350 CARNEGIE INSTITUTION OF WASHINGTON. 



CHEMISTRY. 



Baxter, Gregory P., Harvard University, Cambridge, Mass. Determination 

 of atomic weights. (For previous reports see Year Books Nos. 3-13.) 



During the past year papers were published embodying results upon 

 the atomic weights of cadmium, praseodymium, and lead, and upon 

 the vapor-pressure of solid iodine. 



Dr. F. L. Grover continued his investigation upon the atomic weights 

 of non-radioactive lead, by the exanunation of additional samples of 

 material (see Year Book No. 13). In all, 11 specimens of lead salts 

 from man}' different geographical and mineralogical sources were 

 prepared and found to be identical, so far as could be determined by 

 spectroscopic examination and by analysis of the chloride and bromide. 

 The atomic weight of common lead found in this way is 207.20 (Ag = 

 107.880). No indication was found that ordinary lead is composed 

 either wholly or in part of isotopes of different atomic weights. 



As a check upon the analysis of lead chloride and bromide by com- 

 parison with silver. Dr. Grover attempted to synthesize lead chromate 

 quantitatively from metaUic lead. While this salt possesses an unusu- 

 ally small solubility in neutral solutions, it was found to occlude and 

 hold soluble lead salts very tenaciously, even when precipitation is 

 carried out in very dilute solution. 



Attention was next turned to the electrolytic determination of lead 

 in the chloride by deposition in a mercury cathode. A long search was 

 necessary to find a suitable washing liquid for lead amalgam. Finally, 

 after Mr. Grover had been obhged to discontinue the research, Mr. 

 Leon W. Parsons found that when especially pure ether is employed, 

 the attacking of the amalgam, which ordinarily occurs, was hardly 

 perceptible. No analytical results have as yet been obtained. 



Interest in the identity of material from different sources, aroused 

 by recent radioactive developments, made it desirable to compare 

 nickel from terrestrial and meteoric sources, as has recently been done 

 in the case of iron by Baxter and Thorvaldson and by Baxter and 

 Hoover (see Year Books Nos. 9 and 11). This investigation was 

 undertaken by Mr. Parsons. 



Since in earUer work in the Harvard Laboratory by Richards and 

 Cushman, nickelous bromide was the compound analyzed, in this work 

 reduction of nickelous oxide in hydrogen was chosen, in order to pro- 

 vide a comparative method and furnish a direct ratio to oxygen. 



The source of the terrestrial material was commercial nickelous 

 nitrate, that of the meteoric material was the ''Cumpas" meteorite, a 

 generous portion of which was given us by Professor John E. Wolff, 

 of the Harvard University Museum. Both samples were carefully 

 freed from cobalt by crystalhzation of nickel ammonia nitrate, and 

 finally, after nickel nitrate had been prepared from electrolytic metal, 



