396' FLUORINE. 



swell considerably, and an acid vapour distils over, which is 

 even more acrid and suffocating than chlorine, and produces 

 severe sores if allowed to condense upon the hands of the ope- 

 rator. This vapour is received in a flask or bottle, likewise of 

 lead, kept cold by ice, in which it condenses without the pre- 

 sence of water. The acid, thus obtained, may be preserved in 

 vessels of platinum or gold, provided with stoppers of the same 

 metal which fit accurately, or in vessels of lead formed without 

 tin solder, tin being rapidly acted upon by hydrofluoric acid. 

 If the solution of this acid in water is required, the extremity of 

 the leaden tube, from the retort, may be allowed to touch the sur- 

 face of water in a platinum crucible or capsule, by which the 

 acid vapour is readily condensed ; and the dilute acid may be 

 preserved without much contamination in a glass bottle, which 

 has been previously heated and coated internally with melted 

 bees-wax. 



Fluor spar, which is employed in this operation, is the fluo- 

 ride of calcium, upon which the action of hydrated sulphuric 

 acid is similar to its action upon chloride of sodium j in which 

 hydrochloric acid is produced. Water is decomposed, by the 

 hydrogen and oxygen of which, the fluorine and calcium are con- 

 verted respectively into hydrofluoric acid and lime ; and the 

 former comes off as vapour, while the latter remains in the retort 

 as sulphate of lime. In symbols : 



Ca F and H O, S O 3 = H F and Ca O, S O 3 . 



Water is, therefore, necessary to the formation of hydrofluoric 

 acid in the process given for its preparation ; and the observation 

 of M. Kuhlman, that anhydrous sulphuric acid vapour has no 

 action upon fluor spar at a high temperature, is readily ac- 

 counted for. Did fluor spar contain an oxygen acid, in combi- 

 nation with lime, the acid should be equally liberated by the an- 

 hydrous or hydrated sulphuric acid. 



Properties. Anhydrous hydrofluoric acid is a colourless, 

 fuming and very volatile liquid, boiling not much above 60 ; 

 and which does not freeze at 4. Its sp. gr., which is 1.0609, 

 is increased to 1.25 by the addition of a certain quantity of water, 

 for which it has an intense affinity. Hydrofluoric like hydro- 

 chloric acid, dissolves the more oxidable metals with the evolu- 

 tion of hydrogen gas. Mixed with nitric acid, it dissolves ig- 

 nited silicon and titanium, with disengagement of nitric oxide ; 



