acid salts and at a high temperature, by means of which a sort of solution is obtained while in contact with the fibre itself. The art of the dyer consists in so arranging these three elements-fibre, metallic salts, and colouring matterthat he may obtain the formation of the insolubie coloured lake in the body of the fibre itself, whereby either by the lake being mechanically retained or chemically combined the fibre is permanently coloured..

There are other cases of dyeing closely resembling the foregoing, in which the resulting dyed stuff may be considered as being a binary compound of fibre and colouring matter, but in which the methods of application are less simple. These may be taken generally as consisting in the use of materials or processes which bring a previously insoluble colouring matter into a soluble state; thus the pink colours of safflower are obtained by the action of an alkali; and the dyes yielded by archil, arnotto, and indigo are also the result of the action of solvents. It is possible that during the process of solution important internal changes may take place in the composition of the above dyes, but if so, they are only of a temporary nature, for there is no reason to suppose that the colouring matter attached to the fibre differs in chemical composition from that which is free.

> With regard to nearly all other colouring matters, the above simple processes are quite powerless to induce a permanent combination with the fibre. Let wool or silk be immersed at boiling temperature in decoctions of any of the best known natural dye-stuffs, such as cochineal, logwood, madder, quercitron bark, &c., and then washed in water, it will be found that the fibres are simply discoloured, or stained of no definite shade; they have taken up but a small portion of colour from the decoction, and no real dyeing has taken place.

Use of Mordants.-To obtain permanent dyes from the great majority of native colouring materials the intervention of another class of bodies entirely different from either fibrous or colouring matter is found necessary; these bodies are called mordants. The term mordant is found in Latin and Italian manuscripts of the 12th and 13th century, as the name of an adhesive composition by means of which gold leaf could be attached to wood, marble, or metal; early dyers appropriated the word to designate a substance by means of which colouring matters could be made to adhere to fibre, and it has been retained in that sense in all modern treatises upon dyeing.

The chief mordants used in dyeing are salts of aluminium, iron, tin, chromium, copper, and a few other metals. When a decoction of a colouring matter, say logwood or cochineal, is heated with a small quantity of a properly chosen salt of one of these metals, it is found that the colouring principle loses its solubility, forms a combination with the metallic salt or its bases, and precipitates to the bottom of the solution, leaving the supernatant liquid nearly or quite colourless. The precipitate is usually called the "lake" of the particular metal and colouring matter, which are probably in a state of chemical combination; the lakes are insoluble in water, and are only split up again into their constituents by the action of somewhat powerful chemical agents.

Fibre cannot usually be dyed by means of ready formed lakes, for the reason that they are insoluble in water and not easily soluble in any-menstruum which can be safely applied to such material; they are themselves of too coarse and gross a nature to penetrate the fibre, and when applied to it rest for the most part on the surface, and are therefore easily removable by washing or mechanical friction. It is known, however, that for some colours in calico-printing

Application of Mordants.-There are three principal ways in which the mordant and colouring matter can be put into contact with the fibre, the developments and modifications of which constitute the whole art of dyeing.

1. By the first method, which is by far the most common, the fibrous matter is separately impregnated with the mordant, which is by various means decomposed, so as to deposit its base in an insoluble state upon or within the fibre, and afterwards the colouring matter is applied. Take, for example, the case of dyeing a common black from logwood upon calico, which has no affinity for the colouring matter of the logwood. The first process is to pass the calico through a hot aqueous solution of sulphate of iron, sometimes mixed with acetate of iron, and to remove the excess by passing the cloth through rollers; the cloth, either previously dried or not, is then passed through a mixture of lime and water which has the effect of decomposing the iron salts and liberating oxide of iron. A washing in water to remove the excess of lime or any loosely attached oxide of iron prepares the calico for coming into contact with the logwood. The calico, which has now a buff colour, owing to the attached mordant of oxide of iron, when placed in a hot decoction of logwood speedily acquires a dark hue and in about half an hour has become dyed of a dense black colour, and, when smoothed and finished, forms the common black calico of the shops. A variety of other cases might be adduced; woollen cloth boiled for some time in bichromate of potash solution acquires a certain amount of a salt of chromium, which enables it to take a black colour from logwood, and other colours from other dye-stuffs. Woollen, boiled with salts of tin, is enabled to dye up a brillant scarlet in decoction of cochineal; boiled with alum, it will take a great variety of colours in various dye-stuffs. The practice of calico-printing illustrates in a very forcible manner the action of mordants; by the aid of apparatus described in the article upon that subject, portions of a piece of calico are impregnated with mordants, and these portions alone acquire colour from the dyeing solution, and thus designs or patterns are produced upon a white ground. The most usual method of impregnating the fibrous matter with mordant, consists in heating it with the required metallic salts, and it will be seen hereafter that easily decomposed salts are those preferably used; or substances such as chalk, alkalies, or tartar are added to some more stable salt, such as alum, to induce the formation of comparatively unstable compounds, which, under the influence of a high temperature and contact with fibrous matter undergo decomposition, the metallic oxide or some basic insoluble compound of it becoming intimately combined with the fibre, which is then said to be mordanted.

2. A second method, less general than that above described, is to apply the colouring matter before the mordant. It is resorted to only with heavy goods which absorb a large quantity of liquid, or with light colours upon other fabrics; dyes produced in this way are superficial in their character, and not so permanent as those produced by the first method. In dyeing by that method it is in many cases customary to add a small quantity of mordant to the dye-bath when the process is quite or nearly finished, or to pass the dyed goods, as a final operation, through a diluted mordant.

3. A third method is to apply the mordant and the colouring matter together to the fibrous substance. In common piece-dyeing dency to form insoluble lakes in the solution, which, depositing only in weak liquids this plan is seldom followed, on account of the tenon the external part of the fibres, give inferior results, alike as to sta bility of colour, depth of shade, and evenness or regularity of the dye. In calico printing or in padding, this method is of extended application and the inconveniences experienced in common dyeing are ing salts and the use of thickening matter. Lakes are very probably not perecptible, owing to the greater concentration of the mordantformed to some extent during the preparation of the mixtures, but, the combination taking place in the presence of a fluid made viscous with gum or starch, the insoluble lake is in an extremely fine state of division; in such a mixture there is always present an acid or an acid salt, such as acetic acid, oxalic acid, tartaric acid, or alum, chloride of tin, cream of tartar, or binoxalate of potash. These tend, in the first instance, to restrain the formation of a lake, and afterwards, when the fibre and the mixture of mordant and colouring matter are submitted to heat, as in the process of steaming or stoving, facilitate the solution of any lake formed, which thus finds entrance into the fibrous matter, and there undergoes combination with it,

owing to decomposition of the mordanting salts, a true dyeing taking place.

PRACTICAL DYEING PROCESSES.

By the foregoing preliminary observations the reader will have been prepared to comprehend the rationale of the practical processes of dyeing. In order to give a fairly comprehensive account of these, it has been found convenient to take the colours in the old arrangement of simple and compound colours. Red, blue, and yellow are supposed to be simple or primitive colours; the methods of obtaining these being given, then follow the colours from mixtures of two of the elementary colours, as green from yellow and blue, orange from red and yellow, and purple from red and blue. The colours not included in the above, and in the dyer's philosophy made by mixing the three elementary colours, red, blue, and yellow, in different proportions-namely, the browns, greys, and chocolates, and black-will be conveniently treated of after those supposed to result from the mixture of two of the primary colours.

This arrangement, though perfectly arbitrary, is both convenient and consistent as far as regards dyeing; for though modern discoveries in optics may show that pure blue and yellow do not make green, and may in other respects disturb the older ideas concerning primitive and secondary colours, yet the dyer has sufficient justification for retaining the old system, because he can show that his blue and yellow always make green, and that the proper mixture of the so-called simple colours produces a compound shade which can be calculated beforehand from the proportion of the respective colours employed.

Red upon wool from cochineal.-Let it be assumed that the shade of red required is fine scarlet, such as is worn by officers of the British army, and that the woollen cloth is of finest quality. The cloth first requires purifying from all the adventitious substances which it has acquired in the process of manufacture, in order to prevent irregularity and unevenness in the shade of colour; this is done by methods described in the article BLEACHING. The only materials required to produce a fast scarlet upon wool are oxide of tin and the colouring matter of cochineal, but it requires much practical skill to bring them into contact properly. After the cloth is cleaned, and while it is still wet from its last washing, it is mordanted by boiling it in a solution of a salt of tin with or without cream of tartar. The parts of the boilers not in actual contact with the fire are frequently constructed of pure block tin, or at least all parts out of water should be of this metal, or else protected by wood, or the dyeing vessel should be made entirely of wood and heated by steam pipes; for if the cloth containing the acid solution of tin comes in contact with a copper or brass surface it acquires a stain which afterwards dyes up an impure colour. What takes place in the course of boiling is that eventually a certain portion of tin, probably in the state of stannic oxide, becomes fixed upon or within the fibres of the wool, and this in a perfectly uniform manner. The tin not in intimate combination with the wool, or held merely by capillary attraction, is washed off by water before the cloth is brought into contact with the colouring matter.

The mordanted cloth is now brought into a boiler containing finely ground cochineal diffused through a sufficient quantity of water. to which it is usual to add some more tin mordant and tartars the cloth is turned continually to prevent folds or creases from interfering with the free access of the dye to all parts of it. The contents of the boiler are heated to the boiling point, and in half an hour or so the liquid becomes nearly colourless, and the aloth is found dyed of a-bright red.

The above may suffice to furnish a general view of the procedure usually followed, and to illustrate the principles involved with regard to numerous other dyes besides cochineal. To give the general reader a further idea of certain operations practised in the use of that colour (and the description applies more or less to

others), the following particulars may be noted.

The tin mordant used for scarlet on wool.-It is now 200 years since the discovery was made of the use of tin with cochineal for dyeing scarlet; it might be thought that by this time the exact kind and quantity of tin solution to be used would have been settled; there exists, however, the greatest diversity upon this point among practical dyers. The two salts of tin met with in commerce, designated by chemists stannous and stannic chlorides, have received various names from dyers. Crystallized stannous chloride is generally known as "tin crystal;" the solution of the same as also distinguished, the difference being in the degree of concentration; muriate of tin. A single muriate and a double muriate of tin are

but in some parts of the country double muriate of tin is the name given to a solution of stannic chloride, elsewhere called bichloride of tin, and a good deal of confusion is sometimes caused by the various uses of the trivial names of the solution of tin. Experi ence teaches the dyer that there are scarcely two dye-works in the world in exactly the same condition with regard to either water and air, or apparatus, or quality of materials, and that the nature and quantities of drugs, mordants, and dye-stuffs used, and the duration and temperatures of the operations which secure admirable results in one that by far the greater part of the variations introduced by practical place are altogether unsuitable in another. It is, however, clear dyers are not really founded upon necessity. Thus although the best colours can be obtained by the use of simple tin solutions manufactured on the large scale, in nine cases out of ten the operative dyer that he employs special methods aud preparations without which it of scarlet insists upon preparing his own solution, and pretends would never be fit to use; and hence a countless number of tin solutions are in use.

for many other colours upon wool, silks, and cotton, are commonly Tin spirits.-The solution of tin used by dyers for the scarlet and called spirits, or "tin spirits," a name which is very old, and appears to have originated in the use of nitric and hydrochloric acids to dissolve the tin, which acids were formerly, and are even at present, called spirits of nitre and spirits of salts. One solution which is a favourite, nitrate of tin (sometimes called "bowl spirits," from being prepared from the ease with which its metal goes to the wool, is the so-called in an earthenware bowl) made by dissolving thin metallic tin in moderately strong nitric acid. This is an operation requiring great care and some experience to prevent the formation of insoluble metastannic acid; the tin is added by small portions and gradually, so that the acid does not become hot; the solution takes place quietly, inodorous nitrous oxide is evolved, and ammonia is formed. If the tin be added too rapidly to the acid, red fumes of nitric oxide are evolved, the liquid boils up, becomes thick from separation of metastannic acid, and is utterly useless as a mordant. This so-called nitrate of tin is a very unstable compound, decomposing spontaneously in a few days, so that it has to be prepared just as it is wanted; it is therefore not an article of commerce. The other very numerous "tin spirits" may be said to be solutions of tin in a mixture of nitric and hydrochloric acids; but the latter acid is sometimes replaced by the chlorides of sodium and ammonium, the resulting mordant being essentially a stannic chloride mixed with stannous chloride. Closely woven and loose woollen fabrics, such as yarn and flannel, require different tin mordants, as some mordants are more quickly decomposed than others. The result of using an easily decomposable mordant such as the nitrate of tin upon closely woven cloth would be the formation of a deposit upon the external fibres of the wool, the interior of the cloth being unaffected. For such cloth, therefore, a tin spirit which is only slowly decomposed, such as the muriate alone or mixed with tartar, must be chosen, so as to allow of a tolerably thorough saturation of the cloth before the breaking up of the mordant during the boiling. Here it may be observed that good, thick, and finely woven cloth which is dyed in the piece, that is, after weaving, is hardly ever completely dyed through; this can easily be shown by cutting through the cloth with a sharp knife, when the interior will be seen sometimes nearly white and generally much paler than the exterior; hence the preference which is given to cloth madə from yarn dyed before weaving, the colours of which do not fade so readily as those of piece-dyed goods. Imperfection in the dyeing of the latter can by care, however, be reduced to a minimum, and in dark goods is hardly discernible.

Use of tartar along with tin mordant.-The "tartar" of the dyer is a more or less impure form of the cream of tartar of the shops, or the acid potassium tartrate of chemists. It is in very general use for wool dyeing, and when employed with dye-stuffs plays the part of an acid, and could in fact be replaced by an acid; in other cases, when used in mordanting, it no doubt acts as a salt, contributing to neutralize the strong mineral acids of the mordant, and rendering them more ready to decompose in the presence of the cloth. In a particular receipt for dyeing scarlet the proportions of materials are

as follows:-20 of tin solution, containing about 20 ounces of metallic tin dissolved in nitric acid, with the addition of a little common salt, are used to 100 lb of woollen cloth. Of the 20 lb of mordant, 13 b are taken and mixed with a solution in water of 8 ib of crude tartar, and about 8 ounces of cochineal are added to enable the dyer to form a judgment of the progress of the mordanting. The ingredients having been boiled for a couple of hours, the cloth is rinsed in clean water and placed in another boiler, containing the residual 7 lb of mordant and 6 lb of ground cochineal, which are sufficient to dye up a full scarlet colour; but if the scarlet is required to be very bright, or what is called "fiery" coloured, a further quantity of tartar is added; this has the effect of somewhat reducing the depth of colour, and at the same time giving it a yellowish or orange hue, which for certain purposes is much desired. Use of yellow in scarlet.-It appears that Bancroft, who wrote about the end of the last century, was the first to suggest that the bright fiery scarlet, which the dyers found they could best obtain by using a large quantity of tartar, might be produced more cheaply by adding some yellow colouring matter to the cochineal, or by first dyeing the cloth a light yellow; he tried the yellow from quercitron bark, and succeeded as far perhaps as was possible with that material. At any rate from his time it has been customary for dyers who do not aim at the highest degree of excellence in the scarlet colour to use a purified preparation of quercitron bark, commercially known as flavine, in conjunction with cochineal; other yellow colouring matters, such as fustic and turmeric, are also used. An admixture of these substances cheapens the cost of the colour, which can be made nearly equal in appearance to that obtained with cochineal alone, but it does not stand wear so well, and is more readily stained by various influences. The best scarlets are still dyed exclusively with cochineal.

Scarlets on wool from lac-dye.-The colouring matter of lac-dye is in its chemical properties and composition very similar to, if not quite identical with that of cochineal. As it is imported into this country from India, it is, however, less pure than average qualities of cochineal; and it is probably on account of its impurities that the dyer cannot obtain quite so good results as the best cochineal colours, although if skilful he may approach them very closely. Having been submitted to a preliminary treatment with acid to free it from alumina and other earthy matters used in its preparation, it is then applied exactly in the same way as cochineal. It is extensively used for a second class scarlet, and is believed to be somewhat more durable and stable even than cochineal. The red cloth so much used for military dress is reputed to be prepared mainly with lac-dye.

Crimson red on wool.--This colour is also dyed with cochineal, but with a mordant of alum instead of tin. It is a far less important colour than the scarlet, and compared with it is dull and flat; it is, however, rich and durable, and combines excellently with other colours.

The mordanting of cloth by means of alum, an operation of capital importance for a large series of colours derived from all varieties of dye-stuffs, must now be noticed.

Aluming of wool.-The method of mordanting with alum, generally called aluming, is practically a simple process, but the chemical principles involved have given rise to much debate amongst experimenters. The aluming is usually performed by boiling the wool for one or two hours in a solution of common alum mixed with tartar; a certain portion of alumina, or, it may be, of some compound of aluminium, becomes thus intimately combined with the wool, and forms a basis upon which a coloured lake may be produced with solutions of colouring matters. The chemical conditions are somewhat different here from those which obtain in the case of mordanting with tin; for the disposition of tin salts in dilute solutions to decompose even spontaneously is so manifest that it may readily be supposed that some action on the part of the wool takes place which induces the formation of oxide of tin. The great apparent stability of alum caused the explanation of its action given by Thenard and Roard to be for a long time accepted. They held that it was absorbed whole or unchanged by wool, which retained it by some undefined power, so that it could not be removed by cold water, and required to be heated twenty times with boiling water to dissolve it out. In the light of modern researches this explanation may be safely rejected as erroneous. What appears to be the true state of the case was mainly brought out by experiments of Havrez, suggested by the celebrated Belgian chemist Stas, and supported by further knowledge of the properties of alum discovered by Tichbourne and Naumann. In fact, alum, contrary to what was formerly thought, is particularly liable to decomposition, even when not in contact with fibrous matters which might possibly have an influence upon it. Naumann has shown that by simply heating a solution of alum, saturated in the cold to its boiling point, an insoluble basic compound is soon produced, so that, after prolonged heating, as much as 25 per cent. of the alumina is precipitated, and the liquid is found to have become acid. Beyond this fact it is proved that wool when placed in a solution of alum, containing pure sulphuric acid, has the property

of absorbing more acid than alum; this unequal absorption is attri buted by Havrez to a kind of dialysis, which, together with the tendency of the alum to decompose, sufficiently explains the deposition of alumina upon the wool. The action of tartar in aluming, according to the same authority, is that of an acid salt, and its addition influences the nature of the mordant deposited in the same way as if an excess of alum were present, or as if other acid bodies, such as sulphuric acid, oxalic acid, &c., were added. The insoluble aluminous compound which separates from solution of alum on prolonged boiling in a glass flask could not act as a mordant, being indifferent or passive to colouring matters; when deposited on fibrous matter it does not adhere, but can be washed off, or when dry may be shaken off like dust; this, therefore, is not the alumina mordant, nor do the researches of Havrez really point out what the alumina mordant is, though they are valuable and suggestive as showing under what conditions either a basic or an acid aluminous deposit is formed. With the former, which is unfavourable for dyeing, a blue colour is given with logwood, and a purplish red with Brazil wood; with the latter, the wool dyes up a violet with logwood, and a purer red with Brazil wood. The basic state of the aluming results, it is supposed, from the deposition of hydrate of aluminium upon the wool, and is caused by having too little alum or too much water, by boiling for too long a time, or by the use of salts which have a neutralizing action upon the alum. It is easily induced, when the weight of wool is more than 15 times greater than that of the alum. In other circumstances the acid state results, in which the wool is said to fix first hydrate of alumina, and also hydrated sulphuric acid from the sulphate of alumina. These conclusions of Havrez cannot, however, be accepted as final or satisfactory; and there is still much to learn upon the principles of aluming and mordanting generally.

The wool being successfully alumed acquires a crimson colour by dyeing in cochineal, but, as before stated, this shade is not of much value.

The shades of red between scarlet and crimson reds proper, or cherry reds, are also dyed with tin mordant and cochineal in nearly the same way as the scarlet; but in order to avoid a yellowish tone, the natural cochineal may be mixed with the manufactured or modified material known as ammoniacal cochineal.

Ammoniacal cochineal.-This is made by treating ground cochineal with concentrated aqueous ammonia for several days; the colouring matter undergoes important changes by this process, an amide is formed, and the effect upon the colouring matter is that tin mordants give with it no longer a scarlet, but rather a violet tone. Ammoniacal cochineal is much used in fine dyeing for pinks; and according to the proportion in which it is added to ordinary cochineal, the normal scarlet shade is gradually brought over to the red and even to the crimson.

Pink or rose colour upon wool.-This shade is obtained from ammoniacal cochineal, mordanting previously in a mixture of tin solution, alum, and tartar; the quantity of tin mordant used is small, the alum being the essential basis.

Other red colours upon wool.-The, colours mentioned above are from cochineal or its congener lac-dye; there are several reds obtain. able from other colouring matters, which, though less important, are still worthy of mention.

Madder red upon wool.-This colour is wanting in brightness, but it is valuable for its stability, and has at times been largely used for common red military cloth. As a basis for browns, chocolates, and other dark colours, it is very suitable when its com paratively high cost is not an objection. To obtain madder red, the wool is boiled for two hours with a mixture of alum, tartar, and tin salt,-3 lb alum, 1 tb tartar, and 4 ounces of the tin solution being taken for 10 b of cloth; after boiling, the cloth is rinsed in water to remove uncombined mordant, and then dyed with madder, or preferably its derivative garancin, with addition of a portion of tartar; the dyeing may be accomplished in an hour, the depth of colour varying with the amount of colouring matter used.

Artificial alizarin on wool.-By employing artificial alizarin somewhat better shades of colour can be obtained, and even pink colours of much solidity produced. A process for obtaining a fast red on woollen yarn, from alizarin, is as follows:-boil 10 fb wool for an hour and a half with 1b sulphate of alumina and Ib tartar; rinse in water, and then dye with 6 to 7 ounces of artificial alizarin paste containing 10 per cent. of dry matter; commence the dyeing cold, and gradually heat to boiling. Alizarin can be used as a basis for producing fast brown shades, by adding fustic and extract of indigo after the red has been developed, and if necessary, a further quantity of sulphate of alumina and tartar.

Red colours can also be obtained by using Brazil wood or other red woods instead of madder; they are, however, of a low class and seldom employed. Archil alone, without mordant, can yield a full crim son upon wool, but it is not very stable, and is, moreover, expensive.

Aniline reds upon wool.-There are several artificial red dye-stuffs, which may be used for wool, but none possesses great excellence. The only one which resembles cochineal in its qualities is the recently discovered eosine; this, with an alumina mordant, gives upon wool a very good imitation of cochineal scarlet, but an imita

Red colours on cotton.-Turkey red.-Cochineal, which is so able a colouring matter for wool, does not dye satisfactory colours upon vegetable fibres; but from very remote times the Hindus have possessed a process for dyeing a brilliant and extremely permanent red upon cotton fabrics by means of madder. This process travelled westward through the Levant into Turkey and Greece, the date of its introduction into Western Europe going no further back than the middle of the 18th century, at which period Greek dyers were induced to settle in France and make known the methods in use for the production of this much desired colour. The name Turkey red, or Adrianople red, was applied to calico dyed with it at the time that such goods could be obtained only from the East, and it still retains the name. So much was the colour esteemed that in 1765 the French Government circulated a pamphlet describing the best known methods of dyeing it on yarns, and some years afterwards, the British Government paid a sum of money to a Frenchman named Papillon, for disclosing the whole process of obtaining it. The dyeing of Turkey red upon cloth and yarn is now extensively carried on in Great Britain, and with great success. Turkey red is essentially a madder red with an aluminous basis, but differs from a common madder red by containing oil, and it is the fixing and combining of the oil with the fibre and the colour which constitutes its peculiarity. Divested of details the process of producing Turkey red may be divided into four stages: (1) the oiling of the cloth; (2) mordanting with a salt of aluminium; (3) dyeing with madder, or its equivalents garancin or alizarin; and (3) the brightening of the dyed colour. The preparation of the cloth with oil is a process used in no other kind of dyeing; of its utility there can be no doubt, but all the attempts of chemists to explain the rationale of its action have failed. There are many modifications of the method of applying the oil, but the older and more commonly used process is to mix the oil with a dilute solution of potash or soda ash, so as to diffuse it uniformly through the liquid, forming an emulsion; the oil is not dissolved by the alkalies, nor is it supposed to combine with them, but is simply held in a state of excessively fine mechanical division. A low quality of olive oil is most generally used in Europe, that from Mogador, in the north of Africa, being very suitable. Certain kinds of oil do not answer for Turkey red, only those being suitable which, probably from containing free fatty acids or albuminous matters, readily form a milky emulsion with weak alkaline solutions; other kinds are, however, in use in some places. The cloth to be dyed is steeped in the oily emulsion, wrung out, and dried in a warm stove; this process is repeated six or eight times, and the cloth is finally washed in weak alkali to remove from it all the oil not intimately united to the fibre. The result of this treatment, which is the most delicate and important in the Turkey red process, is that the cloth becomes impregnated with a fatty matter, which by the contact of alkalies and heated air has undergone some change from its original state, which is usually called an oxidation, but the nature of which is really unknown. The cloth now possesses a power of attraction for mordants and colouring matters greatly superior to untreated cloth; and further, its physical condition is changed so that colours upon it are more transparent and more vivid than upon ordinary cotton.

The cloth in this state is ready for mordanting, which is done by passing it through a bath of alum, partly neutralized with carbonate of soda or by chalk, or in a bath of acetate of alumina, the object being to obtain a regular deposition of the aluminous base the fibre; the excess of mordant is carefully washed away from the cloth, which is now ready for dyeing.

upon

The dyeing is accomplished in the ordinary way, by keeping the cloth in continual motion in a vessel containing heated water and the dye stuff, which may be madder, garancin, or artificial alizarin. It is a very general practice to add a quantity of ox-blood to the water used in dyeing Turkey red. What purpose this fulfils is not known; its colouring matter cannot be supposed to be of any use; its albuminous constituents may have some useful action, but this seems very doubtful; probably its addition is quite superfluous, and is retained from older times, when dyeing was less understood than at present. When the dyeing is completed the colour is a full and deep but-dull red, which requires brightening. The brightening operations consist in removing brownish matters from the dye by boiling in soap and alkalies. To give a still more brilliant colour, the goods are boiled for several hours in a closed copper boiler with a mixture of salt of tin with the soap used in the last process of brightening, occasionally under a pressure greater than that of the atmosphere, in order to obtain a temperature some degrees higher

than 212° F.

In many processes of Turkey red dyeing, the cloth is treated with decoction of gall-nuts, or with sumach, after the preparation with oil and before the mordanting; this enables it more easily

Barwood red.-An imitation of Turkey red is obtained from barwood; it is much inferior both in beauty and stability to the real colour, but the ease with which it can be dyed, and the less costly nature of the materials employed, enable it to be sold at a much lower price, and for some purposes it is largely used. Bar wood is one of the red dye-stuffs of which the colouring matter is very slightly soluble in water; it is used in a state of fine powder. The cotton to be dyed is impregnated with a tin mordant by any of the means known to dyers, and then boiled with the dye-stuff; the colouring matter as it dissolves is fixed by the mordant, and the process is continued until the required shade is obtained. This wood, and a similar material called camwood, are also employed in woollen dyeing to give brownish reds, and to dye a "bottom" or foundation for indigo blue colours, by which some economy in indigo is effected, and a peculiar bloom on the blue is produced. The class of woods represented by Brazil wood, do not yield good reds upon cotton.

Blue Colours.

The most important of the blue colouring matters is indigo. This may be said indeed to be the most important of all colouring matters, both as regards the large quantity and monetary value of what is produced and sold, and the permanence and solidity of the dyed colours which it yields. The indigo dye is a manufactured article, prepared in the place of growth. of the plant which produces it. The indigo plant could itself be used for dyeing, but from 200 to 250 b of it would be required to produce the effect of a single pound of the prepared indigo. In England, and many other countries possessing a temperate climate, the species Isatis tinctoria, or woad, has been cultivated, and has been used from time immemorial for dyeing blue. Its comparative poverty in colouring matter has caused it long since to be disused by dyers as a source of colour; it is, however, employed by them in the preparation of their indigo vats, but rather as a convenient material to induce fermentation than as a dye.

Indigo is distinguished from nearly all other colouring matters by its complete insolubility per se in water and other ordinary solvents. It dissolves to a very slight extent in heated aniline, petroleum, and acetic acid, which upon cooling redeposit it; the only real solvent for it is anhydrous acetic acid mixed with a little sulphuric acid, from which water precipitates it unchanged, but this solvent is inapplicable in dyeing. But solubility is an essential condition for dyeing, and means have been found to obtain satisfactory solutions of indigo by circuitous methods and a change in its chemical composition. By various which involve the temporary destruction of its blue colour deoxidizing agents, indigo blue can be changed into a white substance, indigo white, which dissolves with facility in all alkaline liquids, forming a colourless or slightly yellow solution. On exposure to the air or other sources of oxygen, the solution yields the insoluble blue indigo, and permanently dyes any fibre which has been saturated with it.

This is the only case in which such a method of dyeing is applicable, and on that account it possesses much interest. We shall now proceed to describe some of the practical methods in use for indigo dyeing,

Fermentation process.-The oldest of these, and one naturally suggested by the method employed in preparing the dye-stuff, is the process of fermentation in contact with lime, or sometimes soda or potash. During this process, gaseous or liquid substances are formed, which have the power of reducing indigo from the blue to the white state, and fitting it for dyeing. This ancient method has not been superseded in England at least, being employed at the present day for nearly all woollen goods dyed with indigo, the consumption of which is greater for woollen than for all other kinds of cloth

The woad vat.-To a course of lectures upon dyeing, recently delivered by Mr Jarmain before the Society of Arts, we are indebted for the substance of the following account of the woad vat used by the Yorkshire dyers. The materials employed are indigo, woad, madder, bran, and lime. For this process as for every other in which it is employed, the indigo must be reduced to the finest possible powder. It is generally ground mixed with water, in closed revolving castiron cylinders containing iron rollers or balls, for several days, or until the slime or pulp formed contains no visible particles of the dye-stuff. The proportions of materials employed are:

The woad is first placed in the dyeing vat nearly filled with water, which is heated to between 140° and 150° F.; after some hours (required to soften the woad), the bran, madder, and indigo are added, and half of the whole quantity of lime. In a few hours, if all is right, signs of conimotion produced by fermentation will be visible, the liquid will become greenish, and a blue scum will be visible on the surface; a piece of wool is put in as a test, and if in a short time it becomes dyed blue the process is proceeding well; a little more lime is added, but at intervals, so as not to check the progressing fermentation, and, if it should become necessary, the vat is heated up by steam to its original temperature; on the third day the vat should be ready for dyeing. Such a vat as this requires skilful management to control the fermentation; without lime the reduced indigo would not be dissolved; with too much lime the fermentation would be stopped. The woad acts as an easily fermentable matter, and furnishes a portion of blue colour; the bran also no doubt is useful, on account of the ease with which it begins and promotes fermentation; the madder is probably of no use at all, its employment being still continued from an old unfounded notion that it gives some of its red colouring matter to the indigo-dyed goods, for the small amount of saccharine matter present in 2b of madder cannot be held of any importance in the presence of 5 cwt. of woad.

A woad vat, when ready for dyeing, consists of a certain depth of a tolerably clear solution of white indigo in lime, and a somewhat voluminous semi-solid mass at the bottom, consisting of the bulk of the woad, the excess of the lime, the insoluble part of the madder, and the impurities always present in indigo. To keep the cloth to be dyed from contact with the muddy bottoms an iron hoop, of the internal diameter of the vat, covered with a network of open meshes is lowered into it and secured at a safe distance from the bottom.

The pieces to be dyed, after being well cleansed, are placed in the liquor, and kept in constant movement to insure full access of the colour to all parts. The time required to dye, varying from 20 minutes to two hours, will depend upon the fineness and weight of the cloth, and upon the depth of colour required; if the goods require it, they are dyed a second time. In moving the pieces about, they must not be brought above the surface of the liquid, for the oxygen of the air would restore the dissolved white indigo to its blue insoluble state. When the pieces are found to be sufficiently impregnated with the dye, they are withdrawn from the vat; at the moment of leaving the dyeing liquor they are seen to be of a yellowish colour, which almost instantly changes into a bright green, then darker green, and finally becomes blue through the absorption of oxygen by the white indigo. Loose wool or yarn is dyed by inclosing it in an open and movable network bag.

The vat above described can of course dye only a limited quantity of material, becoming after every operation poorer in indigo; but it is not necessary to re-set a vat. The strength of its contents is kept up by constant additions of indigo, lime, and bran; no more woad is added, the quantity used at first being sufficient for about its own weight of indigo.

Bran and molasses vat.-Another kind of indigo dye vat, very extensively used on the Continent, and highly spoken of by practical men, is prepared as follows. A vat 6 feet in diameter and 7 feet deep is filled with water warmed to 130° F.; then 44 lb of ground indigo, 34 lb crystals of soda (or instead 16 lb soda ash) and 67 lb of bran, and twelve hours afterwards 2 b slacked lime, are added; in 24 hours the indigo should commence to be dissolved, and a test strip of stuff plunged in the liquid should be speedily dyed, but some hours longer and the gradual addition of 18 or 20 lb more of lime are required to bring the liquor into its best condition. In this vat, as in the woad vat, the lime controls the fermentation of the bran, and has to be added with care. With each pound of indigo added to replace what has been removed from the vat during a day's dyeing fb of molasses and crystals of soda and 3 or 4 fb lime must be used. By daily replenishing the vat it can be used continually for four or five months; at the expiration of that time the bottoms must be removed; the supernatant liquor containing indigo in solution may be used instead of water for setting a fresh vat.. This vat is said to have quite supplanted the old woad and madder vat, molasses beng preferable on the score of cheapness and also of solubility. I

80 to 90 lb dry slaked lime.

These materials are well mixed together and raked up at intervals for say 24 hours, when the vat is ready for use. The lime decomposes the salt, liberating ferrous oxide, which acts upon the indigo, converting it into white indigo, which dissolves in the lime water. In large establishments for dyeing calico blue, it is usual to have a series of such vats in a row; the pieces to be dyed are tightly stretched on a frame and dipped in the liquid for from seven to ten minutes, after which they are believed to be as fully saturated as possible; the frames are next raised into the air, and in a few minutes the blue colour becomes developed; the same process is then repeated until the required depth of colour is obtained. By printing certain resisting compositions on the cloth previous to the dipping, white figures can be obtained upon a blue ground, producing what is known as the navy-blue style of print, formerly much worn by the lower classes in England. By combining suitable mordants with the resisting composition, not only white, but orange, yellow, and green coloured figures can be obtained upon the blue ground; but the production of these is rather a branch of calico printing than of dyeing proper.

Although this kind of vat is most generally used for the lighter qualities of calicoes, it can also be applied to such woollen goods as merinoes, which are not very closely woven, and also to silks. Hydrosulphite of soda vat.-In 1871 Schützenberger and Lalande introduced a new reducing agent applicable to indigo dyeing, the so-called hydrosulphite of soda, obtained by acting upon acid sulphite of soda with metallic zinc. It possesses the most energetic deoxidizing powers, and in the presence of alkalies almost immedi ately reduces and dissolves indigo. It has been applied both in dyeing and in printing indigo colours, but cannot be said to have succeeded in displacing the older kinds of vats, having the disadvantage of costing much more without producing any apparent improvement in the colour yielded.

By preparing a very strong indigo vat, and thickening the fluid with gum, it is possible to print indigo blue colours in designs, but the many difficulties attending the process have very much restricted its application.

The colour yielded by indigo, though far from brilliant, is extraordinarily permanent, and is much used for articles intended to withstand much wear and rough usage, and also as a basis for the best quality of black upon fine woollen cloth.

Sulphate of indigo.-When indigo is acted upon by concentrated sulphuric acid it forms a solution of the so-called sulphate or extract of indigo, which, though possessing an intensely blue colour, cannot by any means be made to furnish the original dye. This preparation of indigo is applied only in wool and silk dyeing; it gives blues which are tolerably bright, but possess none of the stability of those obtained from real indigo. For vegetable fibre it has no affinity whatever either with or without mordants.

Prussian blue.-This, perhaps the earliest of artificial dye-stuffs, was accidentally discovered in 1710, though not used in dyeing for some time afterwards. The simplest method of employing it consists in first impregnating the material to be dyed with peroxide of iron, and then passing it into a solution of yellow prussiate of potash acidified slightly with sulphuric acid. Prussian blue upon silks is thus dyed. The most convenient way of obtaining a deposit of the oxide of iron consists in soaking the silk in a somewhat strong solution of the ordinary dyers' nitrate of iron; in the course of two or three hours a certain quantity of the oxide is found to be intimately combined with the silk; the excess of nitrate is then washed away and the silk worked in the acidified prussiate bath, when it immediately assumes a light azure shade; by repeating the treatment several times any depth of colour may be obtained.

Calico can be dyed in the same way, but both for that and for silk it is usual to add to the iron solution a small quantity of salt of tin, which is useful in giving a purplish tone to the blue and preventing the production of a disagreeable greenish tinge.

A deep colour cannot in this way be satisfactorily given to woollen, for which a treatment is adopted depending upon a decomposi tion of the prussiate by means of heat and acids. For dyeing say 110 I of merino the following proportions and methods may