igo

METHOD OF OBTAINING SILEX.

Rationale. ..The acid added to the solution of flint unites tothe potash, and forms sulphate or muriate of potash; the siliceousearth is therefore precipitated.

Remark. ..It is necessary to add excess of acid, in order thatall the foreign earths which are present may be separated.

If the solution of flints be diluted with a great quantity ofwater, as for instance, in the proportion of 24 parts to one, andin this state an acid be poured upon it, no perceptible precipita-tion will ensue; the silex continues suspended in the fluid, andis invisible on account of its transparency; but it may be madeto appear by evaporating part of the water.

The solution of flint, on account of its affinity with the car-bonic acid is also in course of time decomposed by mere contactwith air.

Another method of obtaining silex exceedingly pure is to se-parate it from fluoric acid. We shall notice this process intreating of that acid. »