Royal Society. 73 
eonfirms the theory that considers azote and chlorine as yet 
undecompounded—or that, if these substances are com- 
pounds, their elements are unknown, and have never been 
obtained separate, 
July 8. A paper from Sir Humphry Davy was communi- 
eated by the President, on the principle existing in the fluorie 
compounds, or the fluoric principle. There are detailed in it 
many new facts on the substances obtained from fluor spar, 
The pure fluoric acid is very little heavier than water, but 
has its specific gravity greatly increased by its combination 
with water. 
A principle highly energetic which combines with all 
the metals and decomposes oxides, is expelled from certain 
fluates by chlorine; but from its intense powers of attrac- 
tion it fas not been yet obtained in a separate form. 
From the general series of facts, it is concluded that the 
fluoric combinations probably contain a peculiar principle 
analogous to oxygen and chlorine, that the number repre- 
senting it is less than half that of chlorine, that it is attracted 
in Voltaic experiments to the positive surface..,..that its 
acidifying powers are stronger than those of oxygen and 
chlorine, and that it communicates to its compounds lower 
refractive powers. 
Pure liquid fluoric acid the author considers as this prin- 
ciple combined with hydrogen; fluoboric gas as this prin- 
ciple combined with borax ; and silicated fluoric acid gas_as 
this principle united to silicum. 
The author, for some of the views which led to his experi- 
ments, acknowledges bis obligations to M. Aufrere. 
A paper, by Alexander Marcet, M.D. F.R.S., on the 
intense degree of cold which is produced by the evaporation 
of the sulphuret of carbon, was read. 
This liquor appears, from the author’s experiments, to be 
the most evaporable of all known fluids, or at least to pro- 
duce by its evaporation the most intense degree of cold. 
If the bulb of a spirit thermometer, closely enveloped in 
fine flannel or cotton wool, be moistened with the fluid, 
its temperature falls to about 0; but if the thermometer be 
exposed to the effect of a vacuum by being inclosed in the 
receiver of a good air pump, it sinks to —S0° in one or two 
minytes. The congelation of mercury in glass tubes may 
therefore be most quickly and easily performed by this pro- 
cess at all seasons and under any atmospheric temperature. 
A short paper by Mr. Smithson was read, containing an 
a¢count of a substance ejected from Vesuvius about 1792, 
auc called, in 1794, vitriolated tartar. This substance has 
never 
