By omitting the quercitron-bark, the above process will afford a rose-colour. Scarlet may be changed to crimson by boiling the cloth in a solution of alum till the shade desired is obtained. Alkalies and earthy salts in general havethe same effect as alum.
Yellow is a colour but rarely required in the dyeing of wool, yet, as it fre quently forms the base of other colours, it may be proper to notice it. Weld funk, and quercitron bark, furnish the best yellows : weld is a plant which is both cultivated and grows wild in this country ; the stem is slender, and rises to the height of three or four feet; the entire plant is used in dyeing, and is gathered when it is ripe : the shortest and slenderest stems are the most esteemed. Fustic is the wood of a large West Indian tree. Quercitron grows in great abundance in North America, and is there called yellow oak; its bark is the only part used for dyeing.
The colours obtained from weld and quercitron both nearly resemble each other in shade, and also in durability, which is not great ; but the bark contain ing the largest quantity of colouring matter is not only the most convenient to. use, but upon the whole the cheapest. Dr. Bancroft has given the best direc tions for its use. He directs a deep and lively yellow to be thus prepared for wool :—Let the cloth be boiled for an hour or more, with about one-sixth of its weight of alum dissolved in a sufficient quantity of water; then plunge it with out rinsing into a bath of warm water, containing in it as much queratron bark as equals the weight of the alum employed as a mordant. The cloth is to be
turned through the boiling liquid until it has acquired the intended colour. Then a quantity of clean powdered chalk, equal to the hundredth part of the weight of the cloth, is to be stirred in, and the operation is completed. The object which the dyer has in view is to give his ,tuffs a uniform and durable colour, at the same time that he entirely preserves their original texture. He therefore uses colours in solution, in order that their particles may apply them selves to the individual fibres of the stuff, according to their affinity for it. When. for example, a quantity of wool, freed from all impurity, is dipped into the solution of any colouring matter, if the fibres of the wool have a stronger attraction for the colouring matter than the water or other menstruum which holds that colour in solution, the colouring matter will leave its solvent, and apply itself to the wool, which will by that means be dyed ; its fibres will have become covered with colouring matter; and if their attraction for it be so strong that the action of soap, air, and light, or other ordinary means of exposure, shall have no per ceptible effect in decomposing the combination, orin other words, of injuring its tinge, the colour is said to be permanent; so that dyeing is in fact a chemical process, and the application of animal and vegetable bodies depends on their chemical affinities.