The Effect of Intensive Drying on the Vapor Pressure and Vapor Density of Ammonium Chloride

VoL. 14, 1928

CHEMISTRY: RODEB USH AND MICHALEK

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THE EFFECT OF INTENSIVE DRYING ON THE VAPOR PRESSURE AND VAPOR DENSITY OF AMMONIUM CHLORIDE By WORTH H. RODIBUSH AND JOHN C. MICHALEK CHIMICAL LABORATORY, UNIVzRSITY OF ILLINOIS

Communicated January 14, 1928

One of the authors' recently reported the results of a series of experiments, in which intensive drying appeared to be without effect upon the vapor pressure of ammonium chloride, and a vapor density corresponding to complete dissociation was obtained for material which had been subjected to a long period of intensive drying. Recently there has come to our attention a paper by Smits2 in which results quite different from ours are reported. He finds that the vapor pressure is reduced by intensive drying and that the vapor density of the dry substance corresponds to the formula NH4Cl, or even a higher molecular weight. Numerous writers3 in the past have found difficulty on thermodynamic grounds in accounting for the results of Baker,4 Johnson5 and Smith and Calvert,6 which taken together indicate that intensive drying affects the vapor density but not the vapor pressure. Smits' paper is only a preliminary report and experimental details are lacking but apparently his apparatus and experimental procedure were similar to that used by the authors. In the absence of complete details we should like to comment upon two or three points only. In the first place, it is evident that experiments upon the effect of intensive drying upon chemical substances can only be confirmed if positive results are obtained. The failure to obtain the bizarre results which have been reported in the literature can always be attributed to the neglect of some apparently trivial detail in the technique of drying. The foregoing statement does not hold, of course, in case it is possible to show that the results were due to some chemical reaction as has been done by Bodenstein and Jost7 in the case of the results of Lewis and Rideal8 on the effect of drying on the reaction of hydrogen with the halogens. A similar finding is reported by Balareff9 who has repeated the work of Baker'0 on intensively dried liquids. The authors would be less hesitant in accepting the results reported in the literature on ammonium chloride had they not observed an unmistakable effect produced by intensive drying, viz., an extraordinary retardation in the rate of evaporation and condensation. The temperature must be held constant for several hours before equilibrium is established between the vapor and solid phases. It would seem that this effect would have prevented Baker from obtaining correct results by the Victor Meyer or Dumas methods for vapor density. The experiments of Johnson were not conclusive and are not considered by Smits to

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ZOOLOGY: C. D. BEERS

PROC. N. A. S.

have been carefully performed. Previous to the appearance of this paper by Smits, there has been no report of experimental work which can be taken as conclusive proof that dry ammonium chloride has an abnormal vapor density. Granting that Smits' results are correct they are scarcely less surprising from the thermodynamic point of view than the previous results of Johnson. Smits' results indicate a heat of vaporization per mol of vapor of more than 40,000 cals. at 286°C. At this same temperature he finds a vapor density corresponding to the formula NH4Cl. Since the heat of dissociation of solid ammonium chloride as measured calorimetrically is 40,000 cal. per mol, this would mean that the dissociation of dry ammonium chloride in the vapor state is an exothermic reaction. 1 Paper presented by J. C. Michalek at the Detroit Meeting of the American Chemical Society, September, 1927. 2 A. Smits, Rec. Tran. chim., 46, 445 (1927). 3 Van Laar, Zeit. physik Chem., 62, 194 (1908). Abegg, Ibid., 62, 607 (1908). Wegscheider, Ibid., 65, 97 (1909). 4 Baker, J. Chem. Soc., 65, 615 (1894). Johnson, Zeit. physik. Chem., 65, 38 (1909). 6 Smith and Calvert, J. Amer. Chem. Soc., 36, 1363 (1914). 7 Bodenstein and Jost, Ibid., 49, 1416 (1927). 8 Lewis and Rideal, Ibid., 48, 2553 (1926). 9 Balareff, J. prakt. Chem., 116, 57 (1927). 10 Baker, J. Chem. Soc., 121, 2555 (1922).

SOME EFFECTS OF DIETARY INSUFFICIENCY IN THE CILIATE DIDINIUM NASUTUM By C. DALZ BsZRS' ZO6LOGICA LABORATORY, JOHNS HopiuNs UNIvERsITY Communicated January 3, 1928

To an elucidation of the normal life-cycle of an infusorian, a critical examination of the relation of the organism to its environment and a thorough understanding of the cultural requirements of the organism are prerequisite. Evidence is accumulating which indicates that in many genetic studies on infusoria precise knowledge of the cultural demands of the experimental animals was wanting and that the outcome of the experiments, usually the degeneration and death of the animals, was erroneously interpreted. Maupas,2 for example, observed progressive degenerative changes in a number of infusoria after long-continued culture and considered such changes to be the result of intrinsic aging and not of unfavorable environment, a conclusion which is valid only upon satisfac-