on the Jiuoric Compounds, 
I decomposed 20 grains of silicated fluate of ammonia by 
solution of ammonia, and I obtained 9 2 grains of silica. This 
result offers proportions very little different from those gained 
in the preceding calculations. 
I have made some direct experiments with the hopes of 
determining the proportions of oxygen in silica, but they 
have been unsuccessful ; I have ascertained, however, that it 
requires more than three parts of potassium to decompose one 
part of silica, which shews that this substance cannot contain 
much less than half its weight of oxygen. 
I have endeavoured to separate the siliceous basis in a pure 
form, with the view of making synthetical experiments on its 
nature by combustion in oxygen, and my results, though not 
perfectly satisfactory, yet seem worthy of notice, and may 
lead to more successful attempts. 
I decomposed silica by passing potassium in excess through 
it, in a heated tube of platinum : the result consisted chiefly 
of alkali containing a dark coloured powder, the basis of silica 
diffused through it. I fused the whole mass with sulphur, 
which, in combining with the dry alkali, produced ignition. I 
attempted to detach the sulphuret of potassa by water: in this 
case the dark particles separated, but during their separa- 
tion and after, they acted upon the water of the solution pro- 
ducing gas, and, in attempting to collect them by the filter, I 
failed to procure sufficient for examination, for they were 
principally converted into silica. 
I heated the substance procured in another experiment of 
this kind with hydrate of potassa ; in this case there was a 
copious effervescence, and silica appeared to be reproduced and 
dissolved by the alkali. 
K2 
