376 PROCEEDINGS OF THE AMERICAN ACADEMY. 



method applies equally well to uranium iodate. The iodate was sus- 

 pended in 200 c.c. of water acidified with 20 c.c. sulphuric acid, cooled in 

 ice to 0°, and pure sulphur dioxide was passed in until the solution 

 smelled strongly of this reagent. The flask was then removed from the 

 ice and shaken occasionally. From three to four hours is required 

 before complete reduction takes place and the last traces of iodate go 

 into solution. When completely reduced, silver nitrate is added, and 

 heated to 60° in order to cause the more coherent deposition of the 

 jjrecipitate.* Thus it was found possible to convert the" insoluble iodate 

 into soluble iodide without loss of iodine. 



In this way the ratio of uranium oxide to iodine may be determined, 

 regardless of the presence of occluded water in the iodate used, provided 

 that the amount of water occluded be exactly the same in each of the 

 samples. It would obviously be more satisfactory to determine both 

 uranium and iodine in the same sample, provided a sufficiently simple 

 method could be found. 



The following method was found to fulfil the required conditions 

 fairly well. A quantity of the iodate was placed in a boat in a com- 

 bustion tube, to one end of which was attached, by a ground glass joint, 

 a weighed U-shaped tube. The free end of this tube was drawn out and 

 fused to a smaller tube which dipped into a solution of sulphurous acid. 

 On heating the iodate in a stream of air and oxygen, the salt was decom- 

 posed and the iodine was carried over and condensed in the U-tube, 

 which was packed in ice. The small quantity of iodine vapor not con- 

 densed was collected in the sulphurous acid and precipitated as silver 

 iodide. The heating: was contiuued for an hour after no more iodine 

 could be seen coming off. The end of the U-tube was then sealed by 

 fusing off the small tube, and the other end was closed by a ground glass 

 stopper immediately after disconnecting from the combustion tube. In 

 this way about ninety-nine per cent of the total iodine was weighed 

 directly as free iodine. Of course the small amount of iodine remaining 

 in the oxide after ignition had to be determined separately, as already 

 described. By this method the amount of iodine found was practically 

 identical with that found by the sulphurous acid method. 



In determining the iodine present in the oxide after ignition, it has 

 been assumed that the iodine is present as iodide. Although it is hard 



* When silver iodide is precipitated in the presence of sulphurous acid, the 

 supernatant liquid does not become clear enough to filter even after several days, 

 unless heated to 60°. 



Vide Stas, " Untersuchungen," p. 69. 



