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XVIII. An Account of some Experiments on different Combina- 
tions of Fluoric Acid. By John Davy, Esq. Communicated 
by Sir Humphry Davy, Knt. LL.D. Sec. R. S. 
Read June 11, 1812. 
Introduction. 
Two years ago, I engaged, at the request of my brother, 
Sir H. Davy, in an inquiry respecting the nature of common 
fluoric acid gas. My principal object was to ascertain whether 
silex is essential to its constitution, and whether the proportion 
is constantly the same. This subject, and experiments on the 
fluoric and fluoboracic acids, occupied me for about six months. 
Since that time, the work of M. M. Gay Lussac and Thenard 
has appeared, entitled “ Recherches Physico-Chemiques/' in 
the second volume of which is an elaborate dissertation on 
fluoric acid. These philosophers, I find, have anticipated many 
of my results, and consequently very much abridged my labour 
of detail in the following pages. To repeat what is already 
known would be useless, I shall therefore confine myself to 
describe what I have observed, which appears to me yet novel, 
or different from the observations of the French chemists. 
The order which I shall pursue, will be that which I observed in 
my experiments. I shall divide what I have to advance into 
four parts. The first part will relate to the silicated fluoric 
acid gas, and to the subsilicated fluoric acid ; the second to the 
