168 Gooch and Osborne — Potassium Aluminium Sulphate. 



sulphates of iron, chromium, cobalt, nickel, ammonium and 

 from stannic chloride. The hydrolysis of zinc sulphate under 

 similar conditions comes to an end before the acidic ion is 

 entirely liberated and when the product is one-fifth sulphate 

 and four-fifths hydroxide. 



In the work of which the present paper is an account, the 

 reaction of a mixture of potassium bromide and potassium 

 bromate upon aluminium sulphate has been studied. Assuming 

 that the acidic ion is entirely liberated from the aluminium 

 salt, the reaction should follow the equation 



2KA1(S0 4 ), + 5KBr + KBrO s + 3H„0 

 = 2 Al(OH) 3 + 4K 2 S0 4 + 3Br 2 . 



For this work a bromide-bromate solution was made up by 

 dissolving 36 grms. of potassium bromide and 10 grms. of potas- 

 sium bromate (the proportions indicated in the equation) in 

 water and making up to 500 cm3 . Pure crystallized potassium 

 alum was the aluminium salt used and this was weighed out 

 exactly in every experiment. 



The first set of experiments was made to find out whether 

 precipitation is complete when the bromide-bromate mixture 

 acts upon the aluminium salt. In every experiment a portion 

 of the alum was weighed out, dissolved in a small amount of 

 water in a beaker and a portion of the bromide-bromate solu- 

 tion was added. In experiment (1) the mixture was boiled 

 over a flame until at the end of an hour no more bromine 

 seemed to be liberated and the cooled liquid was colorless. 

 The precipitate was, so far as possible, transferred to an ash- 

 less filter paper, washed, ignited and weighed as Al 2 O s ; but to 

 get the entire amount of precipitate it was necessary to dissolve 

 from the beaker, by means of hydrochloric acid, a closely 

 adherent film of precipitate ; and from the solution the dis- 

 solved alumina was recovered by precipitation with ammonia 

 and determined separately. In experiments (2) and (3) the 

 precipitation was brought about by passing a current of steam 

 into the solution, interrupting the process to concentrate the 

 liquid by evaporation without boiling and again passing in 

 steam. 



Table I. 



KA1(S0 4 ) 2 .12H 2 Time of KBr KBr0 3 A1 2 3 A1 2 3 



taken heating taken taken taken found Error 



grms. hrs. grms. grms. grms. grms. grms. 



(1) 1-0012 1- 3-6 1- 0-1078 -1070 0'0008 — 



(2) 0-5017 2 + 2-5 2- 0'5 0-0539 -0529 0.00 10- 



(3) 0-5029 3 + 2-5 2- 0"5 0'0541 -0559 0-0018 + 



In these experiments the precipitation proved to be complete, 

 or nearly so ; though in (3) there is obvious contamination of 



