Roberts — Action of Reducing Agents on Iodic Acid. 157 



III. Action of Iodine on Iodic acid in presence of Hydro chloric 



acid. 



Some light is thrown upon the reaction just established by 

 the behavior of free iodine in a mixture of iodic and hydro- 

 chloric acids. 



Although a solution of iodine in iodic acid turns starch blue, 

 and also one of iodine in hydrochloric acid, if the solutions be 

 mixed, the starch immediately loses its color, but regains it on 

 the addition of alkaline carbonate. Also, if a colorless mix- 

 ture of iodic and hydrochloric acids be taken, and aqueous 

 iodine added gradually from a burette, the first effect of the 

 addition is to make a colorless liquid in which the presence of 

 iodine can be proved only upon addition of an alkaline carbo- 

 nate. Further addition of the iodine gives a yellow liquid 

 whose properties and reactions seem identical with that ob- 

 tained by putting together iodic and hydrochloric acids and 

 potassium iodide. This same liquid may be produced by allow- 

 ing iodine to dissolve slowly in the cold in a mixture of dilute 

 hydrochloric and iodic acids. 



Apparently, then, the action of reducing agents is to set 

 free iodine from the iodic acid, and this dissolves in a mixture 

 of iodic and hydrochloric acids to form iodine chloride. Two 

 experiments were made to determine the proportions in which 

 the iodine and iodic acid unite in this reaction. Solid iodine, 

 in carefully weighed quantity, was allowed to dissolve in a 

 mixture of the acids, then the acid was neutralized with alka- 

 line carbonate, and the iodine set free estimated by means of 

 arsenious acid. The molecular proportions of iodic acid to 

 iodine as found were as follows : 



HI0 3 : I 



] : 4-02 

 1 : 4-07 



The same proportions were obtained by direct titration of 

 iodic acid against a solution of iodine in hydrochloric acid of 

 known strength. The operation was performed in a flask, a 

 definite quantity of iodic acid being first introduced and then 

 the solution of iodine added from a burette until, upon shak- 

 ing the flask, the presence of free iodine was indicated by the 

 characteristic color given to chloroform. 



The molecular proportions found were : 



HI0 3 : I 



1 : 4-02 

 1 : 4-06 



