tartar is added. The cloth is then put in and kept till it is saturated. A double decomposition takes place; the nitro-muriatic acid combines with the potash of the tartar, while the tartareous acid dis solves the oxide of tin. When tartar is used, therefore, in any considerable quantity, the mordant is not a nitro-muriate, but a tartrate of tin.

The murio-sulphate of tin, produced by dissolving tin in muriatic acid, combined with about onefourth of its weight of oil of vitriol, is also a valuable mordant, and is preferable to the last for some purposes; it is also less expensive.

The oxide of iron is also a very useful mordant, and all kinds of cloth have a strong affinity for it. The permanency of the iron spots on linen and cotton is a sufficient proof of this. Iron, as a mor dant, is used in different states. Wool is dyed generally by means of the sulphate of iron, which may also be used for cotton. Acetate of iron, prepared by dissolving iron in vinegar, sour beer, &c., is preferable for some purposes. The pyro-ligneous acid, which differs from the acetic only in having in combination a certain quantity of empyreumatic oil, is at present preferred to the sulphuric, or acetic.

The astringent principle, or tannin, is also employed as a mordant, and has a strong affinity for cloth, and also for colouring matters. An infusion of nut-galls, sumach, oak bark, or any other substance containing tannin, is made in water, and the cloth is kept in it till it has absorbed a sufficient quantity of tannin. Silk has so strong an affinity for tannin, that manufacturers sometimes employ this circumstance to increase the weight of their silk.

A compound mordant is sometimes produced by impregnating the cloth first with oil, then with the

astringent principle, and, lastly, with the aluminous mordant. This is employed in dyeing the Adrianople red.

Several other substances are used as mordants occasionally, either as principals, or to facilitate the combinations of others with the cloths; such as nitrate of bismuth, oxide of arsenic, corrosive sublimate, acetate of lead, sulphate, or acetate of copper, &c.

The chief use of mordants is to render the dyes permanent, but they have also considerable influence on the colour produced: thus, the same colouring matter will produce very different dyes, according to the mordant used to fix it. If the aluminous mordant be used for cochineal, the colour will be crimson; but if the oxide of iron be used for the same colouring matter, black will be the result.

It is necessary, therefore, to choose such mordants and colouring matters as together shall produce the desired colour. And this principle enables us also to produce various colours with the same dye-stuff, only by changing the mordant.

It is probable that the whole of the surface of the fibres of cloth are not covered by the colouring matters precipitated upon them; but that the particles of colour are at some distance from each other. For cloth may be dyed different shades of the same colour; that is, it may be dyed deeper a second time than at first, by increasing the quantity of colouring matter, which could not be the case if the whole surface were covered. Another circumstance renders this opinion probable; all those colours which dyers call compound are made by dyeing the cloth first one colour, and then another thus, green is got by dyeing cloth first blue and then yellow.

In dyeing, the water employed should be as pure as possible, and the exact temperature in each process should be attended to. The dye-houses should be spacious, light, and airy, and cleanness is essentially necessary. The stuffs are supported in the cauldrons, or baths, by proper apparatus, and are drawn through them by a winch, or reel,

Of Dyeing Red.

The colouring matters employed for dyeing red are cochineal, kermes, madder, lac, Brazil-wood, logwood, and carthamus. Cochineal is a species of insect (the coccus cacti, Lin.) brought from America. The decoction of it affords a very bright crimson colour, inclining to violet. When alum is added to this decoction, it combines with its colouring matter, and forms a red precipitate. Muriate of tin gives a still more beautiful colour.

Kermes is also an insect found in several parts of Asia, and the south of Europe, which furnishes a red dye, by some thought not inferior to cochineal, but which has not been so much used since the introduction of the latter.

Madder is the root of a plant (rubia tinctorium, Lin.) The colouring matter of madder is extracted by water, either cold or hot, and precipitates of various shades of red may be obtained by alum, chalk, acetate of lead, and muriate of tin.

Lac is a colouring matter of animal origin, produced in the East Indies, from the coccus lacca, a small winged insect. This insect forms cells for its young, as regular as the honey-comb, but differently arranged; and the lac is procured from the substance of which these cells are made. The whole matter of these cells is called stick lac; when the

red colouring matter is extracted by water, what remains is a resinous substance called shell lac, used for various purposes, as varnishes, sealing wax, &c. Water dissolves lac, and the decoction is of a deep crimson colour. The precipitate, with alum or nitro-muriate of tin, forms a fine red.

Brazil-wood is an article used in dyeing. It is the central part of a large tree, that grows in Brazil. It is heavier than water, and affords a decoction of a red colour with water. The precipitate, with alum and nitro-muriate of tin, is a fine red.

Peach-wood gives a colour inferior to Brazil, and also in smaller quantity.

Logwood affords à colouring matter extensively used in dyeing. It is very heavy, and sinks in water. Its decoction is yellow, but by alum becomes violet or purple; by sulphate of iron it becomes black.

Carthamus is the flower of a plant cultivated in Spain and the Levant. It contains two colouring matters; a yellow, which is soluble in water; and a red, which is insoluble in water, but soluble in alcaline carbonats. The red colouring matter of carthamus, extracted by carbonate of soda, precipitated by lemon-juice, and ground with talc, constitutes the rouge employed as a cosmetic: the fineness of the talc, and the proportion of it mixed with the carthamus, occasion the difference between the cheaper and dearer kinds of rouge.

Wool is died scarlet, which is the most splendid of all reds, by cochineal. Alum will do as a mordant for fixing the red; but nitro-muriate of tin, or what is still better, the murio-sulphate of tin, are now used as preferable mordants. To die wool scarlet, à bath is made by mixing pure tartar with a little cochineal and nitro-muriate of tin; but as

the red produced by cochineal alone is rather a crimson than a scarlet; and as the colour of scarlet is, in fact, crimson and yellow, some yellow dye, or fustic, turmeric, or quercitron bark, is added to the cochineal in the first bath.

Into this the cloth is put, and boiled for two hours. It is then washed, and afterwards put into a second bath of cochineal, which is called the reddening. When crimson is the colour to be given to the cloth, the tin mordant is the best; but sometimes the dyers use the alum for this purpose, and then a decoction of cochineal. The addition of archil and potash renders the crimson darker, and gives it more bloom, but this is very fugitive. For paler crimsons, some madder is substituted for a portion of the cochineal. Wool is dyed madder-red, by boiling it first two or three hours with alum and tartar, and then in a bath of madder.

Silk may be dyed crimson with cochineal or Brazil-wood, and sometimes carthamus is used. The nitro-muriate of tin is the best mordant, but alum may be also used. Madder does not give a colour sufficiently bright.

Poppy colour, cherry, rose, and flesh colour, are given to silk by carthamus or Brazil-wood. When the carthamus is employed, an alcaline solution is made, and as much lemon-juice as will give it a fine cherry-red is poured into it.

It is extremely difficult to give silk a scarlet, and it is scarcely possible to give it a full scarlet. The murio-sulphate of tin, as a mordant, is first used, then the bath of cochineal and quercitron, and lastly, the cochineal bath alone. A colour approaching to scarlet may also be given to silk, by dyeing it first crimson, then dyeing it with carthamus, and lastly yellow, without heat.