Gooch and Blumenthal — Iodic Acid Process. 469 



Art. XLI. — The Iodic Acid Process for the Determination 

 of Bromine in Halogen Salts / by F. A. Gooch and P. L. 

 Blumenthal. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — ccxxxvi.] 



The oxidation potential of a solution of chlorine in potas- 

 sium chloride and water is, according to Bancroft,* about 0"241 

 volt higher than that of a solution of bromine in potassium 

 bromide and water. Iodic acid has an oxidation potential 

 O064 volt higher than that of an equivalent and equally acid- 

 ified bromine solution. The consideration of these oxidation 

 potentials suggested to Bugarskyf the choice of iodic acid as 

 an oxidizer for the liberation of bromine from mixtures con- 

 taining a bromide and a chloride. 



Bngarsky's method of separating the bromine from such a 

 mixture consists in adding sulphuric acid with a known amount 

 of potassium diiodate, and boiling. The bromine and the 

 iodine which are liberated in the interaction of the free acids, 

 according to the equation 



2HI0 2 + lOHBr = 5 Br, + I 2 + 6H,0, 



escape from the solution and may be collected in the distillate. 

 These free halogens may be made the measure of the bromide 

 taken, or the amount of the bromide may be calculated from 

 the amount of the iodic acid remaining. When the liberated 

 halogens are absorbed in potassium iodide, the amount of free 

 iodine, as determined by titration, proves to be much less than 

 is to be expected from the equation above, and Bugarsky, con- 

 vinced that the results are much more nearly in accord with 

 the theory when the excess of the iodic acid remaining is 

 made the measure of the reaction, prefers, therefore, to esti- 

 mate the bromide by determining in an aliquot portion of the 

 boiled solution the iodate which remains, and to determine the 

 chloride in another aliquot portion of the solution by Yolhard's 

 process of titration with standard sulphocyanate. 



The difference in the results of these two methods of deter- 

 mination Bugarsky attributes to loss of free bromine by the 

 action of steam, in consequence of which hydrobromic acid is 

 formed and oxygen set free, as in the equation 



2H 2 + 2Br, = 4HBr + O a . 



But Andrews points out that hydrobromic acid thus formed, if 

 returned with the condensed steam to the liquid, must be reox- 



*Zeitsehr. phys. Chem., x, 405. 

 fZeitschr. anorg. Chem., x, 387. 



Am. Jour. Sci.— Fourth Series, Vol. XXXIV, No. 203.— November, 1912. 

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