Barwood spirit is made with 5 gal. hydrochloric acid at 32° Tw., 1 gal. nitric acid at 64° Tw., and tin at the rate of 1 oz. per lb. of mixed acids.
Tin solution is used for very similar purposes to red cotton spirits, from which it is not distin guished by any well-marked outline. Such a solution is made with 6 gal. hydrochloric acid at 32° Tw., 1 gal. nitric acid at 64° Tw., 1 gal. water, and 7 lb. tin in rods. In working, the action should be brisk, and the surface of the liquid be covered with a small fine froth ; but there must be no orange vapours.
A purple cotton spirit is made by mixing 5 lb. hydrochloric acid and 1 lb. nitric acid, both of the usual strength, and dissolving 2 oz. tin per lb. of mixed acid. Afterwards, lb. bichromate of potash, dissolved in water, is added to every 18 gal.
Printers' Oxymuriates.—(1) Hydrochloric and nitric acid, 20 lb. each ; sal ammoniac, 5 lb., previously dissolved in 'Um nitric acid ; and dissolve in the mixture 10 lb. tin. (2) Melt 16 lb. tin crystals in a bowl set in hot water, and add by degrees 20 lb. nitric acid. (3) Melt in the same way 60 lb. tin crystals, adding I qt. water, and add gradually 92 lb. nitric acid at 60° Tw. (4) Hydro chloric acid at 34° Tw., 11 lb. ; nitric acid at 62° Tw., 5 lb. ; and dissolve gradually 2 lb. feathered tin. No. (2) is used for " cutting" madder pinks, and No. (4) for spirit styles.
Pink salt is a double chloride of tiu and ammonium. It is precipitated as a white powder, if a strong solution of the stannic) chloride (bichloride or perchloride of tin, free from nitric acid) is mixed with a saturated solution of sal ammoniac. Its uses have not been fully studied.
Stannate of soda, otherwise known as preparing-salt, is very extensively used in the steam-style of printing, and may also be used in fixing certain dyes, including aniline colours, upon cotton. It is generally made according to Young's process: good tin-ore, i. e. oxide of tin free from certain impurities, is heated to about 316° (600° F.), either with caustic soda or with a mixture of nitrate of soda and common salt, while a current of steam is passed over the mass. The whole, when cold, is dissolved in water, let settle, filtered, and boiled down.
To determine the proportion of tin in a sample, weigh out a known quantity, dissolve it in water, add a few drops of hydrochloric acid, and place in the solution some pieces of clean sheet zinc. By the action set up, the tin is thrown down as a metallic sponge. It is collected, washed in distilled water, dissolved in pure hydrochloric acid, and its quantity is ascertained by the method given above for tin crystals.
It is a great mistake to suppose that the comparative value of two samples of atannate of soda, or indeed of any other compound, can be ascertained by dissolving equal weights in equal measures of water, and taking the ap. gr. by Twaddle's or Beaume's hydrometer. Common salt, which is sometimes found in stannate to the extent of 28 per cent., raises the hydrometer, though it adds nothing to the value of the sample. Many compound stannates have been proposed in which arsenic, phosphorus, alumina, silica, and tungsten are used in place of a portion of the tin. Concerning these mixtures, the general opinion of the trade is not favourable.