1 90 



REPORTS 01^ INVESTIGATIONS AND PROJi;CTS. 



The conditions of precipitation were varied without appreciable effect. No 

 evidence of occlusion of either iodide or silver salts could be detected. The 

 results of these analyses confirm with great exactness the first series of deter- 

 minations, ten analyses giving an average ratio of silver to iodine pentoxide 

 of 0.646217, with an extreme difference of only 0.002 per cent. From this 

 ratio, after correction for the impurity of water, the atomic weight of silver 

 referred to oxygen is calculated to be 107.850. 



This value is lower than is to be expected and the problem is being further 

 investigated. The preliminary results of the research are now in process of 

 publication in the Journal of the American Chemical Society and in the 

 Zeitschrift fiir anorganische Chemie. 



Mr. R. H. Jesse, Jr., has continued the investigation upon the atomic 

 weight of chromium, by analysis of silver dichromate. This salt was pre- 

 pared from pure silver nitrate and either purified potassic dichromate or 

 chromic anhydride, and was crystallized from nitric acid of different concen- 

 trations. It was dried by being heated to 200° C. for some time in a current 

 of dry air. The silver content of the salt was found, after solution in dilute 

 nitric acid and reduction with sulphurous acid, by precipitation as silver 

 bromide or chloride. The salt, after being dried as above, was found to con- 

 tain traces of both nitric acid and water, which were expelled from weighed 

 quantities of the salt by fusion in a current of dry air, and were collected in 

 weighed tubes containing caustic potash and phosphorus pentoxide. The 

 correction thus obtained varied only slightly with the concentration of the 

 acid from which the salt was crystallized. 



The analyses of the different samples of material, after correction for the 

 water and nitric acid, yielded the following results, upon the assumption that 

 the atomic weight of silver is 107.88 : 



The analysis of silver chromate by Dr. Mueller indicated the value 52.01 

 for the atomic weight of chromium, a highly satisfactory agreement. The 

 two investigations upon silver chromate and silver dichromate are being pub- 

 lished in the Proceedings of the American Academy of Arts and Sciences. 



The analysis of silver arsenate, begun last year by F. B. Coffin, has been 

 completed. In this research silver arsenate, prepared by precipitation, was 



