RICHARDS AND STULL. — BROxMIiNB AND OXALIC ACID. 335 



Figure 3. 



Air was drawn through the solutions, and tlie liberated iodine in B and E 

 titrated with thiosulphate. Free iodine, equivalent to 22.80 c.c. j"^- thio- 

 sulphate, was found in bottle B, while the acid solution of bromine, D, 

 had given up to E only the equivalent of 2.50 c.c. of j'^ thiosulphate. 

 No iodine was set free in C or F. This experiment was repeated, letting 

 the air first pass through the bromine solution containing hydrobromic 

 acid and then through the aqueous solution of pure bromine. The 

 bromine containing tlie acid lost bromine equivalent to 2.10 c.c. of 

 thiosulphate j\j, while the solution free from acid lost the equivalent of 

 21.00 c.c. The strength of the hydrobromic acid was about five per cent. 

 It is evident from this that hydrobromic acid in some way combines with 

 bromine. A solution of potassium bromide was found to act in the 

 same way. 



Similar results have been attained by Jakovkin * by studying the 

 distribution of bromine between carbon disulphide and solutions of bro- 

 mides, lie found that even chlorides in solution possess a slight, 

 although far less marked tendency to diminish the reacting tendency of 

 bromine, while the effect of bromides is very great. 



This effect must be due, of course, to the formation of tribromides in 

 solution, and there is good reason to believe that these are about as 

 highly ionized as the bromides from which they are formed. Hence the 

 retarding action of hydrobromic acid may be supposed to be due chiefly 

 to the tendency of the bromide ion to add bromine, and thus to remove 

 this bromine from the field of action. 



The essential details of the action of bromine on oxalic acid may 

 therefore be supposed to take place in accordance with the following 

 scheme, in which tiie main reaction under investigation is underlined. 



* Zeitschr. pliys. Chem. 20, 19 (1H9G). 



