1824.] some Compounds of Fluorine. 103 



d. A cylinder of platina foil introduced into the mouth of the 

 glass tube, to prevent its being softened and closed by the 

 flame. 



e. A platina wire, at the end of which is cemented with clay 

 the subject of trial. 



I formerly suggested that topaz might be a compound of sili 

 cate of alumina, and of fluate of alumina.* I am now con- 

 vinced that no oxygen exists in it ; but that it is a combination 

 of the fluorides of silicium and aluminum. 



This system produces a considerable alteration in the propor- 

 tions of its elements. 



The mean of the six analyses quoted by M. Haiiy, in the 

 second edition of his Mineralogy, is 



Silica 36*0 



Alumina 52'3 



Fluoric acid 9"7 



98-0 



Deducting the oxygen from the metals, we have 



Silicium 18*0 



Aluminium 27'7 



Fluorine 52-3 



S8-U 

 Kri/olite. 



It has been observed to diminish in fusibility during fusion,f 

 and it was in every respect probable, from what had been seen 

 with the foregoing bodies, that it would be decomposed in the 

 fire. After being kept some time melted, it afforded an alkaline 

 solution, which, by exposure to the air, became carbonate of 

 soda, effloresced, effervesced with nitric acid, and produced 

 crystals of nitrate of soda. 



Fused on the platina plate at the mouth of the tube, a copious 

 deposit of silex collected in the tube ; and the bit of logwood 

 paper became very yellow. 



Kryolite heated in sulphuric acid on glass destroyed its 

 polish. 



1. These experiments render it highly probable that fluorine 

 will be expelled from every compound of it by the agency of fire ; 

 and consequently that we are now in possession of a general 

 method of discovering its presence in bodies. In cases where 

 a matter is infusible, and parts with it with great difficulty, as in 



* Philosophical Transactions for 1811. 

 t Hatty's Mineralogy. 



