Some compounds of tin are used in dyeing which probably contain an oxide intermediate between stannous and stannic. These solutions are of a rich deep-amber colour, and in warm weather keep very badly. Of these mordants, the most important is nitrate of tin, scarlet spirit (or bowl spirit), much used in Yorkshire and in Scotland for grounding cochineal colours on woollens and worsteds.
To prepare this spirit, a quantity of so-called "single," or "dyers' " aquafortis, i. e. nitric acid at about 32° Tw., containing a quantity of hydrochloric acid, or of an alkaline chloride, and totally free from sulphuric acid, and from the lower oxides of nitrogen, is placed in a large clean stoneware bowl. The finest quality of grain-bar tin, not feathered, is then dissolved in it, in the proportion of 1 lb. to every 8 lb. of the acid. Certain niceties in working are essential to success. If the acid is average in quality, and the weather is temperate, some 4-5 rods are laid in the bowl, and allowed to dissolve quietly, without stirring, or the application of heat. After a time, the liquid "turns," L a. assumes a deep-amber or light-orauge colour. When this has occurred, all difficulty is over, and nothing is needed but to add the rest of the tin by degrees, taking care that the reaction neither dies down nor grows violent. There must be no effervescence, nor production of orange-coloured bubbles or fumes. If the process fails, the change of colour does not occur, and the liquid, after remaining colourless for some hours, suddenly turns thick and turbid. If too much tin has been introduced at first, orange fumes rise up, and the tin is deposited in an insoluble state, and is useless. In winter, 8-10 rods may be put in at the beginning, without danger. In hot weather, two or even one is sufficient, and, if convenient, the howl may be cooled by placing it in a stream of cold water. If the temperature is very high, the spirit may be started by putting into the bowl half a handful of dry, clean, granulated tin. Nitrate of tin, if well made, marks 58°-60° Tw., and contains 2; oz. tin per lb.
Purple Spirit, for producing wood purples and violets upon wools and worsteds, is made as follows : —Fresh, well-made nitrate of tin is gently warmed by setting the bowl in a larger vessel of hot water, and is allowed to dissolve as much grain-bar tin, in the rod, as it can take up. It marks about 80° Tw., and should be used immediately.
Aniline Spirit, so-called, is used for fixing aniline colours upon the cotton warps of delaines, &c., and for producing some very rich shades with dye-woods. It is prepared from 5 lb. single aqua
fortis at 32° Tw., 21 gal. hydrochloric acid at the same strength, and 12 lb. grain-bar tin in the rod. The acids are mixed in a bowl with upright sides. About 12 rods are put in at first, arranged at equal distances round the side of the bowl. More tin is added as these dissolve, but the tempera ture must not become excessive. The finished spirit is of m reddish-amber colour, and contains about 20 oz. of tin per lb.
Many recipes, in which tin is directed to be dissolved in different proportions of nitric acid, with the addition of sal ammoniac, will yield a mordant similar in properties to the above.
The stannic salts or per-salts of tin are prepared by two very different processes : (1) A pure aqueous stannic chloride, otherwise called perchloride of tin, bichloride of tin, stannic hydrochlorate, dyers' composition, and sometimes scarlet spirits, may be obtained by saturating double muriate of tin at the highest strength, with chlorine gas till a small portion, taken out and dissolved in water, no longer gives a black precipitate with a solution of mercuric chloride (corrosive sublimate). The solution, with or without the addition of tartaric or oxalic acids, may be used for dyeing cochineal and Inc wallets upon wool. Or (2) tin crystals are dissolved in hydrochloric acid, heat is applied, and nitric acid is added in small proportions at a time, avoiding excess, till the above-mentioned black precipitate is no longer obtained. Or the metal is dissolved in mixtures of nitrie and hydro chloric acids. Whenever nitric acid is used, it is never entirely driven off, and the resulting product differs in its action upon colours from that obtained by other processes. Hence it is improbable that pure tin composition would give all the results obtained with these mixtures. The following prescriptions may serve as specimens : Red cotton spirit, known also as crimson spirit, is made by mixing 6 gal. hydrochloric acid at 32°-34° Tw., 1 gal. nitric acid at 64° Tw., and I gal. water. After standing for a short time, enter by degrees 6 lb. of tin in the rod, beginning with 6 rods more or less, according to the weather, and adding the rest by degrees. The mixture must never get very hot, so as to give off orange vapours, nor must it ever be stirred. In 8-9 hours the whole of the tin will be dissolved, and the liquid will be of a clear pale straw-colour. Another red cotton spirit is made with 8i gal. hydrochloric acid at 35° Tw., 11 gal. nitric acid at 64° Tw., 1 oz. bichromate of potash, and sufficient tin to bring up the ap. gr. of the solution to 54° Tw.