Contractions. - Silic. Sil.
Present name. - Silicic Anhydride. SiO2.
Pure Flint, Silex. For. name: German, Kieselerde.
Hahnemann directs this to be prepared as follows: -
"Take half an ounce of mountain-crystal and expose it several times to a red heat, or take pure white sand and wash it with distilled vinegar; when washed mix it with 2 ounces of powdered Natrum, melt the whole in an iron crucible until effervescence has ceased and the liquefied mass looks clear and smooth, which is then to be poured upon a marble plate. The limpid glass which is thus obtained is to be pulverized while warm and to be filled in a phial, adding four times its own weight of distilled water (the phial being exactly filled to a level and a stopper being put in immediately). This mixture forms a solution which remains always clear; but upon pouring it into an open phial, which is loosely covered with paper, it becomes decomposed, and the snow-white Silica separates from the Natrum and falls to the bottom of the phial."
The following process, which does not differ in any essential particular from that of Hahnemann, is practically the better one: -
Silica, in powder ....
Dried Carbonate of Sodium. .. ..
Fuse the 4 parts of dry Sodic Carbonate in a clay crucible, and then gradually add to the fused mass the powdered Silica; at each addition of which an escape of carbonic acid gas takes place, so that a roomy crucible should be used.
When the carbonic acid gas is no longer given off, pour the fused mass upon a clean marble slab, and when it is slightly warm pulverize in a mortar into small pieces, put into a wide-mouthed bottle, and add sufficient distilled water to dissolve it, the stopper being capped with wet bladder. The following day the solution may be diluted and rapidly filtered through cotton wool to purify from small pieces of dirt, &c; then add to the filtered liquor Hydrochloric Acid in small quantities from time to time. The hydrated Silica is precipitated in the form of a bulky gelatinous white precipitate, which is collected and washed with distilled water upon a square frame filter. The washing must be continued until the filtrate neither tastes nor precipitates solution of Nitrate of Silver. The precipitate, when thoroughly washed, may be advantageously dried upon a porcelain water-bath, when it shrinks to an impalpable powder, which has no taste.
The discovery of dialysis by the late Prof. Graham has supplied a method by which a moderately strong solution of pure Hydrated Silica may be obtained. It is, however, more interesting than useful, as it will not keep, the Silica becoming solid after a few days.
Reference to Horn. Proving. - Chr. Kr., v.