in geometry, is the finding of a right line equal to a curve. The rectification of curves is a branch of the higher geometry, a branch in which the use of the inverse method of fluxions is especially useful.
TURKEY-RED, Levant-Red, and Adrianople-Red, the names indiscriminately given to that beautiful red dye which distinguishes the cotton manufactured in the Ottoman empire, and at Afracan in the dominions of Russia. We have two accounts of the process of communicating this dye to the stuffs; one by Professor Pallas as he saw it practised at Afracan; the other in the 92nd number of the Annales de Chimie by Citizen Felix. As every thing relating to useful manufactures is of general importance, we shall give pretty copious extracts from both papers.
According to Dr Pallas, the dye-stuffs employed at Afracan are, madder, fumach, gall-nuts, alum, an inferior kind of soda, and fish-oil. The process of dyeing is as follows:
The roots of the madder, when fresh gathered, are placed above each other in a stove, or in a pit dug in viscous earth which has been strongly heated. Earth is then thrown over the madder, and it must sweat until the stove or pit becomes cold; when the roots, the second or third days, are taken from it, and either spread out or hung up to dry. When it is thoroughly dried in the sun, the madder is ground to a very fine powder, as are likewise the round leaves of the fumach (Rhus cotinus). The fish oil is boiled from the entrails of the flurgeon and other large fishes; and the proof of its being proper for dyeing is, that when mixed with a lixivium of soda, it must immediately assume a milky appearance. Should that not be the case, it cannot be used by the dyers.
The cotton to be dyed red is first washed exceedingly clean in running water; and when the weather is clear, hung up on poles to dry. If it does not dry before the evening, it is taken into the house, on account Turkey: of the saline dews so remarkable in the country around Afracan, and again exposed to the air next morning. When it is thoroughly dry it is laid in a tub, and oil is poured over it till it is entirely covered. In this state it must stand all night; but in the morning it is hung up on poles, and left there the whole day; and this process is repeated for a week, so that the cotton lies seven nights in oil, and is exposed seven days to the atmosphere, that it may imbibe the oil, and free itself from all air. The yarn is then again carried to a stream, cleaned as much as possible, and hung up on poles to dry.
After this preparation a mordant is made of three materials, which must give the grounds of the red colour. The pulverized leaves of the sumach are first boiled in copper kettles; and when their colouring matter has been sufficiently extracted, some powdered galls are added, with which the liquor must be again boiled; and by these means it acquires a dark dirty colour. After it has been sufficiently boiled the fire is taken from under the kettle, and alum put into the still hot liquor, where it is soon dissolved. The proportion of these three ingredients cannot be ascertained, as the dyers vary that proportion at pleasure. The powder of the sumach leaves is measured into the kettle with ladles; the water is poured in according to a gauge, on which marks are made to show how high the water must stand in the kettle to soak six, eight, ten, &c., pounds of cotton yarn. The galls and alum are added in the quantity of five pounds to each pound of cotton. In a word, the whole mordant must be sufficiently yellow, strong, and of an alluring tint.
As soon as the alum is dissolved, no time must be lost in order that the mordant may not be suffered to cool. The yarn is then put into hollow blocks of wood shaped like a mortar, into each of which such a quantity of the mordant has been poured as may be sufficient to moisten the yarn without any of it being left. As soon as the workman throws the mordant into the mortar, he puts a quantity of the yarn into it, and presses it down with his hand till it becomes uniformly moistened, and the whole cotton yarn has stuck. By this it acquires only a pale yellow colour, which, however, is durable. It is then hung up on poles in the sun to dry; again washed in the stream, and afterwards dried once more.
The next part of the process is to prepare the madder dye. The madder, ground to a fine powder, is spread out in large troughs, and into each trough is poured a large cupful of sheep's blood, which is the kind that can be procured with the greatest facility by the dyers. The madder must be strongly mixed in it by means of the hand, and then stand some hours in order to be thoroughly soaked by it. The liquor then assumes a dark red appearance; and the madder in boiling yields more dye.
After this process water is made hot in large kettles, fixed in brickwork; and as soon as it is warm, the prepared red dye is put into it, in the proportion of a pound to every pound of cotton. The dye is then suffered to boil strongly; and when it is enough, which may be tried on cotton threads, the fire is removed from under the kettle, and the prepared cotton is deposited near it. The dyer places himself on the edge of the brickwork that incloses the kettle; dips the cotton yarn, piece by piece, into the dye; turns it round backwards and forwards; presses it a little with his hands; and lays each piece, one after the other, in pails standing ready for the purpose. As soon as all the cotton has received the first tint, it is hung up to dry; as the red, however, is still too dull, the yarn, which has been already dyed once, and become dry, is put once more into the dyeing-kettle, and must be left there to settle for three hours over a strong fire; by which it acquires that beautiful dark red colour which is so much esteemed in the Turkey yarn. The yarn is now taken from the dye with sticks; the superfluous dye which adheres to it is shaken off; the hanks are put in order, and hung up, one after another, to dry. When it is thoroughly dry, it is washed in the pure stream, and again dried.
In the last place, the above-mentioned soda is dissolved with boiling water in tubs destined for that purpose, and it is usual at Afracan to allow 20 pounds of soda to 40 pounds of cotton, or half the weight. Large earthen jars, which are made in Persia of very strong clay, a yard and a half in height, almost five spans wide in the belly, and ending in a neck a span and a half in diameter, inclosed by means of cement in brickwork over a fire-place, in such a manner that the necks only appear, are filled with the dyed cotton yarn. The ley of dissolved soda, which is blackish and very sharp, is then poured over it till the jars be filled; and some clean rags are pressed into their mouths, that the uppermost layers of yarn may not lie uncovered. A fire is then made in the fire place below, and continued for 24 hours; and in the mean time the steam which arises from the jars is seen collected among the rags in red drops. By this boiling the dye is still more heightened, and is made to strike completely; every thing superfluous is removed, and all the fat matter which still adheres to the yarn is washed out. Nothing more is then necessary for completing the dye of the yarn but to rinse it well several times in running water, and then to dry it.
Cotton cloth is dyed with madder at Afracan in the same manner; but many pursue a fraudulent process, by dyeing with red wood, and then sell their cloth as that which has been dyed in the proper manner.
The processes followed in the Grecian manufactories in the Levant, as described by M. Felix, varies in some particulars from this. The first process is that of cleaning the cotton; for which purpose three leys are employed; one of soda, another of ashes, and a third of lime. The cotton is thrown into a tub, and moistened with the liquor of the three leys in equal quantities; it is then boiled in pure water, and washed in running water.
The second bath given to the cotton is composed of soda and sheep's dung dissolved in water. To facilitate the solution, the soda and dung are pounded in a mortar. The proportions of these ingredients employed, are one oceca of dung, six of soda, and forty of water; each oceca being equal to about fifty ounces. When the ingredients are well mixed, the liquor expressed from them is strained; and being poured into a tub, six ounces of olive oil are added to it, and the whole is well stirred till it becomes of a whitish colour like milk. The cotton is then sprinkled with this water; and when the skins are thoroughly moistened, they are wrung. wrung, pressed, and exposed to dry. The same bath must be repeated three or four times, because it is this liquor which renders the cotton more or less fit for receiving the dye. Each bath is given with the same liquor, and ought to continue five or six hours. It is to be observed that the cotton, after each bath, must be dried without being washed, as it ought not to be rinsed till after the last bath. The cotton is then as white as if it had been bleached in the fields.
It may be supposed that the dung is of no utility for fixing the colours; but this supposition would be rash; for, as M. Felix observes, it is well known that this substance contains a great quantity of volatile alkali in a disengaged state, which has the property of giving a rosy hue to the red. It is therefore probable that it is by this ingredient that the red dyes of the Levant are indebted for their splendour and vivacity. This much, at any rate, is certain, that the Morocco leather of the Levant is prepared with dog's dung; because it has been found that this dung is proper for heightening the colour of the lack.
The process of galling, which follows the bath of dung, is performed by immersing the cotton in a bath of warm water, in which five ounces of pulverized gall-nuts have been boiled. This operation renders the cotton more fit for being saturated with the colour, and gives to the dye more body and strength. After the galling comes alumining, which is performed twice, with an interval of two days, and which consists in dipping the cotton into a bath of water in which five ounces of alum have been infused, mixed with five ounces of water alkalified by a ley of soda. The alumining must be performed with care, as it is this operation which makes the colouring particles combine best with the cotton, and which secures them in part from the destructive action of the air. When the second alumining is finished, the cotton is wrung; it is then pressed, and put to soak in running water, after being inclosed in a bag of thin cloth.
The workmen then proceed to the dyeing. To compose the colours, they put in a kettle five ounces of water, and five ounces of a root which the Greeks call alizarin, or painting colour, and which in Europe is known under the name of madder. The madder, after being pulverized, is moistened with one ounce of ox or sheep's blood. The blood strengthens the colour, and the dye is increased or lessened according to the shade of colour required. An equal heat is maintained below the kettle, but not too violent; and when the liquor ferments, and begins to grow warm, the skins are then gradually immersed before the liquor becomes too hot. They are then tied with packthread to small rods placed crosswise above the kettle for that purpose; and when the liquor boils well, and in an uniform manner, the rods from which the skins were suspended are removed, and the cotton is suffered to fall into the kettle, where it must remain till two-thirds of the water is evaporated. When one-third only of the liquor remains, the cotton is taken out and washed in pure water.
The dye is afterwards brought to perfection by means of a bath alkalified with soda. This manipulation is the most difficult and the most delicate of the whole, because it is that which gives the colour its tone. The cotton is thrown into this new bath, and made to boil over a steady fire till the colour attains the required tint. The whole art consists in catching the proper degree; a careful workman, therefore, must watch with the utmost attention for the moment when it is necessary to take out the cotton; and he will rather burn his hand than miss that opportunity.
It appears that this bath, which the Greeks think of so much importance, might be supplied by a ley of soap; and it is probable that saponaceous water would give the colour more brightness and purity.
M. Felix seems doubtful whether the alizarin of the Greeks be the same plant with the European madder. If it be, its superiority must arise from the mode in which it is cultivated, and the method employed to dry it. The alizarin is not collected till the fifth or sixth year of its growth, when it has acquired its full strength; and as it is the woody part of the roots which affords the greatest quantity of colouring particles, this must give it an obvious superiority over madder, which is collected before it has arrived at maturity. The mode of defecation contributes also, in the opinion of our author, to improve the quality of the alizarin. The Levantines dry it in the open air; and this operation is easy in a country where great dryness prevails in the atmosphere; while in our damp climates we are obliged to dry the madder by flames. Hence it happens that the smoke, which mixes itself with the cold air, and penetrates the roots, impregnates them with fuliginous particles, which alter the colouring substance; an accident which does not take place when the madder is dried without the assistance of fire.
For the philosophical principles of these processes of dyeing, see Animal and Vegetable Substances in this Supplement.