Cole — Iodine and Bromine in Haloid Salts. 265 



Art. XX. — The Estimation of Iodine and Bromine in 

 Haloid Salts oy Means of Telluric Acid', by Harriet 

 Isabelle Cole. 



[Contributions from the Kent Chemical Laboratory of Yale University — cclxi. J 



It has been shown in a previous paper* from this laboratory 

 that telluric acid may be used as an oxidizing agent to liberate 

 bromine from hydrobromic acid and that the method may be 

 relied upon to determine with accuracy amounts of bromine 

 up to 0*3 grm. associated with 0*25 grm. of chlorine combined 

 in the form of chloride. The present paper is the account of 

 an attempt to extend this process to the estimation of iodine 

 by finding the conditions under which telluric acid will react, 

 first, with hydriodic acid to liberate the iodine quantitatively 

 without a similar liberation of bromine, and second, with 

 hydrobromic acid in such a way as to bring the reaction to com- 

 pletion without setting free chlorine from the hydrochloric acid 

 formed in the reaction. 



Telluric acid is not capable alone of bringing to completion 

 the reaction with iodides to form hydriodic acid and then free 

 iodine in solution, at such dilution that it will not also liberate 

 some bromine from the bromide. The function of liberating 

 the hydriodic acid so that the telluric acid may act as oxidizer 

 has been performed by a very dilute solution of sulphuric acid, 

 which after the removal of the iodine is then increased in order 

 that the bromine of the hydrobromic acid may be similarly set 

 free. 



In the work to be described the telluric acid was pre- 

 pared directly from the dioxide by precipitating tellurons acid 

 from a hot solution of tetrachloride by means of water, and 

 oxidizing with chlorine to telluric acid. Selenium present in 

 the material may be removed by evaporating the telluric acid 

 solution on a water bath. A slight reduction takes place in 

 the presence of strong hydrochloric acid at this temperature 

 and the selenium is first thrown out, the reduction being 

 hastened by the presence of metallic tellurium. The filtered 

 solution is re-chlorinated and evaporated in a current of air at 

 room temperature. The telluric acid is washed with strong 

 alcohol to remove traces of hydrochloric acid and recrystallized 

 two or more times from water solution. In this way a very 

 pure product maybe readily prepared in considerable quantity. 



The potassium bromide used was made by ignition and 

 thorough fusion of potassium bromate specially prepared from 

 purified bromine and potassium hydroxide. The potassium 

 chloride was made by recrystallizing five times and thoroughly 

 igniting pure potassium chlorate. The potassium iodide was 

 prepared with great care, by acting with re-sublimed 

 iodine upon iron wire, three-fourths of the iodine being 

 * Gooch and Cole, this Journal (4), xxxvii, 219, 1914. 



