LAC DYE.

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violet, its taste being astringent and bitter. It is insoluble in water, to whichit, however, imparts its colouring matter, rendering it red. It is partly solublein alcohol, yielding a red solution, but it is insoluble in fatty and essentialoils. Its composition is, according to Hatchett—Resin, 68; colouringmatter, 10; wax, 6 ; gluten, 5’5 ; foreign matters, io’5. Dilute sulphuric andhydrochloric acids are better solvents for the colouring matter than water,whence they are applied in the lac-dyeing process. The best kind of thisvariety of stick-lac is imported from Siam, the Bengal product being veryinferior.

2. Grained lac consists of the cells detached from the wood of the branches.It-occurs in small, variously-shaped, broken-up pieces, and, as met with in trade,is frequently robbed of a portion of its colouring matter by treatment withwater. It consists of—Resin, 88*5 ; colour, 2‘$ ; wax, 4*5 ; gluten, 2*0 ; woodyfibre, sand, &c., 2.

3. Lac in the shape of cakes is simply the material just mentioned afterhaving been fused and cast into moulds.

4. Lac in the shape of thin scales is obtained in the following manner:—The crusty resinous substance is pulled from the branches of the trees, brokeninto small fragments, macerated for twenty-four hours in cold water, washed,dried, and put into a bag made of stout calico, which is tied at the mouth,and placed over a clear charcoal fire. The resin liquefies, and on pressurebeing applied the molten material runs in thin layers over a plank of polishedfig-tree wood, when it soon solidifies. This material goes by the nameof shellac, and contains 91 per cent of resin, only about £ percent of colouringmatter, while the rest is wax, gum, and other substances.

Lac-lake and lac-dye are the secondary- or by-produdts of the process justdescribed, carried on with the following modification :—The crude matter astaken from the trees is coarsely powdered and exhausted by maceration in hotwater, to which sometimes a little soda is added. The liquid thus obtained,sometimes after previous filtration through coarse canvas, is evaporated inpans placed on a charcoal fire, or left to spontaneous evaporation by the sun’srays in shallow earthenware vessels. The dry residue is in the shape ofsquare cakes, 36 millimetres by 13. This material consists on an average of—Resin, 25 ; colouring matter, 50; earthy impurities, 22. It is shipped fromCalcutta, and is chiefly brought to London and Hamburg. This substancebas been known and prepared in India for centuries ; its English name wasgiven to it by Mr. Stephens, who at the end of the last century made it knownin Europe.

Although the colouring matter of lac-dye is analogous to that of cochineal,its identity is not established, the shades produced being less bright but morepermanent. The richness of this and similar products in colouring matter isdetermined in the same manner as has been stated for cochineal, viz., by adyeing process on the small scale. The lac-lake is obtained by precipitatingwith alum the decodtion of stick-lac prepared with weak caustic soda. Theensuing deposit is pressed, moulded into cakes, and dried. It consists of—Colouring matter, 50; resin, 40; alumina, 9; impurities, 1. For dyeing it isbest first decomposed by weak hydrochloric or sulphuric acids. There are metwith in commerce a great number of brands of lac-lake and lac-dye, but thehade-mark is no guarantee of the quality.

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