Gooch and Cole — Chlorine in Haloid Salts. 257 



Art. XIX. — The Use of Telluric Acid in the Determina- 

 tion of Bromine associated with Chlorine in Haloid Salts / 

 by F. A. Gooch and H. Isabellb Cole. 



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



The satisfactory separation of bromine from chlorine by the 

 action of differential oxidizers in solution upon haloid salts of 

 these elements depends upon the realization of several condi- 

 tions : First, the complete removal of free bromine from the 

 solution ; second, thorough action of the oxidizer in setting 

 free bromine, so that hydrobromic acid liberated in the action 

 may not escape unattacked ; third, the presence of a suitable 

 reducing agent (best a reduction product of the oxidizer) which 

 is effective in counteracting the tendency of free bromine to 

 act upon hydrochloric acid and water with formation of non- 

 volatile bromic acid ; and, fourth, practical inertness toward 

 free bromine on the part of everything finally remaining in 

 solution, so that the solution may be devoid of combined 

 bromine in any form when the operation is at an end. These 

 essential conditions of accuracy in the analytical process have 

 been met with a fair degree of success in a process recently 

 developed in this laboratory,* in which reaction takes place 

 between hydrobromic acid and selenic acid (or a mixture of 

 sodium selenate with sulphuric acid) used as an oxidizing 

 agent. The present paper is the account of an attempt to find 

 conditions under which a similar reaction of telluric acid with 

 hydrobromic acid may be brought to completion (any tendency 

 toward the formation of bromic acid being counteracted by 

 tellurous acid formed in the process and the reverse action of 

 bromine upon the tellurous acid practically prevented by 

 volatilization of the bromine) in accordance with the expression 



H 2 Te0 4 + 2HBr^>H 2 Te0 3 + H 2 + Br 2 , 



under such conditions that a similar reaction may not take 

 place between telluric acid and hydrochloric acid set free in 

 the reaction. 



Unlike selenic acid, telluric acid is not capable, at reasonable 

 concentrations, of ready reaction with bromides to form hydro- 

 bromic acid and then free bromine. The function of liberating 

 the hydrobromic acid in order that the telluric acid may play 

 the part of the oxidizer must devolve upon some stronger acid. 

 For this purpose we have made use of sulphuric acid at such 

 dilution that it may not by itself liberate bromine from the 

 bromide with .formation of volatile sulphur dioxide. In the 



* Gooch and Blumenthal, this Journal (4), xxxv, 54, 1913. 



Am. Jour. Sci.— Fourth Series, Vol. XXXVII, No. 219.— March, 1914. 

 19 



