SODA, called sometimes mineral alkali, is another of the fixed alkalies; it forms the basis of common salt, that being a muriate of soda; soda, under the name of _barilla_, is used in making soaps, and also in dyeing. SULPHUR, or BRIMSTONE, is scarcely used for dyeing in its crude state, but when combined with oxygen forming _sulphuric acid_, as well as when that acid is combined with various bases, as _iron_, _alumina_, &c. it becomes of great importance in this art; see SULPHURIC ACID. SULPHATE OF IRON, see IRON above. SULPHURIC ACID was for many years, and still is called by the vulgar, _oil of vitriol_, because it was formerly obtained from green vitriol or sulphate of iron, but the more simple and ingenious processes of modern chemistry have superseded the old methods; sulphuric acid is now obtained by burning sulphur with a certain portion of saltpetre in large leaden cisterns. The acid fumes sink into the water placed at the bottom of the cistern, the water being afterwards boiled away: the acid is afterwards purified by retorts, placed in a sand heat. The specific gravity of good sulphuric acid should be 1.85. SUMACH is the production of the _rhus coriaria_, a shrub which grows naturally in Syria, Palestine, Spain, and Portugal. It is cultivated in the two last countries with great care. Its shoots are cut down every year quite to the root, and after being dried are reduced to powder, and thus prepared for the purposes of dyeing, &c. Sumach bears a great resemblance, as an astringent, to galls. Sumach alone gives a brown and a fawn colour, but cotton stuffs impregnated with acetate of alumina take a durable yellow from it. TARTAR, see ARGOL. TIN, dissolved in nitric or muriatic acid, forms solutions of great importance in many processes of dyeing, particularly scarlet. These solutions are called respectively _nitrate_ and _muriate of tin_. TURMERIC is a root obtained from a plant growing both in the East and West Indies. The root is used chiefly for dyeing yellow; but it is a fugacious colour. VERDIGRIS is a crude _acetate of copper_, obtained by exposing copper plates to the husks, &c. of grapes, which containing considerable acetic acid, the acid combines with the surface of the copper plates, forming a blueish green rust, which is scraped off, and forms the verdigris of commerce. A still more complete acetate of copper is obtained in _distilled verdigris_, which is in elegant green crystals. The best verdigris is made in France; some is now also made in this country. WELD, sometimes called improperly WOULDS, _dyer's-weed_, or _Reseda luteola_, is a plant found wild, in this country, but cultivated for the purposes of the dyer; it is much used for yellows.