The Peruvian and Chilian deposits are practically inexhaustible, sending out about 300,000 tons of commercial filtrate per annum. Probably the plant and apparatus now established could readily double the produce if desimble. The price varies very much with the state of the freight market, and with a constantly renewed threateuing on the part of the Peruvian Government to impose a heavy duty upon• the trade. At the present time the market valve is about 131. per ton. England and France are the largest consumers of nitrate, taking about one half the total production.
The uses of this salt are many and important. From it is made the bulk of nitric acid, being preferred to nitrate of potash on the score of cheapness, and because it produces about 7 per cent. more nitric acid weight for weight-60 as against 53. To some small extent sodium nitrate takegthe place of potassium nitrate in the manufacture of explosives, but on account of its hygroscopic propensity and slow deflagration it forms but a poor substitute for the more energetic potassium salt. It is very extensively employed as a fertilizer, and in the artificial preparation of nitrate of potassium by decomposition with chloride of potassium in the manner described 'elsewhere. Perhaps the greater part of the salt is consumed by the manufacturers of sulphuric acid in the " potting" operation. Finally, it enters to some small extent into certain medicinal preparations. It may be mentioned that as a manure the virtue of nitrate of sodium lies in the nitrogen, of which about 15 per cent. is contained in good samples. It is principally used as a top dressing to grasses and young corn.
_Phosphates of Sodium.—Several compounds of phosphoric acid and sodium are known. The principal are the subphosphate, the neutral phosphate, the pyrophosphate, and the metaphosphate, The first has as a formula, with a crystal density of 1.618. It is prepared from the neutral phosphate by adding caustic soda in excess to its solution, until a soapy feeling is apparent. The crystals effloresce in the air, are soluble in 5 parts of water at 15.4°, and melt in their own water of crystallization at a higher temperature. The salt is not of much importance.
The neutral phosphate is the best known compound of phosphoric acid and sodium. From it the other phosphates are made, and it enters into a variety of medicinal preparations. Its formula is Specific gravity of the crystals 1.525; of the anhydrous salt, P619. Phosphate of soda forms large colourless transparent crystals, which effloresce in the air, and are soluble in 4 parts of cold water. They fuse in their own water of crystallization at 37°. The solution has a faintly alkaline reaction. The best method of preparation is to treat powdered bone ash with about four-fifths its weight of dilute sulphuric acid, and neutralize with sodium carbonate until a faint alkaline reaction is visible. The solution is then concentrated, the
insoluble phosphate of calcium settled out, and the clear liquor run into suitable vessels to cool and crystallize.
The pyrophosphate of sodium — specific gravity and the metaphosphate of no interest outside of the laboratory.
What is commonly called "microcosmic salt," a phosphate of soda and ammonia, is used to some considerable extent in laboratory operations as a flux. It crystallizes in large transparent prisms, which are efflorescent in dry air, and is prepared by mixing 2 parts of water, 1 part of ammonium chloride, and 7 parts of the neutral phosphate. Chloride of sodium is deposited, and the clear solution is drawn off, concentrated, and crystallized.
Silicate of Sodium.—The soluble silicates, both of potash and soda, are of considerable import ance in the arts and manufactures. They are all more or less soluble in boiling water, and when heated pass through a peculiar viscous stage before liquefying. Fused with other silicates of the earths or metallic oxides they impart this viscidity, also their transparency, and destroy all tendency to crystallization upon cooling. To these properties the transparency, and ductility of glass when cooling, are due.
The silicates arc prepared by igniting sand, or any other convenient form of silica, with caustic potash or soda, or with the carbonates or nitrates of these bases which contain volatile acids. A monosilicate is produced by fusing 1 part of silica with 24 parts of potassium carbonate. The product deliquesces in the air, and is readily soluble in water. Treated with hydrochloric or nitric acid, the monosilicate parts with a portion of its silica in gelatinous flakes. What is commonly called "soluble glass" is a silicate with the formula This was the original silicate of Fuchs of Munich, who first published in the year 1825 a paper describing the preparation of various silicates of potassium and sodium, and the applications thereof. Soluble glass is prepared by melt ing together 8 parts of sodium carbonate, or 10 parts of purified pearl-ash, with 15 parts of pul verized quartz and 1 part of powdered charcoal. A black glass is obtained, after heating for five or six hours, which is cooled, pulverized, and boiled to dissolution with five or six times its weight of water for about three hours. The boiling is continued until a specific gravity of is obtained. A voluminous gelatinous precipitate is produced—consisting of "water glass "—by adding to the solution ammonia, nitrate of sodium, and many other salts. Soluble glass is largely employed in fixing and preserving fresco colours, in the manufacture of various earthenwares, and in the preser vation and preparation of stone. This last purpose, however—the production of artificial stone— has not been a success, on account of its high cost.