MADDER.

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five times its weight of sulphuric acid of sp. gr. 1714, or 143 0 Tw. By thisoperation a portion of the ligneous and peCtic matters become so disintegratedas to be soluble in water. The magma of fieur de garance and acid is there-fore poured into a very large bulk of water, when a sediment is thrown down,which, after having been thoroughly washed, dried, and pulverised, becomesa fine brick-red powder, known in commerce as “carmine-madder.” Thismaterial has a tinctorial value exceeding that of madder by seven or eighttimes. Owing to practical difficulties, and the expense of production on thelarge scale, this substance has never been manufactured to any extent. Ityielded, when tried on the small scale, exceedingly good results in dyeing.

Second Group .—

Mechanical Process of Purifying Madder.—M. Pernod has tried towash the previously coarsely ground madder root upon a metallic wire gauzesieve under a current of water, whereby the colouring matter is carriedoff, while there remains on the sieve a greyish-looking, woody, fibrous materialnot containing any more colouring substances. The pigment washed out isallowed time to settle under water. The water is run off, and the substanceis placed on filters and dried. The brown powder thus obtained has atinctorial value seven or eight times greater than that of flowers of madder,yet it contains, as might be expected, a large quantity of foreign matter.

The processes based upon the solution and consequent extraction of thecolouring matter of madder are very many; indeed we may say that nearlyall the solvents capable of taking up the colouring matters from madder havebeen tried to produce what may be in a general way called extracts of madder.Many of these materials have a high tinctorial value, exceeding from twentyto seventy times that of the same weight of madder. These substances aresometimes named after the vehicle employed for extraction. Thus we havethe alcoholic, methylic, glyceric, and acetic extracts, to which names areusually added those of the inventors. These substances contain in generalthe colouring matters more or less contaminated with resinous and extractivematter. When these madder derivatives are treated repeatedly with a boilingsolution of alum the resinous matter is left, while the colouring principles aredissolved. The same result is obtained when these extracts are exhaustedwith water heated under pressure to 250°. As far as these substance havebeen actually employed, they have answered well in dyeing printed fabrics,especially if chalk is added. The bath requires almost a boiling heat, and,in order to exhaust the colouring matter, it is best to rub the dry extractup with alcohol, and to use far less water in the beck than with raw madder.When madder and flowers of madder are aCted upon by any neutral solvent,e.g., alcohol, wood-spirit, sulphide of carbon, glycerin, or by mild alkalinesolvents, as carbonate of soda, phosphate, pyrophosphate of soda, weakcaustic soda, or any alkaline borate, silicate, or oleate, that portion only ofcolouring matter is extracted which exists in a free state, while the portionintimately combined with the ligneous matter is left untouched. A completeexhaustion of the colouring matter can only be effected by the aid of mineralacids, which disintegrate the woody fibre and decompose the calcareous com-bination of the colouring matters. Hence it is clear that the preparation ofthe above extracts can be only suitably performed with either fleur de garanceor garancin, or with charbon sulfurique.