Commercial silicate of sodium is in a liquid state, and should be kept in well-closed vessels, as the solution would absorb carbonic acid from the air and separate silicate. A semi-transparent, almost colorless, or yellowish, or pale greenish yellow, viscid liquid, odorless, having a sharp, saline and alkaline taste, and an alkaline reaction. The specific gravity of the commercial solution is between 1.300 and 1.400. It is employed in the manufacture of artificial mineral waters to introduce the insoluble silica. Sodium silicate is also crystallized; sodium silicate dry is its commercial name, and we advise to employ this preparation. Prepare a 10 per cent, solution by dissolving one part of the powdered sodium silicate in five parts of distilled water. Digest and agitate until dissolved. Add more distilled water (about 4 parts to make it 10 parts), sufficient to give it a specific gravity of 1.105 to 1.107 at 15° C. If the commercial liquor sodium silicate be employed, add water enough to reach the same specific gravity, when it will contain 10 per cent, of dry sodium silicate in solution. Prepare for immediate use. If a solution be kept in stock, keep air-tight. Proportion of solution 10 to 1.

Sodium Sulphide (NaS; 39 - Na2S; 78). It is prepared either by leading sulphuretted hydrogen in a solution of caustic soda, when crystals of sodium sulphide will separate in the cold, or sulphuret of potassium (liver of sulphur), substituting soda for potash. Sublimed sulphur one part; carbonate of sodium two parts. Rub the carbonate of sodium, pre viously dried, with the sulphur, and heat the mixture gradually in a covered crucible until it ceases to swell and is completely melted. Then pour the liquid on a marble slab, and when it has solidified and become cold, break it into pieces, and keep them in a well-stopped bottle. It is partly deliquescent on exposure, and yields with water a brownish-yellow solution which has a strong odor (suggesting that of rotten eggs) of sulphuretted hydrogen, and evolves the latter freely on the addition of hydrochloric or sulphuric acid, sulphur being at the same time deposited. If not protected from contact with air, the solution will be oxidized. This compound or its solution is used in the manufacture of artificial mineral waters for "sulphur waters" the same as acid hydrosulphuric. It is never put in the apparatus, but gauged into each bottle, or the required dose separately put up in vials for each bottle, and mixed for immediate consumption; or, a separate fountain for sulphur waters exclusively is employed.