HYDROFLUORIC ACID. 213 



process. This gas is so poisonous, when inhaled, and 

 its solution so corrosive to the skin, that its prepara- 

 tion, in any considerable quantity, should be left to the 

 experienced chemist. 



Explain the ^28. EXPLANATION. In the above pro- 



process ? cess, the fluor spar, which is a fluoride of 



calcium, furnishes the fluorine, and hydrated sulphuric 

 acid, the hydrogen. The remaining constituents unite 

 to form sulphate of lime, which remains in solution. 



529. ETCHING ON GLASS. It has already 

 cess for etch- been stated that hydrofluoric acid attacks 

 wg glass. glass, and many minerals. By covering 

 with wax, they may be protected against the corrosion. 

 Advantage is taken of these two facts in etching 

 upon glass. The surface is first slight- 

 ly warmed and rubbed with beeswax, 

 and then warmed again, to produce an 

 even coating. Figures, or letters, are 

 then drawn upon the glass, through the wax, with 

 a pen-knife, or other pointed instrument. The plate, 

 being now exposed for a few minutes, to the fumes 

 of hydrofluoric acid, and the wax subsequently re- 

 moved, is found to be deeply etched. Fumes of hy- 

 drofluoric acid, for the purpose, are best obtained by 

 placing a half tea-spoonful of pulverized fluor spar, 

 in a warm tea-cup, and covering the powder with oil 

 of vitriol. A little ether, or potash, will be found of 

 use in removing the last portions of wax from the 

 plate. 



Explain the 530. EXPLANATION. As OXygeil COm- 



above process, bines with carbon to form carbonic acid, so 



