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-Jluorie 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 siUceo-fiu- 

 oric acid. This was formerly called Jluoric 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 

 the Jiuoric, 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 Jluates with the alkalies and 

 salifiable earths. 



It also unites to borax, 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 JiuO'borates. 



ALKALIES. 



Alkalies are an important class of bodies. They 

 have received this name because one of them, 



