ACADEMY OP SCIENCES] BIOGRAPHY 3 



other foreign substances greatly influenced the proportions. These foreign bodies were proved to act cata- 

 lytically, and retard or hasten the change from amorphous to soluble sulfur. The establishment of this con- 

 clusion at once afforded a basis for explaining a large proportion of the apparent inconsistencies in the older 

 as well as the more recent observations. In connection with this work, the proportions of amorphous sulfur 

 present in equilibrium at various temperatures were measured. 



In the fifth paper, studies of some other peculiarities in the behavior of melted sulfur were described, and 

 all the results were shown to harmonize with a theory of the relation of the two liquid forms as dynamic 

 isomers. 



Precipitated sulfur was the subject of the sixth paper, and it was shown that, when first liberated, the sulfur 

 consists of droplets of liquid amorphous sulfur. In presence of weak acids, or in neutral or alkaline solutions, 

 this changes wholly to crystalline, soluble sulfur. In presence of active acids, the amount of amorphous sulfur 

 surviving in the final product is proportional to the concentration of the acid. 



In the seventh paper, the generally accepted melting points (or freezing points) of the various forms of 

 sulfur, determined before the complex nature of the problem which such measurements involved was in the 

 least suspected, were subjected to revision, and the correct values, in harmony with the theory, were given. 



The work on Vapor Pressures (carried out in collaboration with Prof. A. W. C. Menzies) is described in 

 seven papers. The first two deal with a simple device, named the "submerged bulblet," by which boiling 

 points and vapor pressures of liquids and of non-fusing solids may be determined with the use of only minute 

 amounts of material. 



In the third and fifth papers, forms of apparatus for the exact study of vapor pressures, and named 

 respectively the static and dynamic "isoteniscope," are described. To ascertain the possibilities of the methods, 

 values for water, which agree with the best previous determination, were obtained by the static method, and 

 values for benzene and for ammonium chloride by the dynamic method. 



The fourth paper describes a determination of the vapor pressures of mercury. These were made because 

 exact values were required for the subject of the sixth paper, and the existing results (e. g., those of Regnault, 

 Ramsay and Young, and others) were highly inconsistent with one another, and the methods used were open 

 to serious criticism. 



The sixth paper deals with the constitution of calomel vapor, a matter long but inconclusively discussed 

 by chemists. By making measurements of the vapor pressures of mercury, of calomel, and of a mixture of the 

 two, and applying the laws of chemical equilibrium to the resulting data, it was shown conclusively that the 

 vapor is wholly composed of mercury and corrosive sublimate. The close quantitative correspondence showed 

 that in these measurements the order of accuracy was much higher than in any previous measurements of vapor 

 pressures at elevated temperatures. 



The seventh paper shows that, as the laws of chemical equilibrium applied to the result of the preceding 

 paper predict, calomel, when dried in the most rigorous manner, exercises, even at high temperature, no meas- 

 urable pressure whatever. This is the only successful experimental confirmation of a familiar and important 

 application of the theory. 



In 1911 he was called to Columbia University, New York City, as professor of chemistry 

 and administrative head of the department of chemistry, succeeding Prof. C. F. Chandler, 

 who had retired in 1910. He continued in this position till his failing health compelled him 

 to retire in the fall of 1919. He died at Edinburgh, on September 8, 1922. 



At Columbia University he directed his attention chiefly to a study of the vapor pressures 

 and densities of the ammonium halides. Some years before, Baker had shown that thoroughly 

 dry ammonium chloride vaporizes without dissociation (J. Chem. Soc, 65, 615 (1894) and 73, 

 422 (1898). It had long been known that ordinary ammonium chloride, containing a trace 

 of moisture, is almost completely dissociated when it is heated somewhat above its point of 

 vaporization. Professor Smith and his collaborators devised methods for determining the 

 density of saturated vapors of ammonium halides and demonstrated that the dissociation is 

 very far from complete in such conditions. The dissociation of ammonium chloride does not 

 exceed 67 per cent at 280° to 330°, while the dissociation of ammonium bromide and ammonium 

 iodide is still less. They also demonstrated that the transition point of ammonium cldoride is 

 the same for the carefully dried as for the undried salt. The purpose of these later experi- 

 ments was to find some explanation for the anomalous fact that the vapor pressure of carefully 

 dried ammonium chloride, which vaporizes without dissociation, is the same as that of the 

 partially dissociated chloride. A satisfactory explanation was not found, but the suggestion 

 of Wegscheider (Z. anorg. Chem. 103, 207 (1918)), that the constancy of the vapor pressure 

 was due to the fact that the dried salt does not undergo a transition at 184.5°, was shown to 

 be untenable. 



