359 
on different Combinations of Fluoric Acids . 
some sulphuric acid in consequence of the high temperature 
employed in making the gas was volatilized, and mixed with the 
subsilicated fluoric acid, and that mercury also was present 
from the acid being prepared over this metal. 
These experiments too oppose another statement relative to 
a method prescribed for making fluoric acid gas free from silex, 
by merely heating strong subsilicated fluoric acid in a retort, 
and collecting the gas over mercury. It is asserted, in chemi- 
cal works of some reputation, that this process is successful. 
I have never found it so, having always obtained results similar 
to those above stated. This, I suppose, is one of the many 
errors that have secretly crept into repute, and has been be- 
lieved, because never subjected to the test of experiment. 
The action of concentrated sulphuric acid on subsilicated 
fluoric acid, is similar to that of muriatic acid gas, occasioning 
a disengagement of silicated fluoric acid gas. Facts which 
appear to prove, that water is absolutely essential to the exist- 
ence of this acid. 
Boracic acid decomposes it, in a very different way, not from 
any predominant affinity for the water, but in consequence of 
a stronger attraction for the fluoric acid itself. Silicated fluoric 
acid of course is not produced ; but liquid fluoboracic acid and 
the silex is precipitated in a gelatinous state, as when ammonia 
is employed. 
These are the principal facts I have to notice respecting this 
acid. Before I conclude, I shall briefly mention a few other 
circumstances. Applied to the tongue, in its concentrated state, 
it produces a very painful sensation, like that which strong 
muriatic acid does, and it has a very similar effect on the 
cuticle. It does not appear to erode glass, for I have kept it in 
3 A a 
