COMPOSITION OP SULPHATES. J §n 



Hence I have presumed, that to make known the result of Attempts to 

 my experiments, though undertaken with other views, might ascertain this* 

 be of some advantage. In fact, finding by synthesis the 

 quantities of potash ; and of acid entering into the compo- 

 sition of sulphate of potash and having afterward ascertain- 

 ed, how much water they lose respectively in this combination ; 

 it appears to me, that the question is solved a priori. I must 

 confess, however, that some difficulties occurred at first in 

 ascertaining the quantity of water contained in potash ; dif- 

 ficulties which have afforded me an opportunity of knowing, 

 that, interesting as the experiment of Mr. Berthollet is, the 

 treatment of potash with iron filings is not a method suffici- 

 ently precise to be conclusive. My opinion on the contrary 

 was, as it still is, that the substances most proper for detect- 

 ing the water contained in potash should not be oxidable ; 

 and that their action should be confined to the separation of 

 the water contained in the potash. Among the experiments 



1 made, the following appeared to me best to fulfil the con- 

 ditions I had imposed on myself. 



Exp. 3. Twenty grammes of potash prepared in the labo- Experiment. 

 ratory of Mr. Vauquelin were carefully mixed with ]6o of 

 very pure silex, which must have been dry, as it was heated 

 for two hours in a forge fire before it was used. The mixture 

 was introduced with much caution into a glass tube about 



2 cent. [7*87 lines] in diameter. This tube, one of the ex- 

 tremities of which was closed, weighed 72 gr., and with the 

 mixture 252 ; very good weight, it is true, but this excess I 

 ascribed to moisture attracted by the potash during the tri- 

 turation. This tube I introduced into a small cylinder of 

 sheet iron, to prevent its being fused by the direct action of 

 the fire. This apparatus was subjected for an hour to the 

 action of a very moderate fire. No sooner did the mixture 

 receive the impression of the heat, than a very large quautity 

 of water reduced to vapour was suddenly expelled, and con- 

 tinued to be evolved five or six minutes, after which nothing 

 more was extricated. 



When the tube was cold, I weighed it very carefully, and 275 of water 

 found it had lost 5*5 gr. This experiment, which I repeated in l0 ° of P°*" 

 seveial times, sometimes collecting the water, constantly af- 

 forded me the same results, both with potash of my own pre- 

 paring; and with that from the laboratory of Mr. Y r auquelin ; 



whence 



