RICHARDS AND MERIGOLD. ATOMIC WEIGHT OF URANIUM. 375 



Analysis of Uranyl Iodate. 



100.00% 100.00% 



In determining the composition of the iodate, a weighed quantity of 

 the substance was used, and the percentage composition by weight cal- 

 culated in the usual manner. For an atomic weight determination, 

 however, any method which involves the original weight of a salt 

 crystallized from solution as a factor in the calculation must of course be 

 avoided on account of the ever present possibility of included mother 

 liquor. It was necessary, then, to determine directly the ratio of 

 iodine to uranium, or to uranium oxide. To determine the uranium, 

 advantage was taken of the behavior of the iodate on ignition. When 

 heated, the iodate is decomposed, water, oxygen, and iodine being given 

 off, leaving uranium oxide. The process was carried on in an ordinary 

 combustion tube of hard glass, a current of dry air being passed through 

 the tube. Since Zimmermann has shown that the green oxide under- 

 goes partial reduction at high temperature unless in an atmosphere of 

 oxygen, * a stream of oxygen was finally passed through the tube. The 

 oxide was then cooled in an atmosphere of oxygen. Treated in this 

 way, the decomposition of the iodate is not complete. Some iodine 

 always remained in the oxide, even when the heat was maintained for 

 three hours at a temperature just below the softening point of the com- 

 bustion tube. To correct for this amount of iodine, the oxide was 

 weighed, dissolved in dilute nitric acid, and the iodine precipitated as 

 argentic iodide. The amount of iodine found in this way varied from 

 0.1% to 1.0% of the total iodine, according to the duration of the period 

 of ignition. 



Iodine was determined in another sample of material exactly similar 

 to that used for the uranium. The method was, briefly, reduction of 

 the iodate by sulphurous acid, and precipitation with silver nitrate. 

 Stas has shown that silver iodate can be converted completely and with- 

 out loss into silver iodide by the use of sulphurous acid,f and the same 



* Annalen der Chemie u. Pharmacie, 232, 287 (1886). 



t Untersuchungen iiber die Gesetze der chemischen Proportionen liber die 

 Atomgewichte u. ihre gegenseitigen Verhaltnisse, J. S. Stas. Aronstein's transla- 

 tion, p. 69. 



