RICHARDS AND MERIGOLD. — ATOMIC WEIGHT OF URANIUM. 377 



to believe that at the temperature employed any of the iodine can exist 

 as iodic acid, it is impossible to prove the point experimentally. The 

 uncertainty in regard to this point renders the use of the method inadvis- 

 able where the greatest possible accuracy is desired. Hence none of 

 these analyses have any significance as a basis for computing the atomic 

 weight of uranium. 



Besides the bright yellow, slightly soluble iodate, we prepared a paler 

 yellow, more soluble, and more highly hydrated salt, which suffers transi- 

 tion quickly into the earlier compound at a high temperature and more 

 slowly at a low temperature. Double iodates with sodium and potas- 

 sium were also prepared. Some of our observations were inconsistent 

 with the published record concerning the subject ; but in spite of our 

 desire to clear up the uncertainty and to study the rather intei-esting 

 transition phenomena, we abandoned the iodates because none of them 

 gave promise of a precise basis for the determination of the desired 

 atomic weight. 



The next compound investigated was the oxalate, which has the com- 

 position UOoCoOi' SHoO. Owing to the comparatively slight solubility 

 of this compound it can be obtained in a state of great purity by a few 

 crystallizations. 



The best method of analysis is that of dry combustion, the carbon 

 dioxide being absorbed in potash in the usual manner. The uranium 

 is left in the combustion tube as the green oxide, UgOg, and consequently 

 can be compared directly with the weight of carbon dioxide obtained. This 

 obviates the necessity of using the weight of the oxalate as a factor in 

 the calculation of the atomic weight, and so eliminates the error due to 

 included water. As already mentioned, this method has been used by 

 Klbelmen and Peligot in their determination of the atomic weight of ura- 

 niura. There is in this method a possible source of error, difficult of 

 detection and correction, but none the less dangerous, in the possibility 

 that the uranium oxide may after combustion still retain traces of carbon. 

 Moreover, it became evident, after a few analyses had been made, that 

 combustion analysis, as ordinarily conducted, is an exceedingly question- 

 able method where great accuracy is desired. The great difficulty in 

 obtaining absolute " blanks " is well known. Our experience amply 

 confirmed the observations of Mabery,* Auchy,t and others in regard to 



* Inaccuracies in the Determinations of Carbon and Hydrogen of Combustion, 

 C. F. Mabery, Journal Am. Chem. Soc, 20, 510 (1898). 



t George Aiichy, Journal Am. Chem. Society, 20, 243 (1898). 



