A double water glass, consisting of a mixture of potash and soda silicates, has received some considerable application. It is prepared by fusing together 100 parts of quartz and 121 parts of Rochelle salt ; or a mixture of quartz, nitre, and saltpetre; or, again, 100 parts of quartz, 28 parts of pearl-ash, 22 of carbonate of sodium, and 6 of powdered charcoal.
Tbo silicates of sodium have been employed to a considerable extent as a dung substitute, in dyeing and printing. For this purpose the solution should be as neutral as possible. They have also been used to fix ultramarine blue and other pigments. The colour is well ground up with the silicate solution at about 90 Tw., and printed without any thickening.
Stannale Sodium. Formula, by dissolving stannic acid in soda lye ; this salt crystallizes out from the solution on heating. It is less soluble in warm than in cold water, 100 parts of water dissolving 67'4 parts of the salt at 0°, and 61.3 parts at 20°. There are several methods of preparation, the beat being that invented by Young. Native peroxide of tin is pulverized and fused with a solution of caustic soda. The mixture is thoroughly agitated, and a temperature of 516° (600° F.) kept up, the tin, or oxide of tin, combining gi adually with the soda. When it is judged that the operation is complete, the contents of the pot are baled out into another vessel, cooled, broken up, and dissolved in water. The iron and other foreign metals being insoluble in the alkali readily settle out, and a clear solution of pure stannate is obtained. This may be used in the state of solution, or evaporated to dryness, or concentrated and crystallized.
Another method of preparation is to heat 22 lb. of caustic soda in an iron crucible to a low red heat, then add 8 lb. of sodium nitrate and 4 lb. of common salt. When the whole is fluxed, 10 lb. of block.tin are introduced, and the mixture kept well agitated. It soon assumes a dark colour and thick consistency, with free evolution of ammonia—from partial decomposition of the water of the caustic soda and of the nitrate. Finally, the mass becomes red-hot. It is then baled out, cooled, broken up, and treated in the manner already described.
A third method is to fuse tin ore with 1 time its weight of sodium nitrate, and pass a current of steam over the mixture, which is kept in constant agitation. Nitric and nitrous fumes are given
off and condensed. The stannate left in the pot is treated as before described. If chloride of sodium be substituted for the nitrate, hydrochloric acid is obtained as a bye product.
Haeffely's process for the production of sodium stannate may be finally noticed. Labarge (80 lb.), or red lead (54 lb.), is heated in nn iron pot with about 45 lb. of 70° caustic soda in solu tion, and sufficient water or weak washings added to hold the stannate when formed in solution. Plumbate of lead is first produced, and in this is suspended 16 lb. of feather block tin. The lend precipitates presently as a spongy metallic mass, and stannate of soda remains in solution. When all the tin is dissolved, the contents of tho pot are transferred to a suitable vessel, and the lend settled out. The clear solution is drawn off, and worked up into a pure stannate. Tho lead pre cipitate is washed—the washings being put into the decomposing pat—and heated nearly to redness upon an iron plate. It is thereby oxidized, and re-converted into titharge or red lead. Instead of the lead compound, hydrated sesquioxide of iron, or binoxide of manganese, manganate of soda, or other oxidizing substances may be used.
Stantinte of sodium is largely used in the dyeing and printing trades, going usually by the name of " proparing salts." Its and its applications depend upon its giving up stannic acid when an acid is mixed with it. The method of preparing the cloth is to pad it in n stannate solu tion and then puss it through n souring bath. The sulphuric acid forms sulphate of soda with the base of the salt, and the stannic acid remains attached to the cloth. The value of stantinte of soda depends upon the amount of tin which it contains. In the hydrated or crystalline salt, there should be 25 to 27 per cent. of water and no common salt. This latter substance is often added as nn adulterant.
Staunite of Sodium.—To prepare this salt 4 lb. of chloride of sodium, 13i lb. of caustic soda, and 4 lb. of feathered block tin, are fused in an iron pot. The mixture is kept well stirred and boiled to dryness. Stannite of sodium is used in dyeing and printing to some slight extent.