360 Mr. J. Davy's Account of some Experiments 
bottles of this substance more than a month without any action 
being perceptible. Exposed to the air, it slowly and almost 
completely evaporates, there being only a very trifling silicious 
residue ; and when gently heated in an open vessel, it is rapidly 
dissipated in white fumes. 
Sect. ii. On the Combinations of silicated fluoric acid Gas , and 
the subsilicated Fluoric , and the fluoric Acids with Ammonia. 
M. Gay Lussac has shewn that silicated fluoric acid gas, 
like carbonic acid gas, condenses twice its volume of the vola- 
tile alkali.* The experiment I have several times repeated, 
and constantly with the same result, no difference appearing 
when the acid gas was added in great excess to the alkaline, 
or the alkaline to the acid. This being the case, and knowing 
the specific gravities of the two gasses,-f 100 parts by weight 
of silicated fluat of ammonia seem to consist of 
24.5 ammonia 
75.5 acid 
100.0 
Silicated fluat of ammonia volatilizes unaltered, if heated by a 
spirit-lamp in the vessel in which it is formed, and provided 
moisture be entirely excluded. 
Like silicated fluoric acid gas itself, this salt is decomposed 
by water, and a similar precipitation of silex occurs, and in the 
same proportion. Thus the salt formed by the union of 30 
* Vide Mem. d’Arcueil, Tom. II. 
f According to Sir H. Davy, ioo cubic inches of ammonia, barom. 30, therm. 60, 
weigh 18 grains. It is this estimate which I have taken. 
