376 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 54 



From the acetate, 1102(0211302) 2.2H0O, the following percentages of 



UoOc were obtained 



4.601 

 1.869 

 3.817 

 10.182 

 4.393 

 2.868 



Mean, 66.3569, ± .038 



Hence U = 239.73. 



The acetate also yielded the subjoined percentages of carbon and of 

 water. Assuming tbat the figures for carbon were calculated from known 

 weights of dioxide, with C = 12 and = 16, I have added a third column, 

 in which the carbon percentages are converted into percentages of CO,: 



CO.. 

 41.323 

 41.433 

 41.433 

 40.700 



Mean, 21.265, ± .187 Mean, 11.24 Mean, 41.222, ± .092 



From these data we get the following values for the molecular weight 

 of uranyl acetate : 



From percentage of UA 425.827, ±: .1678 



From percentage of CO, 426.993, ± .9530 



From percentage of H.0 423.603, ± 3.7250 



General mean 425.861, ± .1651 



Hence 17 = 239.77. 



In the posthumous paper of Zimmermann, edited by Kriiss and Alibe- 

 goff,' the atomic weight of uranium is determined by two methods. 

 First, UO2, prepared by several methods, is converted into UaOg by heat- 

 ing in oxygen. To begin with, UgOg was prepared, and reduced to TJO2 

 by ignition in hydrogen. When the reduction takes place at moderate 

 temperatures, the UOo is somewhat pyrophoric, but if the operation is 

 performed over the blast lamp this difficulty is avoided. After weighing 

 the UOj, the oxidation is effected, and the gain in weight observed. The 

 preliminary TJ^Og was derived from the following sources : A, from ura- 

 nium tetroxide; B, from the oxalate; C, from uranyl nitrate; D, by 



' Ann. Chem., 232, 299. 1S86. 



