COMPOSITION OP SULPHATES. 



155 



In a paper, which I shall have the honour of communi- 

 cating to the class, I shall make known the physical pro- 

 perties of this saline substance, as well as the means and 

 conditions requisite, to promote its crystallization. 



When I had at my disposal a certain quantity of this This sulphate 

 sulphate, it was easy for me to rind with precision the useful in ar«- 

 proportions of potash and acid, that enter into all the salts ■ 

 with base of potash. I satisfied myself also, that this 

 sulphate of alumine is a very powerful and certain test for 

 ascertaining the quantity of potash contained in vegetables, 

 either before or after incineration. On this subject I have 

 undertaken several experiments, that will complete another 

 inquiry, which I shall have the honour of submitting to the 

 class. 



To return to the analysis, or rather the synthesis, that 

 constitutes the subject of the present paper: the following 

 are the experiments I have made, to determine the re- 

 spective quantities of acid and base, that enter into the 

 composition of alum, and of the sulphate, nitrate, and 

 muriate of potash. 



Exp. 1. In 850 gr. [13129 grs*] of solution of sulphate Quantity of 



of alumine at 34° [sp. gr. 1-307], the temperature being al !* m Policed 



. , . with a given 



10° [50° F.], 1 dissolved by the assistance of heat 100 gr. of weight of sul- 



sulphate of potash. After the liquid was cooled, I obtained P h , lte of P ot " 



from it 502 gr. of very pure aliim. On evaporating the 



mother water 1 obtained 18 gr. of alum; and a second 



evaporation and crystallization produced 4 gr. more. The 



remaining liquor yielding no more crystals, 1 mixed it 



with 25 gr. of a solution of sulphate of alumine similar to 



that above, in order to find whether I had obtained all the > 



alum, that 100 gr. of sulphate of potash could produce. 



The mixture having occasioned only a slight precipitate of 



alum, 1 concluded, that the whole of the sulphate ©f 



potash had entered into the composition of the 524 gr. 



of alum obtained. 



Exp. 2. On the supposition, that sulphate of potash Quantity pra- 



contains 62 per cent of potash, 1 saturated 62 gr. of potash, uce ™ a 



• The proportions being all that is of importance, it would be 

 superfluous to reduce the rest of the quantities: but this is given, 

 to mark the quantity operated on. C. 



purified 



