78 ALKALIES. 



than fluoric acid has, expels the latter and unites 

 itself to the lime. 



It appears, that before the researches of Gay 

 Lusac and Thenard, the pure fluoric acid had ne- 

 ver been procured ; what had been considered as 

 fluoric acid, being, in fact, a different acid, the 

 siliceo-jluoric acid. In their experiments, the leaden 

 receiver was cooled by ice, and the fluoric acid 

 condensed into a liquid form. In this state it is. 

 the most caustic substance known, corroding the 

 skin instantly, and causing dangerous sores. 



Fluoric acid combines with silica, and becomes 

 with it a permanent acid gas, called the siliceo-flu- 

 oric acid. This was formerly called fluoric acid 

 gas. It has a pungent irritating odour, will not 

 support combustion, and forms white vapours when 

 it comes in contact with the air. It corrodes glass, 

 and combines rapidly with water, forming the li- 

 quid siliceo-fluoric acid. This acid, formerly called 

 thejluoric, also acts on glass, and is very acid and 

 corrosive. In the process for making it from 

 fluor spar and sulphuric acid, a little silicious mat- 

 ter generally existed in the spar, or glass vessels, 

 that had been used; and thus the siliceo-fluoric, and 

 not the fluoric acid, had been obtained. / 



Fluoric acid forms Jiuates with the alkalies and 

 salifiable earths. 



It also unites to bocax, forming an acid called 

 the Jluo-boric acid. This does not act on glass, 

 and is not so corrosive as fluoric acid. It gives rise 

 to Jluo-borates. 



ALKALIES. 



Alkalies are an important class of bodies. They 

 have received this name because one of them, 



