On the Identity of S ilex and Oxygen. 359 



vessel. But, what were these crystals? They were pure silex, 

 aod had deserted this very acid, which, in all other cases, 

 would have seized on it and dragged it into even aeriform 

 existence. The native fluate of lime is so very generally con- 

 taminated with silex, if this expression may be allowed, 

 that it is probable no fluoric acid exists without some of this 

 ingredient; it may indeed owe its origin to this body, so 

 uniformly are they associated. 



But, that singular influence of fluoric ^cid upon silex, 

 the corrosion of glass, is what has been chiefly noticed by 

 most authors, for it does not appear that a direct application 

 to the mere silex has yet been attempted, at least, with thai 

 precision which might have obtained a satisfactory result. 

 T-hat this acid should prefer the silex to the alkali, and in 

 a case of single elective attraction too, is contrary to every 

 table that has yet been published, and hence, in this ex- 

 ample at least, it forms an exception to the general rule. 

 But if, in similar experiments, the acid selects the silex from 

 lime, a substance which is placed at the top of the list, in all 

 arrangements, how much further does this error extend? 

 Though in making experiments with this very curious li- 

 quid I have employed various species of glass, ^principally 

 with a view to improve this method of etching, I have 

 generally preferred plate- glass, on account of its form, con- 

 venience, and greater capability to endure the necessary 

 pressure, so as to secure a number of perfect impressions. 

 This glass is always, without exception, composed of 

 lime, silex, alkali, and, occasionally, some other ingredients 

 of less consequence in the present question. 



It is astonishing, that in all the accounts of the decom- 

 position of glass by fluoric acid, and even by other means 

 of still greater energy, by electricity, little notice has been 

 taken of the oxide of lead, and the subseqient disposition 

 of the whole of the ingredients. I make no doubt, that 

 flint-glass has been more frequently employed than any 

 other, but I do not find that silex has ever put on that pe- 

 culiar character of an earth, an alkali, or a salifiable base, 

 ajid attached itself to the negative pole. On this subject, I 

 confess, I feel extremely solicitous, as, in the late very 



Z 4 splendid 



