•472 (jhoch and Blwvn nthal — Iodic Acid Process. 



and out of all proportion to any possible chloride contamination 

 of the standard bromide. The fact that the chlorine proves to 

 be invariably high and the bromine generally low, suggests the 

 probability that the iodic acid reaction fails to remove all the 

 bromine in the process of boiling. 



Bromine was found in the silver chloride obtained from the 

 combined residues of several determinations by applying the 

 chloroform test to the water extract of the sodium carbonate 

 fusion of these residues, after acidulating with sulphuric acid 

 and adding a drop or two of chlorine water. Furthermore, in 

 a special experiment in which pure potassium bromide was 

 treated according to the procedure outlined, the titration 

 figures of the excess of iodate corresponded to only 0-1 945 

 grm. of potassium bromide out of 0198-i grm. taken ; while, 

 after treatment with sulphur dioxide followed by nitrogen tri- 

 oxide, and boiling until all iodine had been expelled (as shown 

 by the starch test applied to the cool solution), silver nitrate 

 precipitated from the solution silver bromide equivalent to 

 0-0036 grm. of potassium bromide. The 0'1945 grm. of the 

 potassium bromide indicated by the determination of the iodate 

 and the 0-0036 grm. equivalent to the silver bromide precipi- 

 tated after reduction make up 0'1981 grm. of the - 1984 grm. 

 taken. In this experiment, therefore, the deficiency of bro- 

 mine and the excess of chlorine noted were plainly due to the 

 retention of bromine, after the iodic acid treatment, in some 

 combination such that the process of reducing the residual 

 iodic acid and expelling the iodine left it in condition to be 

 precipitated as silver bromide, which was counted as silver 

 chloride. 



The combination of iodine with bromine in this experiment 

 and of iodine with bromine and chlorine in the experiments of 

 the table, would account for the observed deficiencies in bro- 

 mine and excess in chlorine ; and a little consideration shows 

 that the conditions of the process are favorable to the forma- 

 tion of such combinations. Thus free bromine and free 

 iodine, both products of the main reaction, may readily com- 

 bine to form iodine monobromide, 



HI0 3 + 5HBr = 2Br 2 + IBr + 3H q O. 



Furthermore, Roberts* has shown that iodic acid, iodine, and 

 aqueous hydrochloric acid react to form iodine monochloride, 

 according to the reaction 



HI0 3 + 2l a + 5HC1 = 3H 2 + 5IC1, 



and it may reasonably be expected that in the reaction of iodic 

 acid and hydrobromic acid in presence of free iodine (pro- 

 * This Journal (3), xlviii, 1, 58. 



