A REVISION OF THE ATOMIC WEIGHTS OF IODINE AND SILVER. IIQ 



meter. A quartz condensing tube was used in these distillations, and the final 

 product was collected in a quartz vessel. In this way the introduction of silica 

 and alkalies from glass vessels was avoided. Fused quartz vessels have already 

 been shown to be essentially insoluble in acid solutions.^ 



The reaction between iodine and fuming nitric acid proceeds slowly at ordi- 

 nary temperatures, with the formation of oxides of nitrogen and nitro-iodic acid. 

 Heat hastens the reaction and also breaks up the nitro-iodic acid into nitric oxide, 

 iodine, and iodic acid. If the nitric acid is in large excess the iodine is converted 

 into iodic acid without loss, and the iodic acid remains insoluble in the residual 

 concentrated nitric acid. If the iodine is in excess, the reaction proceeds until 

 the nitric acid is so dilute, owing to the production of water in the reaction, as to 

 be without further effect upon the iodine, although the acid is still so concen- 

 trated that the iodic acid remains essentially insoluble. Nitric acid of this 

 concentration dissolves considerable quantities of iodine, however. 



Since the largest quartz vessel at first available was a looc.c. transparent fused 

 quartz flask, the most convenient method for making the iodic acid was found to 

 be to treat a large quantity of iodine in the flask with successive portions of 

 fuming nitric acid. After the introduction of the iodine, nitric acid was dis- 

 tilled directly into the flask through the quartz condenser. The flask was then 

 warmed until the nitric acid was spent. The spent acid was removed as com- 

 pletely as possible by drainage, and was replaced by fresh acid, and the process 

 was repeated until the iodine appeared to be completely oxidized. Dissolved 

 iodine was recovered from the spent acid by dilution. After the removal of the 

 last portion of the acid, the iodic acid was dissolved in the smallest possible 

 amount of the purest water and the solution was evaporated to dryness in a 

 dish of fused quartz in order to expel nitric acid and unchanged iodine, for the 

 removal of nitric acid by crystallization is very slow. During this evaporation 

 the dish was placed upon a large watch glass on a sand bath, and was surrounded 

 by a large bottomless beaker. The dish was further protected by being cov- 

 ered with a bottomless flask, through the neck of which a current of pure dry 

 air was introduced in order to hasten evaporation. The air was freed from 

 organic matter by passing over hot copper oxide in a hard-glass tube, and was 

 purified and dried by means of a solution of potassium hydroxide and solid 

 caustic potash. The purifying apparatus was constructed wholly of glass. 



The residue from the evaporation was dissolved in the purest water and evap- 

 orated in the quartz dish with the same precautions as above until a film of 

 soUd appeared on the surface of the liquid. This solid is not iodic acid, but is 

 probably a compound having less water, since it was necessary to induce the 

 crystallization of the acid itself by inoculation. If left to itself the acid crystal- 

 lizes very slowly, some days being necessary for the establishment of equilib- 



* Mylius and Meusser; Zeit. anorg. Chem., 44, 221 (1905). Baxter andHines: Jour. Amer. 

 Ckem. Soc, 28, 1565 (1906); Zeit. anorg. Chem., 51, 205. (See page 36.) 



