CHEMISTRY. 335 



It has also shown the necessity of greatly improving the experimental 

 methods of determining the magnitude of the intensities of the reflec- 

 tions. Especial attention is now being given to the perfection of these 

 methods. 



Richards, Theodore W., Harvard University, Cambridge, Massachusetts. 

 Continuation of exact investigation of atomic weights and other -physico- 

 chemical properties of elements and of simple compounds. (For previous 

 reports see Year Books Nos. 2-18.) 



During the past winter the activity in the Wolcott Gibbs Memorial 

 Laboratory was nearly normal for the first time in four years. Eleven 

 investigations were conducted ; many of these brought definite results, 

 while others will be continued in the coming year. 



(1) Atomic Weight of Gallium. 



]\Ir. W. M. Craig, having made for the last two years a thorough 

 study of the purification of gallium, proceeded to prepare with gTeat 

 pains and much expenditure of time a larger quantity of this rare ele- 

 ment from material from the Bartlesville Zinc Company, Oklahoma. 

 At the close of the academic year he had a number of specimens of the 

 purest gallium chloride hemietically sealed in glass bulbs ready for 

 analysis. There is every reason to believe that the ascertaming of the 

 exact percentage composition of these specimens will give a far better 

 basis for the atomic weight of gallium than any thus far provided. 



(2) Atomic Weight of Aluminum. 



Dr. Henry Krepelka (on a Government scholarship from Czecho- 

 slovakia) studied the atomic weight of aluminum by the analysis of 

 pure aluminum bromide. The purest obtainable metal was treated 

 with thoroughly purified bromine vapor and the resultmg aluminum 

 bromide was fractionally distilled in vacuo with the utmost pains to 

 exclude water or other impurities. IMany precautions were taken, the 

 description of which is beyond the scope of this brief report. The final 

 result for the atomic weight of aluminum was 26.963, a value over 0.5 

 per cent below that previously accepted. 



(3) Separatiox of Lead Isotopes. 



The separation of isotopes is at present one of the most insistent prob- 

 lems concerning atomic weights and the periodic system. With the 

 help of Mr. Harold S. King, a careful study of possible methods was 

 undertaken. Lord Rayleigh's mathematical work on diffusion being 

 applied to the case of lead shows that separation by diffusion would be 

 a very slow and almost impossible procedure, at least by ordinary 

 methods. Centrifugal treatment was rejected for the same reason. 

 Among chemical processes the only one for which success has been 

 claimed is the Grignard reaction. A definitive test as to this possi- 

 bility seemed to be the most immediate need and accordingly the frac- 



