132 • RESEARCHES UPON ATOMIC WEIGHTS. 



PURIFICATION OF IODIC ACID AND SILVER FOR THE SECOND 



SERIES OF ANALYSES. 



Two new specimens of iodic acid were prepared. In order to determine 

 whether crystallization of the iodic acid alone was sufficient purification, Sample 

 II was made from iodine which had been purified by only a single distillation 

 from solution in an iodide, and then by one from water, while the nitric acid 

 was once distilled through a quartz condenser with no special attempt to remove 

 chlorine. A portion of the iodic acid was prepared in the transparent fused 

 quartz flask as already described. The remainder was made in a large opaque 

 quartz dish nearly one liter in capacity. The inside of this dish had been abraded 

 with sand to break the edges of the bubbles, and had been digested for hours with 

 acid solutions to remove soluble impurities. The combined specimens of acid 

 were crystallized at least ten times in dishes of transparent fused quartz, with 

 centrifugal drainage, until free from the organic odor previously mentioned. 

 In the preparation of this sample the solutions were always heated and evap- 

 orated upon an electric stove under a large Victor Meyer funnel, instead of in 

 the special evaporating apparatus previously described. 



The second specimen of acid was prepared from iodine resulting from the 

 decomposition of the iodine pentoxide in the water determinations. It was first 

 dissolved in pure sulphurous acid and then set free from solution by distilla- 

 tion with recrystallized potassium permanganate, a little less permanganate than 

 was necessary to set free all the iodine being employed. The product was thus 

 distilled once from a dilute solution of an iodide. Finally the iodine was once 

 distilled from pure water. The nitric acid for this preparation was carefully 

 freed from chlorine by double distillation with a quartz condenser as previously 

 described. The iodine was converted into iodic acid by treatment with the 

 nitric acid in the large opaque quartz dish used for the preparation of Sample 

 II. Before the crystallization of the iodic acid was commenced, the powder re- 

 sulting from the treatment of the iodine with nitric acid was drained and heated 

 on the electric stove until apparently all nitric acid had been expelled. Then it 

 was heated to 300° in a current of pure dry air in small portions in a platinum 

 boat. The resulting iodine pentoxide was dissolved in water and at least ten 

 times recrystallized in quartz dishes from solution in the purest water, with cen- 

 trifugal drainage in platinmn Gooch crucibles. In spite of the drastic treatment 

 to which the iodine had been subjected before conversion into iodic acid, the 

 mother-liquors of the first crystallization were by no means free from the 

 organic odor previously observed, although nitric acid seemed to have been 

 completely removed. This odor disappeared gradually during crystallization as 

 before, and the final product was free from odor. This specimen is designated 

 Sample III, 



