Roberts — Action of Reducing Agents on Iodic Acid. 153 



tubes varying from a saturated solution containing about 50 

 grams to 25 cubic centimeters to a rather dilute solution con- 

 taining not more than 5 grams to 25 cubic centimeters. There 

 was no apparent absorption as the gas passed up through the 

 liquid, but after the nitric oxide had been standing over the 

 iodic acid for a few moments, iodine appeared on the surface 

 of the liquid. This deposit gradually increased in amount 

 and the liquid rose in the tube, reaching its maximum in 24 

 hours or less,- depending on the amount of gas used. 



The result of my experiments, then, has been to show that 

 nitric oxide is absorbed by solutions of iodic acid of any de- 

 gree of strength, but the reaction takes place slowly even when 

 the gas is confined over the acid, and not at all when passed 

 rapidly through the solution. 



II. The Action of Reducing Agents on Iodic Acid in pi esence of 

 Hydrochloric Acid. 



It has already been stated that when the nitric oxide was col- 

 lected over iodic acid mixed with dilute hydrochloric acid, the 

 gas was absorbed, but there was no liberation of iodine, and 

 in some cases an odor like that of chlorine was observed when 

 the tube was opened. A similar phenomenon was noticed 

 with several other reducing- agents. It is well known that 

 iodic acid with strong hydrochloric acid, or heated with dilute 

 hydrochloric acid, forms iodine chloride and may set free 

 chlorine, but in these experiments the dilute acids were used 

 in the cold, and there was no change apparent until the reduc- 

 ing agent was added. Besides the nitric oxide, other sub- 

 stances which had a similar effect were potassium iodide, 

 sodium thiosulphate, arsenious oxide, ferrous sulphate, stan- 

 nous chloride, and potassium sulphocyanide. If the reducing 

 agent was added in a very concentrated form, iodine was some- 

 times evolved, and in many cases traces of iodine would first 

 form where the reagent touched the liquid, but would disap- 

 pear on shaking, and a light yellow liquid would result with an 

 odor like that of chlorine. 



The first explanation of this phenomenon that suggested 

 itself was that the iodic acid was not immediately completely 

 deoxidized by the reducing agent but was first transformed to 

 a lower oxide of iodine* which was more active and therefore 

 more easily acted upon by hydrochloric acid than the iodic acid 

 itself, and that the chlorine thus set free united wholly or par- 

 tially with the iodine formed by the first reduction. It was 

 with the object of studying the reduction of iodic acid in the 

 presence of hydrochloric acid that some experiments were 



* Gmelin-Kraut, Anorganische Chemie, I, 2, 290-292. 



