on different Gbmlinations of Fluoric Add. 379 



fluoric acid, that had distilled over, was condensed in the 

 colder part ot the neck, and was absorbed by bihulous 

 paper, previouslv introduced to prevent the distilled fluid 

 from entering the jar lor the reception oF the g:as. When 

 the whole oh the acid in the bulb of the retort had beea 

 evaporated; little or no siUx remained. 



The general result ot this experiment is very duTerent 

 from that which Dr. Priestley, who first made it, obtained. 

 Instead of silicated lluoiic acid gas, he procured '^ vitriolic 

 acid air," sulphureous acid gas. 



1 have tried al^o the effect of heat on the siliceous crust, 

 formed by the decotnposition of silicated fluoric acid gas, 

 by wilier : but could ob;ain no sulphureous acid gas, as 

 Dr, Priestley did only a small quantity of silicated fluoric. 



The c<;rrt;ctniss of Dr. Priestley's observations cannot bs 

 doubled. 1 can onlv account f(<r his results, bv supposing 

 that sonje sulphuric acid in consequence of the high tem- 

 perature eniploved in makingf the gas was volatilized, and 

 mixed with the subsilicaied fluoric acid, and that n)ercuryaIso 

 was present from ihe acid being prepared over this metal. 



These experiments too oppose another statement relative 

 to a nKtliod prtsciibtd for niaking fluoric acid gas free 

 from silex, by merelv heating strong suhsilicated fluoric 

 acid in a retort, and coUecliKg the gas over mercury. It 

 is asserted, in cbeujical works of some reputation, that this 

 process is successful. I have never found it so,, having 

 aKva\s obtained results similar to those above stated. This 

 1 suppose is one of the many errors that have secret Iv crept 

 into repute, and has been believed, because never subjected 

 to the test of experiment. 



The action ot concentrated sulphuric acid on subsilicuted 

 fluoric acid, is suriilar to that of nuniatic acid gas, occa- 

 s>ionin::i a disengagement of silicated fluoric acid gas. 

 Fact< which appear to prove, that water is absolutely essen- 

 tial to the existence of this acid. 



Boracic acid decomposes it, in a very different way, not 

 from any predominant affinity for the water, but in couse- 

 queuee of a stronger attraction lor the fluoric acid itself. 

 Silicated fluoric acid of course is not produced ; but liquid 

 fluoboracic acid and the silex is precipitated m a gelatinous 

 Stare, as when ammonia is employed. 



These are the few ijrneipal facts I h^vc to notice respcct- 

 jpil this acid, lieiore I conclude, I shall briefly irieiUion a 

 few other cucnm.-itances. Applied to the tongue, in its cou- 

 cculralcd state, it producer a very paintui sensation, like 



ltia( 



