55(5 COMPOSITION OF SULPHATES. 



given weight of purified with alcohol, with 48 gr. of sulphuric acid at 6(f 

 potash and of^ S p # «, r- i»848], I then mixed this sulphate with 850 gr. 

 toLpfauncacid. of soluti0n of su i p hate of alumine at 34°, and conducted 

 the rest of the process as in the preceding experiment. 



But what was my surprise, when, on adding together 

 all the alum produced, I found but 408 gr., instead of 

 524, which the former experiment had yielded. The 

 comparative results of these two experiments, which I 

 •varied with quantites alternately greater and less of 

 sulphate of potash and sulphate of alumine, demonstrated 

 to me, that the proportions of potash and acid contained 

 in the sulphate of potash were very different from those 

 hitherto laid down. In fact, knowing how much alum is 

 produced by 100 gr. of sulphate of potash, and how much 

 may be obtained with a given quantity of potash saturated 

 afterward with acid, it was ensy for me, on comparing 

 the results of these two experiments, to ascertain by cal- 

 culation the respective proportions of acid and base, that 

 enter into the composition both of sulphate of potash and 

 of alum. 

 Proportions of For example, since with 100 gr. of sulphate of potash I ob- 

 *cid and base ta j <j 524 f alum; and on the other hand, 62 gr. of pot- 

 »a sufphate of - & ,;..-■ . ° 



jpotash. ash gave but 408; 1 necessarily concluded, that the potash 



contained in 100 parts of sulphate of potash must make four 

 fifths of its weight. But reflecting, that, on the one hand, 

 this quantity of potash was much greater, than is generally 

 admitted in the sulphate of potash ; and, on the other, that 

 the acid could not lose two thirds of its weight in this cora- 

 Watprm bination: I could not but suspect, that the potash contri- 

 buted to this loss in a certain proportion, and hence sought 

 some means of ascertaining the quantity of water it might 

 contain, Accordingly I made a great number of experi- 

 ments with this view, and with the result of which I have so 

 much the more reason to be satisfied, as the question to be 

 solved is very important ; since even at present, while it is 

 allowed, that potash purified by alcohol contains water, the 

 quantity is not agreed on : for Mr. Berthollet, according to 

 recent experiments, admits only 15 per cent, while Mr. Dar- 

 cet finds twice this quantity by his*. 



* Sec J own. vol, XXVII, p. 31. 



Hen ce 



potash 



