Mr. J. Davy’s Account of some Experiments , &c. 353 
combinations of these acids, and of pure fluoric acid with am- 
monia ; the third to fluoboracic acid; and the fourth to its 
ammoniacal salts. 
Sect. 1. On silicated fluoric acid Gas , and subsilicated fluoric Acid. 
The facts v/hich have already been published by M M. Gay 
Lussac and Thenard and others, appear to me to be sufficient 
to prove that pure fluoric acid has not yet been obtained in 
the gaseous state, and that silex, or boracic acid, is requisite 
that it may assume this form. Were more evidences neces- 
sary, I could advance many in point. One circumstance only 
I shall mention, proving that common fluoric acid gas is per- 
fectly saturated with silex. I have preserved this gas, made 
by heating, in a glass retort, a mixture of fluor spar and sul- 
phuric acid, for several weeks over mercury in a glass receiver 
uncoated with wax, without observing the slightest erosion to 
be produced.* 
This gas, with great propriety, has lately been called sili- 
cated fluoric. Before I proceed to its analysis, I shall notice 
what method I have found the best for obtaining it. I have, 
for a considerable time, long before M. M. Gay Lussac and 
Thenard’s work was published, added to the mixture of fluor 
spar and sulphuric acid, a quantity of finely pounded glass, and 
have thus procured the gas with the greatest facility. The 
advantages of this addition are considerable. The retort is 
saved, which otherwise, in less than one operation, would be 
* The sides of the receiver indeed became obscure ; but this was not from erosion, 
but from deposition, as appeared from the transparency and polish of the glass being 
readily restored by slight friction. What the deposition was, I am ignorant of. After 
several weeks it was so trifling, as to give only a slight degree of opacity to the re- 
ceiver. 
