174 FLUORIC ACID AND ITS COMPOUNDS. 



the analysis of it could not lead to any useful 

 result. 



SECT. II. 



OF THE ATOMIC WEIGHT OF FLUOSILICIC ACID. 



WHEN sulphuric acid is poured upon the powder 

 of fluor spar in a glass retort, or upon a mixture 

 of pounded glass and fluor spar, and heat ap- 

 plied, it is well known that a gas is extricated, 

 which was long distinguished by the name of 

 fluoric acid ; but the presence of silica, which 

 had been recognised in it from the first, has in- 

 duced modern chemists to give it the name of 

 fluosilicic acid. For by far the most accurate set 

 of experiments on this gas we are indebted to 

 Dr. Davy.* 



^ ne s P ecm%c gravity of this gas, as determined 

 by Dr. Davy, is 3 %5735. I found the specific 

 gravity 3*58313 ; but the specimen examined 

 contained a very small proportion of common 

 air. The quantity of this mixture being ascer- 

 tained and deducted, I found that the real spe- 

 cific gravity was 3 '6 ; for reasons which will ap- 

 pear immediately, I consider the true specific 

 gravity of this gas to be 3*6lli, that of air being 

 reckoned unity. Consequently, 100 cubic inches 



* Phil. Trans. 1812. p. 352. 



