LOGWOOD.

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space than the modern chrome-blacks. These are rapidly completed, and lookwell for a time, but on prolonged exposure to dire# sunlight they assume anunpleasant greenish hue. A logwood and copperas black upon a vatted—or,as it is technically termed, woaded—bottom yields in permanence only to amadder-black upon the same ground. It is not inappropriate to remark thatdyers have much less inducement to study fastness than was formerly thecase, as the rapid changes of fashion leave consumers no time to discover thefugitive character of the shades.

By adding, to the logwood or its deco#ion, fustic,* santal wood, turmeric,and alum, there are produced upon woollen fabrics, previously mordantedwith bichromate and cream of tartar, beautiful bronze colours, of variousshades. The dyeing operation is carried on at boiling heat.

Steam-blacks for wool are made up of—Extra# of logwood; a salt ofcopper (sulphate, chromate) as oxidising material; alum as mordant; per-nitrate of iron as mordant, and oxalic acid ; sometimes bichromate of potassaand sal-ammoniac are also added.

Steam-grey for wool contains—Extra# of logwood ; nitro-sulphate of iron.Logwood is also employed for some kinds of steam-brown and fancy colours onwool.

Steam-black upon silk is produced by printing a properly thickened mixtureof logwood deco#ion, extra# of nut-galls, a salt of copper, generally thenitrate, and a proto-persalt of iron.' Silk is dyed black by means of logwood,or the decodtion thereof, after having been mordanted in either sulphate ofiron (proto-salt), or in a mixture of that salt and nitro-sulphate of iron, or alsoin nitrate of protoxide of iron. Silk is very frequently dyed black by a twiceor thrice times repeated immersion in the dye-beck, and the colour is modified,if required, by the addition of fustic. If the proto-nitrate of iron is used as amordant for silk, that material, after dyeing, becomes very harsh, and its sup-pleness and pliancy is therefore restored by padding in emulsified olive oil.The brilliancy of black silk is often enhanced, and its weight very considerablyincreased, by immersion in a solution of subacetate of lead, and exposure toan atmosphere of sulphuretted hydrogen gas.

Logwood dyes are detected on dyed fabrics by the following tests:—Logwood-black dyed tissues leave, on incineration, ash composed of peroxideof iron, or a mixture of that oxide and alumina, or also, sometimes, of oxideof chromium. The dyed tissues are discharged by chlorine and hypochlorites,and are turned red by hydrochloric acid and tin-salt: when the reddenedspot, while yet moist, is pressed against white filtering-paper, it yields thereona cherry-red stain, which turns blue if touched with a glass rod moistenedwith aluminate of soda.

The lilacs or violets produced by logwood leave, on incineration, a whiteash containing alumina: the dyed tissues are discharged by chlorine andhypochlorites, and turn red with hydrochloric acid, presenting, further, thesame features as those just described for black. When the lilac or violetgoods are put into milk of lime, and next washed with soap, the colour isdischarged.

* Of this we shall say more hereafter, but it may be briefly stated to be the wood of theMonts tinctoria. It is known in the trade also as Cuba wood, and largely used, especially inwoollen dyeing.