CHEMISTRY. 



345 



were collected and evaporated in a quartz dish and a small residue 

 of cadmium salt was converted to sulphate and weighed. Complete 

 deposition of the cadmium was never secured. 



The advantages of this cell were its small size, the fact that any plati- 

 num dissolved by the chloride liberated at the anode was quickly 

 deposited upon the cathode, so that no loss occurred, and the fact that 

 no transference of material was involved, since the boat containing the 

 fused salt was introduced bodily into the cell, to be removed when 

 electrolysis was complete. 



The cadmium material was purified in various ways : by electrolysis 

 with a dissolving anode, by fractional precipitation with hydrogen 

 sulphide, by crystallization of cadmium bromide, and always finally 

 by crystallization of the chloride. The purity of the various samples 

 was followed by photography of the spark spectrum in the visible 

 and ultra-violet regions. 



The result is in exact agreement with the earlier one of Baxter, Hines, 

 and Frevert, obtained by determining the halogen in the anhydrous 

 chloride and bromide, 112.417. It is difficult to account for the 

 discrepancy between our electrolytic results and those of Hulett. 



Mr. Hartmann and Mr. M. R. Grose have extended the research to 

 the determination of the cadmium in cadmium bromide, and their 

 preliminary results confirm the value obtained from the chloride. 



The method in general has proved satisfactory far beyond expecta- 

 tion as regards both accuracy and speed, and seems capable of applica- 

 tion to many other metallic halides. It is planned to do this as soon 

 as possible. A portion of the apparatus used in this research was 

 provided by a grant from the Elizabeth Thompson Science Fund. 



The Atomic Weight of Arsenic. 



Mr. G. L. Wendt continued the investigation upon the reduction of 

 arsenic trioxide by iodine pentoxide (see Year Book No. 11), but owing 

 to new difficulties no further evidence is ready for presentation. 



The Vapor Pressure of Iodine. 



Mr. M. R. Grose investigated the vapor pressure of iodine by the 

 "air-current" method, at temperatures from 50° to 95°, with the results 

 shown herewith. 



A curve plotted with these results joins very satis- 

 factorily with curves drawn from the results of Bax- 

 ter, Hickey, and Holmes, up to 50°, and those of 

 Ramsay and Young, which are dependable to tem- 

 peratures somewhat below 100°. 



Mr. C. F. Hawkins was able to prove experimen- 

 tally that arsenic trioxide adsorbs no weighable 

 amount of air on its surface. This is the third sub- 

 stance that has been especially investigated from 

 this point of view in the Harvard Laboratory, and 

 in no case has adsorption of air been detected. 



