CHAR XV. 



OF THE ATOMIC WEIGHT OF FLUORIC ACID 

 AND ITS COMPOUNDS. 



THE investigation of the atomic weight of fluo* 

 ric acid is attended with particular difficulties, 

 owing to the great tendency which it has to 

 combine with silica. The fluor spar employed 

 for procuring it is seldom quite free from silica ; 

 but the specimens selected, in order to procure 

 the acid for investigation, must be quite pure. 

 The spar must be reduced to powder, mixed 

 with sulphuric acid, and heated in metallic ves- 

 sels, and the fluoric acid must be received in 

 a metallic vessel ; for if the acid come in con- 

 tact with glass it is instantly converted into 

 fluosilicic acid. I employed a leaden alembic 

 and receiver for preparing the acid ; but I find 

 that it cannot be kept in a leaden vessel for any 

 length of time, for the lead is soon corroded, 

 and an insoluble fluate of lead formed. Vessels 

 of silver answer very well for keeping it, pro- 

 vided the stopper be air tight ; for it is so vol- 

 atile as not to be easily confined. I put a vessel 

 containing it upon a shelf in a press, where I 

 keep my collection of acids in glass phials ; on 

 opening the press door some days after, I was 

 surprised to observe all the phials quite opaque, 



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