HYDROFLUORIC ACID. 395 



tube. Having obtained a gas, supposed to be fluorine, which 

 did not act upon glass, mixed with much oxygen, he substituted 

 for this, another operation quite analogous to the usual process 

 for chlorine. Oil of vitriol was heated upon a mixture of fluor 

 spar and peroxide of manganese, in a glass retort. The gaseous 

 product was believed to be a mixture of hydrofluoric and fluosi- 

 licic acids with fluorine vapour, which were not separated from 

 each other, but the latter is described as a gas of a yellowish 

 brown colour, having an odour resembling chlorine and burnt 

 sugar, and capable of bleaching. Fluorine did not act upon 

 glass, but combined at once with gold. The Messrs. Knox 

 have obtained similar results.* But more than one skillful 

 chemist of name has been less fortunate in obtaining indications 

 so decisive of the isolation of fluorine. 



Hydrofluoric acid, H F. Schwankhardt, of Nuremberg, ob- 

 served in 16/0, that it was possible to etch upon glass by means 

 of fluor spar and sulphuric acid, but it was not till 1771 that 

 Scheele referred this action to a particular acid which sulphuric 

 acid disengaged from fluor spar. Wenzel first obtained the true 

 hydrofluoric acid, exempt from silica, by preparing it in proper 

 metallic vessels, the acid collected by Scheele being the fluosi- 

 licic and not the hydrofluoric. The preparation and properties 

 of the pure acid were more fully studied by Gay-Lussac and 

 Thenard in 1810. It was then known as fluoric acid, and was 

 supposed, according to the doctrine of the day, to contain oxy- 

 gen. The idea of its being a hydrogen acid was first suggested, 

 a few years afterwards, by M. Ampere, whose views in theore- 

 tical chemistry were often marked by much acuteness and origi- 

 nality. The view of Ampere is now generally assented to, al- 

 though from our imperfect knowledge of fluorine, the constitu- 

 tion of hydrofluoric acid does not rest upon the same indispu- 

 table evidence as that of hydrochloric acid, to which it is assimi- 

 lated. 



Preparation. To obtain hydrofluoric acid anhydrous, a spe- 

 cimen of fluor spar is selected free from siliceous minerals and 

 galena ; this is reduced to an impalpable powder and distilled by 

 a gentle heat in a retort of lead, with twice its weight of highly 

 concentrated oil of vitriol. The materials become viscid and 



Baudrhnont, Phil. Mag. 3rd series, v. 10, p. 149 ; G. J. and the Rev. T. 

 Knox, Ib. vols. 9, p. 107 and 12, 105. 



