the complex ions is much greater than in that mentioned, and of this some instances will be given.
Chromium hydroxide,when digested
Chromamines.
with excess of ammonia and ammonium chloride, forms a and on exposing it to air, a violet deep red solution powder separates, of the formula CrCl 3 .4NH 3 .H 9 O. This powder, heated to 100, loses its water of crystallisation, The and the residue has the formula CrCl 3 .4NH 3 ;
.
ammonia
not
is
reached.
expelled
until
would appear,
It
the temperature
200
is
therefore, that this compound the fourth molecule of ammonia
not Cr(NH 3 ) 3 .Cl 3 .NH 3 , being regarded as of the same nature as water of crystallisation ; it must rather be supposed that a complex ammonium is
group,
NH NH, q
is
compound would have
capable of existence
/NH
the formula
;
3
Cr\-NHo
\NH
3
whence the Cl
NHo
Cl.
'
Cl
chromium have been prepared, in which ammonia are associated with chromium salt. They find their explanation
Salts containing 3, 4, 5, 6,
and
7 molecules of
the original by a hypothesis like the one given. Cobaltatnines. Similar compounds are
known with adding a solution of ammonia to cobalt sulphate, the precipitate at first .formed (a basic sulphate)
triad cobalt.
On
AMINES
179
exposure to air causes the oxidation of the cobalt from dyad to triad, and a black powder is deposited. On careful addition of hydrochloric acid, keeping the mixture dissolves
;
cold, the colour of the
/NH
pound has the formula
to red
powder changes
Coe-NH
the
;
com-
Cl
3
NH
Q
C1.H O. and
Q '
is
\NH|-C1 analogous to the chromium compound mentioned above. Other salts of this base have been made ; they are termed If temperature be allowed to rise, roseo-cobaltamines.
during the addition of hydrochloric acid to the oxidised solution of cobalt sulphate in ammonia, an isomeric substance is produced, containing no water of crystallisation, and
Other salts are known they are having a purple colour. termed salts of purpureo-cobaltamine. It is possible to represent the formulae of such compounds as follows ;
:
Diamines: Cl-Co(NH ),C1,. Triamines Co(NH 3 ) s Cl 3 Tetramines: Cl-Co(NH 3 Pentamines 9 -Co(NH- 3
NH
Hexamines:
Cl 3
.
:
:
NH
-NH
Co(NH 3 -NH 3
)
3
3)
Cl,. 3
);CL.
.
Other Amines. Many compounds of copper, mercury, silver, gold, and the metals of the platinum group are known, which admit of representation in a similar manner. They differ, however, inasmuch as the metal must be considered to have replaced more than one atom of Thus we have hydrogen in one molecule of ammonium. Cu' 2 9 Cl, di-cuprosammonium chloride, a black powder produced by the action of ammonia gas on warmed :
=NH
cuprous chloride Cu' 3 C1,
NH
:
cuprosammonium
absorbent for
chloride, formed by
ammonia carbon monoxide and for
dissolving cuprous chloride in
;
it is
a
well-known
acetylene.
Cu"=(NH 3 ) 2 Cl 2 cuprammonium chloride, and cuprisulphate, Cu"=(NH 3 -NH 3 2 SO 4 the ,
diammonium
former a green substance, the
)
latter a
,
deep blue compound
;
MODERN CHEMISTRY
i8o
both produced by the action of ammonia on the respective The formation of the latter is a well-known cupric salt. test for
With
copper. silver
there
are
:
a
Argentamine,
AgNH
plosive powder, probably of the formula by adding ammonia to silver hydroxide
compounds of formulas dissolving
the respective
Ag(NH
silver
salts
3
in
;
ex-
produced and numerous
produced by ammonia. With
)Cl,
Auric chloride, digested with ammonia, yields fulminating gold," an explosive black substance, which is
gold
"
like
black 9,
:
a mixture of
HN= AuCl
and
HN=Au-NH
A familiar test for mercurous mercury
2
.
add ammonia, when the compound turns black. This is due to the formation of di-mercurosammonium chloride, or some similar compound, of the formula Hg' 2 where two 2 Cl, atoms of hydrogen in ammonium chloride are replaced by It has long been known, two atoms of monad mercury. too, that mercuric salts produce a white precipitate on treatment with ammonia. This is chiefly due to the formation of here, the presence chloro-mercuramine, Cl Hg" 2 is
to
=NH
NH
;
of electro-negative chlorine deprives the amido-group of basic properties. On boiling this compound with ammo-
nium chloride,
mercurammonium
chloride is produced: Cl 2 )2 With platinum, and the other members of that group, but their constitution can similar compounds are produced be inferred sufficiently from what has preceded. These compounds are derivatives of ammonia ; there are few similar compounds of phosphine one, however, is
Cl-Hg-NH 2 + NH 4 Cl - Hg(NH 3
.
;
;
produced when phosphoretted hydrogen is passed over And aluminium chloride; its formula is 3 .3A1C1 3
PH
.
through a solution of mercuric chloride, yields Hg 9 AsCl.HgCl 2 it is somewhat analogous to the black
arsine, passed
;
precipitate,
Hg 2 NH.HCl.
Phosphides, Arsenides, and Antimonides.
A
few compounds of phosphorus, arsenic, and antimony with metals have been made. They are generally obtained by
PHOSPHIDES, ETC.
between the heated metal and the element.
direct union
Thus,
if
xylene,
181
sodium and phosphorus be heated together under a hydrocarbon boiling about 130, a black com-
pound is formed, Na 3 P, from which excess of phosphorus can be dissolved out by treatment with carbon disulphide. Arsenide and antimonide of sodium are also obtained by The formulae of these heating the elements together. compounds are of the type AsNa 3 ; and with dilute acid, the corresponding hydride of phosphorus, arsenic or antimony is
A
AsNa 3 + 3HCl.Aq = evolved mixture of calcium phosphide, :
AsH g +
3NaCl.Aq.
Ca 3 P 9 with ,
calcium
produced on throwing phosphorus into a crucible containing red-hot lime ; on treatment with water, is
pyrophosphate
inflammable
spontaneously
spontaneous ignition
is
phosphine is evolved. due to its containing P 9 4 , a
H
The liquid,
very unstable compound. The phosphides, arsenides, and antimonides of the other metals are usually dark-coloured substances, with
more or
less
metallic
Some
lustre,
of them
and therefore conductors of occur
native for example, smaltine, CoAs 9 a common ore of cobalt, forming silverwhite crystals copper-nickel, NiAs, red lustrous crystals, and one of the chief nickel ores speiss, a deposit formed in the pots in which smaltine and copper-nickel are fused with potassium carbonate and silica, in the preparation of smalt, a blue glass containing cobalt ; its formula appears to be Ni 3 As 2 Mispickel, or arsenical pyrites, is a white lustrous substance, of the formula FeS As. Cyanides. The elements carbon and nitrogen form a very stable group, of which the compounds have been well Carbon and nitrogen do investigated, termed cyanogen. but if a mixture of finely divided carbon not unite directly with carbonate of potassium or sodium, or, better, of barium, be heated to about 1200 in a current of nitrogen, combination ensues, and a cyanide is formed, KCN, NaCN, or Ba(CN) 2 BaCO 8 + 4 C + 2 = Ba(CN) 2 + 3CO. Potassium cyanide is also produced when a mixture of animal electricity.
,
;
;
.
;
;
N
;
1
MODERN CHEMISTRY
82
refuse
(horns, hides, hair, dried entrails, &c., of animals)
with potassium carbonate and iron filings is heated. The nitrogen of the animal matter and the carbon unite with the On addition potassium of the carbonate, forming cyanide. of water, this cyanide reacts with salts of iron, forming a double cyanide of iron and potassium, termed " yellow prussiate of potash," or ferrocyanide of potassium, of the formula When this compound is heated to 4 Fe(CN) 6 dull redness, it fuses a black mixture or compound of iron and carbon remains, and melted potassium cyanide can be Potassium cyanide, KCN, is a poured out of the crucible. it Its very soluble salt crystallises well from alcohol. solution smells of hydrocyanic acid this is because it is
K
.
;
;
;
The acid, HCN, is so very weak hydrolysed by water. that the number of hydrogen ions present in its solution are comparable in number with those of ionised water ; hence the change:
The
H-OH + K-CN.Aq=HCN + KOH.Aq.
ionised portion of the hydrocyanic acid is as usual nonvolatile ; but the non-ionised portion has a vapour-pressure,
and can be detected by
"
its
Acid. Hydrocyanic " prussic
acid
is
smell (cf. p. 141).
so very
Inasmuch weak,
it
as is
hydrocyanic
or
displaced from its even carbonic acid
by the action of all other acids ; can expel it. It may therefore be prepared by distilling a cyanide (potassium cyanide or ferro-cyanide is generally The vapour comes off used) with dilute sulphuric acid. along with water ; to remove the water, if the anhydrous acid is required, the mixture of vapours may be passed through a tube charged with dry calcium chloride, which retains the water ; or by another method, mercuric cyanide may be decomposed by passing over it a current of dry sulphuretted hydrogen, the excess of which is removed by causing the gases to traverse a tube filled with lead carbonate ; the hydrocyanic acid must be condensed in a freezing-mixture, for it boils at 27. The solid compound melts at 1.5. All experiments with anhydrous or with concentrated hydrocysalts
ISOMERIC CYANIDES must be carried out
anic acid for
of
a
in
183
good draught-chamber,
the most poisonous substance known, and a breath vapour has been attended by fatal effects.
it is
its
The cyanides
are produced by addition of the oxides or Those of the alkalies hydroxides to hydrocyanic acid. and alkaline earths are white, soluble crystalline compounds ; those of lead, mercury, and silver closely resemble the chlorides. Mercuric cyanide, a sparingly soluble, white crystalline salt, is formed by dissolving mercuric oxide
hydrocyanic acid ; lead cyanide is also sparingly soluble, silver cyanide, produced by addition of potassium cyanide to a soluble silver salt, is an insoluble white precipitate, unin
and
from silver chloride in appearance. The cyanide of silver or of mercury, when heated, yields cyanogen, distinguishable
(CN) 2 smell,
,
a colourless gas, possessing the characteristic cyanide that of bitter almonds. Like
somewhat resembling
hydrocyanic acid, blue-purple
flame
is
it ;
very poisonous. is
it
soluble
fairly
burns with a water and in
It in
It condenses to a liquid which boils at - 20, and freezes at It is an endothermic substance, 34.4. being formed from its elements with an absorption of heat
alcohol.
- 65,700
of
calories.
/some He Cyanides.
The formula of hydrocyanic It is possible to acid can be represented in two ways. conceive either the carbon or the nitrogen to be united In the former case, the with the atom of hydrogen. formula
structural
is
H-C^N
;
in
the latter,
H
N=C.
no method of determining which of the two formulae is to be ascribed to the acid or to its simple salts ; but salts with alcohol radicals are known to which one or On distilling potassium other formula can be ascribed.
There
is
cyanide with potassium ethyl-sulphate, the following change takes place 4-
K SO 4
group for the*
is
.
:K-C=N + C H .KSO = CH -CH -C=N 2
Here
in direct
it is
5
known
4
3
2
that the carbon of the ethyl
union with the carbon of the cyanogen
first, when ethyl cyanide is exposed to action of nascent hydrogen (e.g. treated with tin and
two reasons
:
MODERN CHEMISTRY
i8 4
hydrochloric acid) hydrogen adds itself both to the carbon and to the nitrogen of the cyanide group, and propyl9 , is formed ; and second, on amine, 3 2 boiling ethyl cyanide with a solution of caustic potash in alcohol, an acid with three carbon atoms, propionic
CH CH CH NH formed:
is
acid,
CH -CH -C=N
> CH CH C/ 3
2
3
+ NH 3
2
+
KOH
+
H O=
dyad oxygen and monad
;
On the other hand, if potassoxyl replace triad nitrogen. I, be boiled in alcoholic solution ethyl iodide, g 2
CH CH
with
silver cyanide, the
= CH 3
changeis
CH -N=C + Agl.
:
CH CH 3
+ Ag N=C
I
2
Here the nitrogen
2
is
in direct
union with the carbon atom of the ethyl group this is known because on boiling the compound with dilute acid, hydrotakes place, thus: +2 2 = lysis 2 3 the remains + nitrogen 3 2 2 ;
HO
CH -CH -N=C H-CO-OH;
CH -CH -NH
union with the carbon. Hence it is concluded that while potassium cyanide must contain C =N, along with (for both compounds are formed by the first silver action), cyanide consists almost exclusively of Ag N=C. The name applied to the first compound, in
K
K~N=C
CH CH
CN,
3
seeing
that
it
is
ethyl cyanide, or, preferably, propionitrile, from propionic acid only in having
differs
nitrogen in place of
oxygen and hydroxyl
;
while the
turned ethyl isocyanide or ethyl carbamine, for carbon replacing hydrogen in ethylamine, 3 is
it
latter
contains
CH CH NH
"
9
.
Hydrocyanic acid may on the same grounds be termed
formonitrile," for, on standing with dilute acid, it is converted into formic acid by assumption of the elements and of water: + +2 2 = 3 ; " oxalonicyanogen, for the same reasons, may be named
H-C-N
C=N
trile": |
C=N
+ 4H9
H-CO~OH NH
HO
CO-OH
= |
CO-OH
Perro- and Ferricyanides.
+2NH
3
.
Some of
the double
cyanides are of importance, both commercially and from- a
FERROCYANIDES
185
chemical standpoint. Among them is a substance which already been mentioned, potassium ferrocyanide, This . compound forms large yellow 4 Fe(CN) 6
has
K
tabular
crystals
hence the iron, supposed to be derived and to have the formula
contains
it
;
name
ferro(us)cyanide.
from
a
tricyanogen
It
group,
ferrous
is
KC.
XN
il
CFeC
N
The
ions
of
this
Fe(CN) 6
group
solution
caused
;
K
N
are five, viz., -f.K, and the
salt
the
/C N/ll
fall
by the
complex
in freezing-point of an aqueous presence of a gram-molecule in
parts of water, and the conductivity of a similarly dilute aqueous solution indubitably indicate the presence of
100,000
five ions.
Moreover, the
characteristic of ions of
salt
shows none of the reactions
iron, such as precipitation as ammonium sulphide, precipitation as
dyad
sulphide on addition of The acid correhydroxide on addition of alkalies, &c. sponding to this salt, hydroferrocyanic acid, 4 Fe(CN) 6 , can be prepared by adding to a boiled solution of potassium ferrocyanide concentrated hydrochloric acid and a little it The zinc salt ether precipitates in white crystals. and the copper-potassium salt, K 2 CuFe(CN) 6 are inthe former is white, and the latter a slimy brownsoluble
H
;
,
;
red precipitate.
On passing a current of chlorine through a solution of potassium ferrocyanide, or on submitting it to the action of any oxidising agent, potassium ferri(c) cyanide is formed 2K 4 Fe(CN) 6 . Aq + Cl, = KC1 . Aq + 2K 3 Fe(CN) 6 . Aq. :
The new compound " "
contains ferric
iron,
hence
its
name
;
This omitted for the sake of euphony. salt crystallises in dark red prisms, and dissolves in water The acid, prepared from the lead with an orange colour. the
c
is
1
MODERN CHEMISTRY
86
which
salt,
is
sparingly
and
acid,
sulphuric
forms brownish needles.
Fe(CN) 6
by the action of
soluble,
evaporation
Here
to
crystallising
again the complex group
one of the complex ions
is
+
dilute
point,
in
solution along
it now carries only of four, as in the ferrocyanide. Similar instances are to be remarked in elements of two
with
3K
three
and
;
to be noticed that
is
it
electrons instead
valencies
and
;
the manganates and the permanganates,
in
the former of which have the dyad ion
MnO 4
,
while with
The iron salts of ferroit is monad, MnO 4 and ferricyanic acids are especially interesting, and some of them are of commercial importance. On adding a solution the latter
.
of ferrocyanide of potassium, boiled so as to expel dissolved oxygen, to a solution of iron wire in sulphurous acid, which is also free from dissolved oxygen, a white precipitate of potassium ferrous ferrocyanide results FeSCX.Aq + = 2 Fe"Fe"(CN) 6 + 2 S0 3 .Aq. If 4 Fe"(CN) 6; Aq these precautions to exclude oxygen are not taken, the :
K
K
K
precipitate is light blue in colour, and is a common test for This compound is also formed when ferroferrous iron.
cyanide of potassium
is
distilled
with dilute sulphuric acid,
2K 4 Fe"(CN) 6 .Aq + + K SO 4 .Aq. When
as in the preparation of prussic acid:
H
K
=
SO
3 3 2 2 Fe"Fe"(CN) 6 4 .Aq 2 boiled with dilute nitric acid, the white
verted
into
regarded
blue
a
as
either
ferric
potassium
KFe'"Fe"(CN)
. fi
by the addition of
K 4 Fe"(CN) + gKCl.Aq +
K a
;
ferrocyanide, KFe"Fe'"(CN) 6 , or This same compound is produced also a ferric salt to potassium ferrocyanide
:
.Aq + Fe'"Cl 3 .Aq = KFe'"Fe"(CN) 6 .Aq or
by adding
a ferrous salt to potassium ferri-
Fe"'(CN) 6 .Aq + Fe"Cl 2 .Aq = 2KCl.Aq When mixed with excess Fe" Fe'" (CN) 6 Aq. ferrous salt, it gives a blue precipitate named
cyanide
of
K
G
compound is concompound, which may be potassium ferrous ferricyanide or soluble
:
3
.
CYANIDES
187
"Turnbull's blue": 2KFe"Fe'"(CN) 6 .Aq + Fe"SO 4 .Aq = Fe" 3 Fe'" (CN) 1: and with excess of a ferric salt, "Prussian "blue ""is formed: 3KFe"Fe'"(CN) r Aq + ,
Fe"'Cl 3 .Aq
;
= Fe" 3 Fe"' 4 (CN) ls + 3KCl.Aq.
ferricyanide, with ferric iron, gives a
brown
These colours
contain ferric cyanide. for ferric or ferrous iron.
may
Potassium
solution,
which
are used as tests
Chromicyanides, manganicyanides, cobalticyanides, ruthenocyanides, and osmocyanides, are also known, similar in formulas to the ferro- and ferri-cyanides. On the other hand, nickel and platinum form double cyanides similar
in
The platinum
formula to K.,Pt(CN) 4 .
salts
are very beautiful, possessing the property of dichroism, i.e. of transmitting light different in colour from that which the ; moreover, only some of the facets of the have this property. Silver cyanide is soluble in a solution of potassium cyanide, also forming a double salt, of the formula
crystals reflect crystals
KAg(CN) 2
.
Here
the
troplating
+
(see
KAu(CN) 4.Aq, AuCl 3
it
is
and
the
produced
Ag(CN) 2
the
elec-
in
electrolytically
by
.
compound from
Potassium
10).
p.
K
are
ions
This salt finds two uses. First, which silver is best deposited
auricyanide, of
addition
auric
of potassium cyanide, is Second, the existence of the employed in gold-plating. soluble ion, Ag(CN) , furnishes a means of estimating the amount of hydrocyanic acid in a dilute solution such as is decinormal solution of used for medicinal purposes. silver nitrate, that is, one containing one-tenth of the molechloride,
,
to
a
solution
A
cular weight of the salt taken in grams, or 17 grams per will react with 13.02 grams of potassium cyanide,
litre,
with 5.4 grams double salt, thus:
or
of
hydrocyanic
AgNO 170
+
KAg(CN)
.Aq.
The
acid,
forming
= 3 .Aq + 2KCN.Aq
KNO
the
8 .Aq
130.2 solution of silver nitrate
from a measuring-tube or burette
until
a
faint
is
added of
trace
MODERN CHEMISTRY
i88
turbidity begins to appear
given
above has
2AgCN of
this
signifies that
itself,
has just begun. silver nitrate added
second
Every cubic centimeter, therecorresponds to the presence of
0.0054 grams of hydrocyanic acid Metallic gold
in solution.
soluble in a dilute solution of potassium
is
or sodium cyanide, the formed, thus :
4 KCN. Aq
The
the reaction
and that the
KAg(CN) 2 .Aq + AgNO 3 .Aq= KNO 3 .Aq +
reaction
fore,
;
completed
Au(CN) 3
complex group
being
+ Au = KAu(CN) 4 Aq + K. .
action of the
potassium on the water is to liberate But this hydrogen attacks the oxygen dissolved hydrogen. in the water, and is removed The process is by water. largely used in recovering gold from poor gold ores, or from the " slimes," or mud left after removing the bulk of the gold from the crushed ore, by amalgamating it with mercury. The addition of a solution of potassium cyanide to a solution of a cupric salt in ammonia, which, it will be remembered, contains the blue ions of the cupramine,
+
+
Cu(NH 3
) 9,
decolorises the solution.
formation of the double -
+
K
2
-
Cu(CN) 4 .Aq,
salt,
This
is
due to the
potassium cupricyanide,
the ions of which are colourless.
The
++ Cu, hence
copper is not present in the form of cupric ions, does not give the reactions characteristic of these ions. For example, it yields no precipitate with sulphuretted hydrogen ; and this affords a means of separating copper from cadmium, which is unaffected by addition of potassium cyanide. it
CHAPTER X Borides and Carbides cation
Alloys: their classifi-
The commoner Alloys.
Borides and Carbides. These compounds have been incidentally mentioned on p. 30 ; they have been investigated. almost exclusively by Moissan and his pupils. Borides. Calcium, strontium, and barium borides have been prepared by heating in an electric furnace a mixture of borate of the metal with aluminium filings and At the high temperature of the electric arc the carbon. carbon reduces the aluminium oxide and prevents its These
formation.
compounds
form
hard,
transparent
microscopic cubes, burning only when maintained at a red heat in oxygen, and attacked with difficulty by the
Their formulae are curious ; they are analogous halogens. to the very unstable hydrazoates, M'(N) 3 , being Ca(B 3 ) 2 ,
Sr(B 3 ) 2 and Ba(B 3 ) ,
a supposititious
H-N/
;
and
compound of
their existence
the formula
would point
H
/B B<^
||
to
like
. ||
\N Ferric boride, produced by heating together boron and in an electric furnace, consists of brilliant
wrought-iron
yellowish-grey crystals, burning brilliantly
when heated
in
The corresponding oxygen, and attacked by nitric acid. compounds of nickel and cobalt, prepared in the same 189
MODERN CHEMISTRY
190
manner, form brilliant NiB, and CoB.
Carbon boride,
prisms.
CB 6
,
forms
The
formulae are
lustrous
black
FeB,
crystals,
nearly as hard as diamond, on which facets can be cut by its use ; it is produced by heating a mixture of amorphous
boron and sugar-charcoal in the electric furnace. Carbides. Lithium carbide, Li 2 C 9 is ,
a
white
crystalline furnace a
produced by heating in the electric mixture of carbon with lithium carbonate its
formation
is
mass,
;
Li 2 CO 3
expressed by the equation:
Li 9 C 9 + 3CO.
+ 4.C =
It is decomposed at a temperature not higher than that at which it is formed ; hence the exposure to the high temperature of the electric furnace The analogous compounds of should be only a short one.
much
sodium and potassium do
not resist such a high temperathey must therefore be prepared by exposing the metal for several weeks to the action of acetylene under This process yields compounds of the formulas pressure. ture
;
NaHC
KHC
and when heated, they change, with 2 ; 2 evolution of acetylene, into the carbides Na C 2 and 9C 2. Like lithium carbide, they are white crystalline substances,
K
and with water acetylene
2NaOH + C 2 H
2
is
evolved:
Na 9 C 9 + 2H O =
.
Calcium carbide, CaC 9 , has attained great industrial importance owing to its serving as the source of acetylene, now largely used for illuminating purposes. It was made in an impure state in 1892 by Travers by heating together a mixture of calcium chloride, carbon, and sodium ; but
it is
furnace,
best produced by Moissan's process in the electric by heating a mixture of carbon and lime to the
very high temperature (about 3000) obtained in that manner. It forms blackish-grey, lustrous crystals, at once = C 2 2 + Ca(OH) 9 . attacked by water: CaC 2 + 2 Carbides of strontium and barium are made in a similar manner, and have properties analogous to those of the
HOH
calcium compound. Other carbides prepared
H
by Moissan
in a crystalline
CARBIDES
191
CeC , LaC , state by means of the electric furnace are ThC , which yield with water a mixture of acetylene, , :
YC
ethylene, methane, and hydrogen ; Al 4 C g , which is decomposed by water, yielding pure methane ; 3 C, yielding C g , the products from which methane and hydrogen ; and 2
Mn
U
and hydrogen. By heating the oxide of the respective metal with calcium carbide, the carbides Cr 8 C , Mo.2 C, TiC, and SiC have also been 2 C, The last of these has become known comprepared. are ethylene, methane,
W
mercially
under the
name "carborundum."
It
forms
when extremely hard, blackish-blue, hexagonal crystals It is prepared on a large scale by pure it is colourless. heating together in the electric furnace a mixture of carIt is used for grinding and bon (coke) and white sand. polishing metals and glass. Steel, as is well known, differs from iron by the presence of a certain amount of carbon, which induces the iron, ;
when
This appears cold, to persist in its allotropic state. due to a carbide of iron mixed with the excess of The compound has been found as a iron in the steel. meteoric mass ; it has been named cohenite, and has the formula Fe g C. On treating steel with dilute acetic acid, Its forthe same substance remains as a black powder. mula is similar to that of manganese carbide, Mn 3 C. Some silicides have also been prepared by SHicides. aid of the electric furnace by heating elements with silicon. to be
Cr 2 Si, Ni 9 Si, these are Fe 2 Si, lustrous prisms Co Si, Mn^Si, Cu Si, and Pt 2 Si, with similar properties. Magnesium silicide, Mg 9 Si, prepared by heating a mixture
Among
;
of powdered silica and magnesium dust to redness, is attacked by dilute acid, evolving a mixture of hydrogen and hydrogen silicide (see p. 38).
Alloys.
The word "alloy" was
originally applied to
mixtures of gold and silver with other metals ; it now mixture or compounds of metals with each signifies any other ; alloys of mercury are, however, termed " amal-
gams."
When
two
metals
are
melted
together,
they
192
MODERN CHEMISTRY
Some may be mixed in any always mix, more or less. desired proportion, such as lead and tin others are partially soluble in each other ; zinc, for example, dissolves 1.6 per cent, of lead, and lead 1.2 per cent, of zinc but on stirring up the metals together, there is always a layer at the top of the lighter alloy of zinc with lead, and below it the heavier alloy, consisting chiefly of lead. By raising the temperature the mutual solubility of the metals increases, and at a sufficiently high temperature it is probable ;
;
would mix completely. Classification. Alloys in general may be classified I under two heads definite compounds, in which the ( ) elements are present in atomic proportions; and (2) mixtures in which combination has not taken place. To these classes may be added a third mixtures of definite comthat they
:
pounds with one or other of the components of the alloy. As such mixtures are usually homogeneous, it is often a matter of great difficulty to identify the definite compounds. In many cases, too, it would appear that one of the metals in the alloy is present in an allotropic form ; for example, on treatment of one of the alloys of rhodium and zinc with dilute hydrochloric acid, after solution of the zinc, the rhodium is left in an allotropic form. The constitution of alloys can be deciphered by several One depends on measurement of the electroprocesses. motive force of a battery consisting of the alloy and a plate for instance, platinum of some resistant metal compared with that of a similar cell made with one of the conTo take a concrete example. stituents of the alloy. Suppose a cell were constructed of a plate of copper and a plate of platinum dipping in some appropriate liquid, a certain electromotive force would result. Imagine a plate
of tin riveted to the face of the copper plate, the electromotive force would now be that of the more electropositive If a plate of bronze be substituted, supposing metal, tin. it to contain free tin not in chemical combination with the copper, then the electromotive force will still be that of
I
ALLOYS
193
A
chemical compound of tin and against platinum. copper, however, would have a less electromotive force than free tin ; and as the tin in the alloy mentioned is
tin
dissolved away, the electromotive force will suddenly fall when the excess of tin has been dissolved, until it is equal to that of the chemical compound against platinum.
An
analysis of the
alloy at
this
position of the compound. a compound of the formula
The
stage will reveal the comIn this way the existence of
Cu g Sn was
detected.
second method of determining whether an alloy
contains a definite
compound is to compare the freezingThe presence of points of various alloys of the metals. a small amount of one metal in another in general lowers the freezing-point ; and the freezing-point is continuously lowered by successive additions, until the lowering reaches a
maximum.
The
mixture which has the lowest possible
The commelting-point is termed the "eutectic" alloy. position of this alloy does not necessarily coincide with that of a definite compound ; indeed, metals which form no compound with each other exhibit this phenomenon. If a
compound a
is
formed, however, the melting-point rises to continuous addition of the second metal,
maximum on
and that compound which has the highest melting-point Further addition of corresponds with a definite formula. the second metal causes a lowering of the freezing-point of the definite compound ; and this lowering increases on addition of the second metal, until a second eutectic alloy formed, one consisting of a mixture of the compound Further addition of the with excess of the second metal. second metal now causes the melting-point to rise, it may be to the melting-point of the second metal ; in that case only one compound of the two metals is capable of is
It may happen, however, that, after rising to a certain temperature, the temperature again falls on addition of more of the second metal ; in that case, the highest temperature reached corresponds to the existence of a
existence.
second compound
;
a similar change
may
even denote the
MODERN CHEMISTRY
194
By such means it is possible to deof definite compounds between any two ternary alloys, i.e. with alloys containing
existence of a third. tect the existence
metals.
With
three metals, although the phenomenon is more complicated, this method has led to the discovery of several definite
compounds. alloys have generally been prepared by melting the metals together, or by melting one of them and adding the other, some alloys have been produced by submitting mixtures of the metallic powders to enormous pressure. " Fusible Alloys." Among the eutectic alloys, some
While
" Wood's as " fusible alloys." alloy" conof two parts of tin, two of lead, seven or eight of bismuth, and one or two of cadmium; it melts at 66-ji'y an alloy melting at 60 (Lipowitz's) consists of tin four parts, lead eight parts, bismuth fifteen parts, and cadmium are
known
sists
three parts.
Among the few alloys of definite composition are: ZnPt, Zn 3 Hg, Cd 2 Tl, Al 3 Mn, Sn 4 Pt, Cu 3 Sn, and PtHg 2 Attempts have been made to separate the constituents of .
by passing a current of high potential through the melted alloy, with the expectation that electrolysis would take place ; but no sign of such separation could be detected the alloy conducts as a whole. alloys
;
The following alloys, among others, find practical use: Sodium amalgam, made by adding small pieces of sodium to mercury, warmed under a layer of heavy paraffin oil; it is liquid when it contains under 1.5 per cent, of sodium, and solid
if it
contains more.
It
is
used as a
source of nascent hydrogen, for it is slowly attacked by On adding this water, and more rapidly by dilute acids. alloy to a concentrated solution of ammonium chloride, a
the amalgam very remarkable phenomenon takes place swells up enormously while retaining its metallic appearance ; the product is soft and of buttery consistency ; it may consist of ammonium amalgam, and may contain the ;
complex group
NH
4,
or,
more probably,
(NH 4
.
) 2
On
ALLOYS standing,
it
rapidly decomposes
into
195
mercury, ammonia,
and hydrogen.
The
addition of a
little
magnesium
to
melting-point considerably, and renders malleable. similar addition of a little its
A
iron also improves the qualities of the iron. is
called
"
" Mitis
nickel lowers it ductile and
aluminium
The
to
product
steel." "
Galvanised iron
is produced by passing clean sheets of iron through molten zinc. Alloying takes place on the Such plates, in a corrugated form, surface of the iron. are largely used for roofing buildings. As zinc is a more electropositive metal than iron, the iron is thereby protected from rusting. Iron is similarly coated with tin ;
but in this case, the iron, if exposed, is prone to rust, for iron is more electropositive than tin, and is attacked by
more readily than the tin. Indeed, rusting proceeds in an accelerated rate owing to the presence of the tin, for the two metals form a couple. carbonic acid in water
To deprive commercial lead of the silver which it almost always contains, zinc is stirred up with the molten metal ; the zinc dissolves the silver and floats to the it is allowed to harden, and the cake ; The silver and zinc are separated by then removed. distillation of the more volatile zinc ; the lead is freed from zinc by melting it in an oxidising atmosphere, when the more easily oxidisable zinc is first oxidised, and can be
surface of the lead is
removed
as dross.
This
is
Parke's process for desilverising
lead.
The alloy of zinc with copper is termed brass, Muntz metal, and tombac. English brass
beck,
pinchusually
It is and 30 of zinc. made by melting the copper and adding the molten zinc. The addition of nickel (Cu 52 per cent., Zn 23 per cent., Ni 1 5 per cent. ) yields "German silver," of which spoons, forks, and coins are made. Electroplate has usually a basis of this alloy, and is covered with silver by depositing it Zinc coated over from its double cyanide with potassium.
contains
70 per
cent, of copper
MODERN CHEMISTRY
196
with a superficial layer of zinc dilute sulphuric acid, pole of most batteries
amalgam
is
not attacked by
and
is
therefore used as the negative
it
is
only on connecting with some is evolved from the
;
electropositive metal that hydrogen latter, while the zinc dissolves. less
"
Aluminium bronze
"
copper, containing from 2
is
an alloy of
aluminium with
per cent, of the former It resembles gold in colour, and is metal. employed in the manufacture of imitation jewellery. to
1 1
"
and " ferromanganese " are produced by simultaneous reduction of ores of iron and chromium, or Their addition in small quantity to of iron and manganese. "
Ferrochrome
iron improves of manganese
its is
Iron containing about 10 per cent, quality. " as Spiegel iron," for it crystallises
known
in large brilliant plates. Tungsten, too, is to iron to increase its hardness.
sometimes added
" Pewter"
is an alloy of 80 per cent, of lead with 20 per plumbers' solder consists of two parts of lead " " Britannia metal is made of equal parts ; of brass, tin, antimony, and bismuth. " Bronze " is one of the most ancient alloys, and used to It be made by reducing together copper ores and tin ores. often contains twenty-two parts of tin and seventy-eight
cent, of tin; to one of tin
Its hardness is greatly increased by the parts of copper. " Speculum metal," presence of a trace of phosphorus.
astronomical mirrors, is made by alloying thirty-two of copper and one of arsenic. parts of tin with sixty-seven It takes a very high polish. Copper is easily tinned by
for
melting the tin in the vessel, and pouring out the excess this is frequently
"
done
;
to vessels required for cooking.
is an alloy of lead and antimony, conIt expands slightly on 8 per cent of the latter. the mould it takes solidifying, and consequently when cast in
Type-metal"
taining
1
an accurate impression and forms a clean-cut type. The "Pattinson's process" is a rival of the Parke's The lead is melted and process in desilverising crude lead.
allowed to solidify partially
;
the solid portion consists of
ALLOYS
197
The liquid portion contains the silver. the lead may be nearly comrepetition of the process, and an alloy rich in silver may pletely deprived of silver ; nearly pure lead.
By
be obtained, from which the lead
may
be removed by
cupellation.
Osmiridium is a native alloy of osmium and iridium ; it extremely hard, and it is used for pointing gold pens and for the bearings of small wheels. An alloy of platinum with i o per cent, of iridium is the metal employed for is
crucibles.
An alloy of copper and silver is used for coinage ; The alloy English coins contain 7.5 per cent, of copper. must be rapidly cooled, else it ceases to be homogeneous. Gold
also alloyed with
copper for coinage ; pure gold is English standard is eleven parts of gold to one of copper ; in France and the United States, nine of The richness of such an alloy is gold to one of copper. " measured in " carats." Pure gold is " 24-carat gold ; is
a soft metal.
The
" i8-carat gold" contains eighteen
parts of gold
and six of
copper.
The study of the chemistry of metallic alloys was for Jong neglected, but of recent years much has been done. It is curious to think that the successful solution of many chemical problems is to be expected from careful examination of this class of substances, which was the first to engage the attention of the chemists of the remote past.
INDEX ACETIC
acid, 112
Acetylene, 32, 36
INDEX
200
ELECTRIC
Carbamine, 174 Carbides, 36, 190 Carbon, acids of, 112
potential, 23 Electrolysis, 7
Elements, 6
chloride, 58 gas-, 12
28, 29 ,, separation Ethers, 90 Ethylene, 36
hydrides, 32
monoxide, 93 oxysulphide, Carbonates, 106
in
acid, 109 basic, 108 native, 108
,,
,, ,,
34
Chlorates, 142 Chloride of lime, 141 Chlorine, n, 15, 21 hydride, 34, 41 monoxide, 141 ,, ,, peroxide, 143
Chlorochromates, 150 Chlorosulphonic acid, 150 Chromamines, 178 Chromates, 151 Chromic acid, 152 Chromicyanides, 187 Chromium halides, 63 hydroxides, 77, 78
,,
7
Ferrochrome, 196 Ferrocyanides, 185 Ferromanganese, 196
Cerium, 16 of,
of,
FERRICYANIDES, 185
Carborundum, 191 Chemical action, rate
properties of, 26, 27,
,,
Fluorine,
n
hydride, 33, 40
,,
Flux, 16
Formic
acid, 112
GALLIUM, 9 hydroxide, 77 Galvanised iron, 195 Gases, solution of, 3 German silver, 195 ,
,
Germanium, ,,
Gold,
16, 18
hydroxide, 77
10, 12, 23
Graham's Law,
Chromyl
chloride, 150 Classification, 30 Coal-gas, 12
Guanidine, 172
Cobalt, 16, 18 ,, amines, 178 ,, halides, 63 ,, hydroxide, 78 Coinage, 197 Complex groups, oxides of, 86 Complexity, molecular, 45, 99
HALIDES, 50
3
Cupricyanides, 188 Cuprous chloride, 54 Cyanides, 182, 183
,, double, 54 Halogens, hydrides of, 33 Helium, 4 Hydrazine, 42, 86 Hydrazoates, 170 Hydrazoic acid, 41 Hydrides, 30 Hydrocarbons, 45 Hydrocyanic acid, 182 Hydrogen, 12, 24 bromide, 34, 35, 37 chloride, 34, 35, 37 dioxide, 92 fluoride, 33, 35
DISPLACEMENT,
Hydrolysis, 51, 53
Compounds, Copper,
i,
30
9, 16, 18,
23 hydroxide,*77, 78 Cupramines, 179 ,,
Cupric iodide, 56
iodide, 35, 37 liquid, 6
15
INDEX Hydrosulphides, 69, 81, 82, 83 Hydrosulphites, 166 Hydroxides, 69, 71, 72, 73, 74 ,, properties of, 78 Hydroxylamine, 87 Hypobromites, 144 Hypochlorites, 140 Hypoiodites, 134 Hyponitrites, 138 Hypophosphates, 137 Hypophosphites, 136
INACTIVE
gases, 4 Indicators, 75 Indium, 16, 17 ,, hydroxide, 77 "Insoluble" substances, 70 lodates, 134 Iodine, n, 15, 23 halides of, 60 ,, ,, hydride, 34 lodometry, 165
lodonium compounds, 91 Ions, colour of, 64 Iridium, 12 Iron, 16, 18, 19 ,, halides, 63
hydride, 31 hydroxides, 78
,,
,,
KRYPTON,
n
hydride, 31 hydroxide, 74
MAGNESIUM,
8,
16
hydroxide, 77 Manganates, 152 ,,
Manganese, ,,
Mercuric iodide, 56 Mercury, 12, 22 Meteoric iron, 31
Methane,
32,
Mixtures,
i
36
Molybdates, 154
Molybdenum
NASCENT Neon,
halides, 63
state, 39,
42
5
Neutral oxides, 98 Neutralisation, 75 Nickel, 10, 16, 18 ,,
halides, 63
,,
hydride, 31 hydroxide, 78, 79
,,
Niobium, 16 Nitrates, 127 Nitric acid, action ,,
on metals, 95 oxidation with, 97
,,
oxide, 97 ,, peroxide, 98 Nitrides, 37, 169 ,,
134 Nitrogen, 22 Nitrites, ,,
iodide, 59
,,
oxygen compounds chloride, 58
,,
,, hydroxide, 77 Lithium, 8,
,,
Mass-action, 14, 62 Mercuramines, 180
132
16 hydroxide, 77 Lead, 16, 18, 25 chlorides, 62 ,,
,,
39
test,
5
LANTHANUM,
,,
201
Marsh's
18
Nitrous oxide, 95
OSMIRIDIUM, 197
Osmium,
12
Osmocyanides, 187 Osmosis, 116 Oxalic acid, 113 Oxidation, 64 Oxides, 69 formation ,,
of, 80,
Oxygen, 13, 15 Ozone, 23
dioxide, 102 halides, 63
hydroxides, 78
Manganicyanides, 187
PALLADIUM, ,,
12
halides, 64
81
of,
INDEX
202 Palladium hydride, 31 Parke's process, 195 Pattison's process, 196 Perborates, 168 Percarbonates, 168 Perchlorates, 142 Perchromic acid, 167 Periodates, 134 Permanganates, 152 Peroxides, 192 Persulphates, 168 Pewter, 196 Phosphamides, 176 Phosphates, 126 Phosphides, 37, 181 Phosphines, 89
Phosphonium
halides, 65, 66
Phosphorus, 18 ,,
,,
Sodium,
8, 17,
18
,,
dioxide, 92 hydride, 31
,,
hydroxide, 74
,,
Solder, 196 Solubility-product, 83, 84, 85 Solution of gases, 3 Spinels, 100 Steel, 21 Strontium, 8, 16 oxide, 76 ,, Sulphamides, 177 Sulphates, 159
36, 37 hydride, '
Sulphonates, 148 Sulphur, 12, 22 ,, ethers, 90 ,, halides, 60
hydride, 31 Polymerisation, 48 Potassium, 8, 17 ,, hydroxide, 74 tetroxide, 92 ,, Potential, electric, 23
REDUCTION, Rhodium, 12 ,,
,,
Sulphides, 69, 81 Sulphites, 147, 148
halides, 64
Rubidium,
hydroxide, 77, 78 oxide, 79
,,
acids, 133 halides, 64
Platinum, 12 ,,
Silicon, 16, 17 ,, fluoride, 59 Silver, 10, 12, 16, 23
25,
64
8, 17 hydroxide, 74
Ruthenium, 12 Ruthenocyanides, 187
SCANDIUM,
hydride, 33, trioxide, 155 Sulphuric acid, 155 ,,
39
,,
Sulphurous acid, 146, 149 Sulphuryl chloride, 149
TANTALUM,
16
Tellurates, 159 Telluric acid, 159 Tellurides, 69
Tellurium, 12, 22 ,,
halides, 60
,, hydride, 39 Tellurous acid, 149 Thallium, 16, 18 ,, hydroxide, 77 Thermal data, 145 Thio-acids, 130
16, 25 hydroxide, 77 Selenates, 159 Selenic acids, 159 Selenides, 69 Selenious acid, 146, 149 Selenium, 12, 22 halides, 60 ,,
Thionates, 166 Thiosulphates, 164 Thorium, 16
hydride, 39 115 Silicides, 191
,, hydroxide, 77 Tin, 16, 18, 24, ,, chlorides, 62
,,
,,
Silicates,
Thiocarbo nates, 106,
no
INDEX Tin, hydroxides, 77 Tinned iron, 195 Titanium, 16, 17 hydroxide, 77 Tungstates, 154 Tungsten halides, 63 Type-metal, 196
URANATES, 154 Uranium halides, 63
203
WATER,
32, 35, 36
of crystallisation, 53
,,
XENON,
5
YTTERBIUM, 16 Yttrium, 17 ,, hydroxide, 77
Urea, 174 Zixc,
VALENCY,
61
17, 19
hydroxide, 77 Zincates, 78 Zirconium hydroxide, 77 ,,
Vanadates, 129
Vanadium, 16
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