ON SOME CHEMICAL AGENCIES. OF ELECTRICITY. $7 



our experiment with nitrate of barytes, this change could 



scarcely be perceived. Hence we have still a suspicion, that 



the fluoric acid, which adheres strongly to alumine, may have 



carried oft' a portion of this earth with it at a high tempera- off^ome^lu- 4 



ture, as was observed by Mr. Klaproth in his experiments on mine with it. 



the topaz. In our experiments therefore there may have been 



a loss of both fluoric acid and alumine at the same time. 



Finally we conceive the presence of fluoric acid will explain This accounts 

 that striking emanation of bubbles, which is exhibited by 

 this stone when exposed to the flame of the blowpipe: it ap- 

 pears, that part of the acid united to its earthy base produces 

 a very fusible substance, while another is extricated in the 

 forms of vapour. This supposition is strengthened by the 

 observation of Mr. Gahn, that the topaz, particularly that of Topaz emits 

 Brasil, when exposed to a very violent heat, emits bubbles si- the same ' 

 milar to those produced on the pyropbysalite. As the topaz 

 contains alumine and silux, with a portion of fluoric acid, we its place 

 conceive it ought to be placed in a mineralogical view be- amon 8 mine- 

 tween the topaz and the pyenite, which, according to Mr. 

 Bucholz, contains 0*17 of fluoric acid*. 



XII. 



On some Chemical Agencies of Electricity, by Humphrey 

 Davy, Esq. F. R. S. M. R. /. A. 



Concluded from Vol. XVIII, p. 339. 



V. On the Passage of Acids, Alkalis, and other Substances 

 through various attracting chemical Menstrua, by Means of 

 Electricity, 



XjSlS acid and alkaline substances, during the time of their Passage of va 



electrical transfer, passed through water containing vegetable rious substan " 

 r ° & & ces through at- 



* According to Vauquelin the pyenite, schorlite of Klaproth and 

 others, schorliform beryl of some, contains but 006 of fluoric acid, 0*60 

 alumine, SO silex, 002 lime, and 0-01 water. Hauy thinks, that the 

 pyrophysalite should be considered as a variety of the topaz. Ed. 



colours 



