Oooch and Osborne — Potassium Aluminium Sulphate. 171 



of the equivalent of the acidic ion. In experiment (2) the 

 bromide was increased tenfold and in experiment (3) the 

 bromate tenfold with similar though incomplete effects. In 

 experiment (4), in which both the bromide and the bromate 

 amount to ten times the theoretical equivalent of the acidic 

 ion, the results show a liberation of bromine somewhat in 

 excess of the five-sixths proportion. In experiments (5) (6) (7) 

 further increase in the amounts of bromide and bromate and 

 in the time of boiling advanced the reaction so that amounts 

 of bromine were liberated considerably in excess of the five- 

 sixths proportion. These results seem to indicate that the 

 deficient hydrolytic effect is advanced by large increase in the 

 proportions of either the bromide or the bromate or both, and 

 would seem to confirm the natural inference that the products 

 of the action of the bromide and the bromate upon aluminium 

 sulphate take part essentially in the hydrolytic action as well 

 as the sulphate itself. These products naturally increase 

 with the concentration of the reacting substances. With a 

 very large increase in the amounts of the bromide and bro- 

 mate and prolonged boiling, it would be natural to expect the 

 completion of the hydrolysis to the point of liberating bromine 

 equivalent to the entire amount of the acidic ion. 



Experimental difficulties such as the necessity and difficulty 

 of supplying water frequently during the boiling, the periodical 

 titration of the iodine liberated in the receiver, made of doubt- 

 ful value experiments extended over many hours. When, 

 however, the residue left in the Voit flask in experiment (7) 

 was treated with a mixture of 1 grm. of potassium iodide and 

 0'5 grm. of potassium iodate, the iodine set free on boiling for 

 an hour longer indicated that the acidic ion had been very 

 nearly liberated. 



The iodine-iodate mixture is extremely sensitive to the action 

 of small amounts of free acid. Experiment showed that the 

 bromide-bromate mixture is also a very delicate indicator of 

 free acid ; 0'00018 grm. of sulphuric acid proving to be suffi- 

 cient to liberate bromine from the bromide-bromate mixture 

 when boiled in the Voit flask under the experimental conditions. 



That the progress of the hydrolytic reaction is so much more 

 rapid in the case of the iodide and iodate is apparently due to 

 the specific action of these substances upon the basic aluminium 

 sulphate rather than to a more exact removal of the free acid. 



It will be recalled in this connection that, as Moody has 

 shown,* the iodide-iodate mixture, taken in moderate amount, 

 does not further hydrolyze the basic salt produced in the action 



* Moody, this Journal, xxii, 184, 1906. 



