Lac (Fa., Lague des lades; GER, Lackfarbe).—This long-known dye-stuff is extracted from gum-lao (see Resinous Substances) by the following process :—The crude lac is coarsely ground, and immersed for 16 hours in a cistern of water ; it is then trodden by men for about 4 hours, or until the colouring matter seems to be thoroughly extracted. The whole is then strained through cloths, while boiling alum-water is added ; the coloured water is run through two or three settling tanks, remaining for about a day in each, by which the colouring matter is deposited. This is taken up, and placed on a canvas strainer till free from water (2-3 days); it is then pressed, to extract the remaining moisture, and, at the same time, formed into square cakes bearing the maker's name. Such is the general mode of preparation. An improved plan, adopted by Elliott Angelo, at Cossipore, is as follows :—Tho crude leo is placed in a horizontal disintegrator, supplied internally with water ; the material is then broken very small, and the dye is extracted ; should the water contain no lime, a little is added, to facilitate the precipitation of the colouring matter. The whole is left to soak for 24 hours in a large vat ; the liquid is then drawn off through a series of settling tanks, each at a lower level ; the clear water is drawn off at the top, and the sediment is collected, passed through strainers, left to consolidate, and pressed into cakes, which are dried in the sun. The exports of the dye-stuff from Bengal, in 1875-6, were : —to the United Kingdom, 9655 cwt.; America, 680 cwt. ; France, 256 cwt. ; other countries, 5 cwt. British Burmah, in the same year, exported 72 cwt. to England. The competition of coal-tar dyes has thoroughly crippled a once flourishing industry ; the value of this dye-stuff in the Calcutta market has gradually fallen from 85 rupees a mauncl(of 82 lh.) in 1869, to 15 rupees in 1876, for finest quality ; while inferior qualities, formerly worth 25-53 rupees, are now unsaleable. The London market prices are approximately as follows :—D T, 10d. a lb. ; B Mirzapore, 9-10d. ; J E & G Mirzapore, ; other good and fine, 5-10d.; ordinary and native, 1 i-5d.
Lan.—This is a Chinese product, very common in the provinces of Kouang-Toung, Fokien, and Tche-Kiang It is derived from the fresh leaves of an acanthaceous plant, and yields a light blue on cottons.
Laureline.—This name has been given to some new colouring matters, which Dr. W. H. Gregg, of New York, is engaged in extracting from camphor. The main production hitherto has been yellow, in a variety of shades, and peculiarly brilliant and fast. It promises also to be cheap, and easily manipulated.
Litmus (Fa., Tourneso/ ; GER„ Lackmus).—The colouring principle of orchella (q. v.) receives this name, when it is prepared in the following manner :—Lime and carbonate of potash are added to the ground lichen and urine ; in 3-4 weeks, a blue colour is developed ; this is mixed with gypsum or chalk, and dried. It is used in Holland for colouring cheese ; by dyers, to produce crimsons ; and in the staining of chemical test-papers.
Logwood (Fa., Bois d'Inde, Bois sanglant ; GER, Blauliolz).—This well-known dye-stuff is the heart-wood of Hcematoxylon Campechianum, a tree of moderate height, growing abundantly in Hon duras and Mexico (as a native), and in most of the W. Indies (naturalized). The trees may be felled when about 10 years old ; the bark, and the alburnum or white sap-wood, is chopped off, and the red heart-wood is cut into logs of about 3 ft. in length. The wood is dense and tough, but splits easily ; it is very little affected by exposure, remaining brownish-red internally but acquiring a blackish-red tint externally. The felling, barking, and shipping of the wood constitute an important industry in the districts where it grows. Our imports in 1878 were contributed as follows :—British W. Indies,
19,621 tons ; British Honduras, 11,147 ; Hayti and St. Domingo, 4541 ; Mexico, 1826 ; other countries, 1176. In 1879, they were respectively :-23,641, 10,680, 4964, 3205, and 2063 tons. Four kinds are distinguished in the London market :—" Campeachy," 71. 15s.-81. 10s. a ton ; " Honduras," 71. 10s.-71. 15s. ; " St. Domingo," 61. 10s.-61. 15s. ; " Jamaica," 61.-61. 15s. Hamburg imports about 20,000 tons yearly. Logwood chips are used medicinally, for the astringent principle (see Drugs). For dyeing purposes, the logs are reduced to a coarse powder, by means of machinery ; the powder is moistened, and laid in beds, 15-20 ft. long, 10-12 ft. wide, and about 3 ft. thick ; fermentation ensues, by which the colouring principle, Hiematein, is liberated. Large quantities of extract also are prepared. For this purpose, the wood must not be too highly oxidized; the solution obtained from it by repeated lixiviation is slowly concentrated at a temperature not exceeding 654° (150° F.). This extract is much employed in calico-printing. Both the wood and the extract are extensively employed to produce cheap blacks on mixed fabrics. The exports flout St. Domingo, in 1878, were about 1122 tons, half of which went to the United States, partly for re-shipment to Europe. Havre consumes large quantities. The exports from British Honduras, in 1878, were 13,704 tons. Under existing circumstances, this colony could easily keep up au export of 8000-10,000 tons annually ; and a few seeds scattered, or a few trees planted, in any swampy ground, suffice to ensure a regular crop of the dyewood every 8-10 years.
Madder (Fs., Garance ; GEE., Krapp).—Tbe useful dye-plant, Bubia tinctoria, is very widely distributed, from S. Europe to E. Asia. In Central and S. Europe, it is still extensively cultivated though the development of the artificial manufacture of alizarine (see p. 683) is gradually driving the plant from Western markets. It is hardy, and withstands frost and drought ; during the first winter, care must be taken, in very cold situations, that the heaving of the ground shall not expose the roots. It is propagated by sets or shoots ; the best soil is a deep rich loam, containing abundance of lime salts. Planting is effected in small furrows, 3 in. deep, and 8-10 ft. apart, with a space of about 1 ft. between the roots. The ground is hoed to keep down weeds ; and when the plants are 12-15 in. high, their tops are bent down to the ground, and covered. with earth, except at the ends. In France and Holland, this last operation takes place in November ; the practice is of questionable value, unless when sets are required for next year's planting, as it encourages " runners," which are valueless for dyeing purposes. A better plan is to out off the herbage, which forms excellent fodder. The roots may be gathered in the 3rd year ; in Turkey and the East, they are often left till the 5th-7th year, that the colouring matter may be more thoroughly developed by the oxidizing influence of the air. The benefit of this plan is, however, often connteracted by the attacks of fungi. The roots are removed singly from the ground, in August-September, and are thoroughly washed, dried, and stacked away. The drying is variously performed by sun-heat, in the shade, and by stove-heat, Fresh roots yield about 24 per cent. of commercial madder. The dried roots are selected according to quality, and ground to a fine powder, a process which is ren dered very easy by the extreme brittleness of the root. The powder is stored in casks, and is said to improve by keeping for 2-3 years, but to deteriorate greatly beyond that time. The colouring matter resides almost entirely in the cortical part of the root. The best samples are grown on cal careous soils.