326 PROCEEDINGS OF THE AMERICAN ACADEMY. 



the newly presented fact concerning the speed of the bromine-oxalic acid 

 reaction furnishes new evidence that the C 2 4 " ion is that which is attacked 

 by the bromine. The following reasoning will make this point clear. 



The two following equations represent the two possible equilibria ex- 

 isting side bv side in the oxalic solution : — 



(COO)/' + 2H- ±^ (COOH) 2 (1) 



(COO) 2 IT + H- U (COOH) 2 (2) 



If G = concentration of the ion C.,0 4 ", G\ = concentration of the 

 ion C 2 4 H' , 6 2 that of the hydrogen ion, and G 3 that of the uudissociated 

 acid, the law of " mass-action " demands the following equations of 

 equilibrium : — 



GG z * = KC s orC = ^ (3) 



a 



2 



C L a t = KQ t orC l =^ (4) 



The concentration of the singly charged oxalic ion will therefore vary 

 inversely as hydrogen concentration, while the double charged ion, 

 (COO)/', will vary in concentration inversely as the square of the hy- 

 drogen concentration. It is fair to conclude from this argument, there- 

 fore, that the repressing action due to ionized hydrogen would be vastly 

 more effective in eliminating doubly charged ions from the solution than 

 those with a single charge. Therefore we might expect a maximum 

 concentration of C 2 4 " at a moderate concentration of oxalic acid ; and 

 since such a maximum is found in the action of bromine upon the solution, 

 we may suppose this action to take place upon the group C»0 4 ". # 



III. The Effect of Foreign Substances. 



It became now a matter of interest to test the conclusions yet further 

 by adding various foreign substances capable of affecting the ionization 

 of the oxalic acid. Accordingly hydrochloric acid and sodic acetate were 

 used as means of respectively increasing and decreasing the concentration 

 of the hydrogen ion. Each of the following solutions had a volume of 

 58.3 c.c. and contained 1.496 grams of oxalic acid and 0.1375 gram of 

 bromine. Each was allowed to react for two hours, at 23°. 



* Mr. F. R. Fraprie has lately shown in this laboratory that while alkaline oxalates 

 readily reduce K 2 Ft Cl 6 to K 2 Pt Cl 4 , oxalic acid solutions free from alkali effect this 

 reduction only slowly if at all. This is evidently another case where the ion of oxalic 

 acid is the active group. 



