The dyeing of wool. The only real difficulty is to make substances retain the colours after the matter has been imbued; because being admitted so readily into their undilated pores, the particles cannot be afterwards compressed and retained by the contraction of these pores, as is the case with wool. It requires double the quantity of cochinell which is necessary for wool to communicate a crimson colour to silk; a certain proof that it can take up a greater quantity, and consequently that the pores are sufficiently large and accessible. Unbleached cotton is always preferred for dyeing Turkey red, because in this state the colour is found to be most permanent; and this is ascribed to the pores or interstices being less open than after it has undergone the process of bleaching. The same thing is observed of raw or unscoured silk. It is found to combine more easily with the colouring matter, and to receive a more permanent colour in this state, than after it has been scoured and whitened. "The openness of cotton and linen," says Dr Bancroft, "and their consequent readiness to imbibe both colouring particles and the earthy or metallic bases employed to fix most of them, are circumstances upon which the art of dyeing and calico-printing is in a great degree founded." But is not this too mechanical an explanation of the phenomenon? Might it not rather be alleged that it is owing to a difference of affinities which exists between the particles of colouring matter and the substance which is separated from the silk or cotton by the process of bleaching or scouring? This substance probably acts the part of a mordant; and having a stronger affinity for the stuff and for the colouring matter than the stuff has for the latter, the colour communicated is more durable when silk or cotton is dyed in the unbleached or unscoured state.

To prepare cotton stuffs for receiving the dye, several preparations are necessary. It must first undergo the process of scouring. By some it is boiled in sour water, or dyeing in alkaline ley. It should be kept boiling for two hours, then wrung out, and rinsed in a stream of water till the water comes off clear. The stuffs to be prepared should be soaked for some time in water, mixed with not more than 1/4th part of sulphuric acid, and then carefully washed in a stream of water, and dried. In this operation the acid combines with a portion of calcareous earth and iron, which would have interrupted the full effect of the colouring matter in the process of dyeing.

Aluming is another preliminary process in the dyeing of cotton. The alum is to be dissolved in the manner already described in preparing silk. Each pound of cotton stuff requires four ounces of alum. By some a solution of soda, about 1/4th part of the alum, and by others a small quantity of tartar and arsenic, are added. The thread is to be impregnated by working it in small quantities with this solution. The whole is then put into a vessel, and the remaining part of the liquor is poured upon it. In this state it is left for twenty-four hours, after which it is removed to a stream of water, and allowed to remain for an hour and a half, or two hours, to extract part of the alum. It is then to be washed. By this operation cotton is found to gain an addition of about 1/5th part of its weight.

The operation of galling is another preparatory process in the dyeing of cotton stuffs. The quantity of astringent matter employed must be proportioned to its quality, and the amount of the effect required. Powdered galls are boiled for two hours in a proportion of water, regulated by the quantity of thread to be galled. This solution being reduced to such a temperature as the hand can bear, is

Sect. III.—Of Cotton.

Cotton is the down or wool contained in the pods of a shrubby plant, which is a native of warm climates. Of this genus of plants (Gossypium, Lin.) there are four species, one of which only is perennial; the other three are annual plants; but of these there are many varieties, occasioned by the difference of soil or temperature in which they are produced. The principal differences among cottons consist in the length and firmness of the filaments, and in their strength and colour.

The peculiar structure of the fibres of cotton is not well known. According to the microscopic observations of Leeuwenhoek, they have two sharp sides, to which are ascribed the irritation and inflammation of wounds and ulcers when they are dressed with cotton instead of lint. This peculiarity of structure, it is also supposed, may occasion some difference in the conformation and number of the pores, on which alone the disposition of cotton to admit and retain colours better than linen seems to depend. In this respect, however, it is inferior to wool and silk, because, on account of its vegetable nature, its affinity for colouring matter is less powerful.

It is well known that silk, cotton, and linen have a weaker affinity for colouring matter than wool. Le Pileur d'Apigny attempts to explain this by supposing that the pores of these substances are smaller than those of wool, and that the colouring particles enter them less easily and freely. But according to the observation of Dr Bancroft, the reverse of this seems to be the fact; for there is little difficulty in making silk, cotton, and linen imbibe colouring matter, even when it is applied cold, without any artificial dilatation of the pores, which is always necessary in Substances divided into a number of equal parts, that the thread may be wrought pound by pound. The whole stuff is then put into a vessel, and the remaining liquor poured upon it, as in the former process. It is then left for twenty-four hours if it is to be dyed black, but for other colours twelve or fifteen hours are found sufficient. It is then wrung out and dried.

In the galling of cotton stuffs, which have already received a colour, the precaution should be observed of performing this operation in the cold, otherwise the colour is subject to injury.

Berthollet informs us, that cotton which had been alum-ed acquired more weight in the galling than that which had not previously undergone that process; for although alum adheres but in small quantities to cotton, it communicates to it a greater power of combining both with the astringent principle and with the colouring particles. This, we may add, may be considered as a good instance of the action of intermediate affinities, and of the advantage to be derived to the art of dyeing, from investigating and observing this action.

**Sect. IV.—Of Flax.**

Flax and hemp nearly resemble each other in their general properties; and, so far as relates to the process of dyeing, what is said of the one may be applied to the other. Flax or lint is obtained from the bark of *Linum usitatissimum*, and hemp from that of *Cannabis sativa*.

Before flax is properly prepared to receive the dye, it must be subjected to several processes. One of the most important is that of watering, by which the fibrous parts of the plant are separated, and brought to that state in which they can be spun into threads. As the quantity and quality of the product depend much on this preliminary operation, it becomes of the greatest consequence that it be properly conducted. During this process carbonic acid and hydrogen gas are given out. The extrication of these gases is owing to a glutinous juice, which holds the green colouring part of the plant in solution, and which is the medium of union between its cortical and ligneous parts, undergoing a certain degree of putrefaction. This substance seems to resemble the glutinous part, which is held dissolved in the juice obtained from plants by pressure; is separated from the colouring particles by means of heat; readily becomes putrid; and by distillation affords ammonia. But although it is held in solution with the expressed juice, it would appear that it cannot be separated from the cortical parts completely by means of water; and hence it happens that hemp or flax watered in too strong a current has not the requisite softness and flexibility. But, on the other hand, if the water employed in this operation be stagnant and in a putrid state, the hemp or flax becomes of a brown colour, and loses its firmness. In the one case the putrefactive process is interrupted; in the other it is continued too long and carried too far. This process, therefore, is performed with the greatest advantage in places near the banks of rivers, where the water may be changed so frequently as to prevent such a degree of putrefaction as would be injurious to the flax, as well as prejudicial to the workmen, from noxious exhalations; and at the same time not so frequently as to retard or interrupt those changes which are necessary for rendering the glutinous substance soluble in water.

By the process of watering flax, and by drying before and after that process, the green-coloured particles undergo a similar change to that which is observed in the green substance of the plants exposed to the action of air and light. The next part of the process, therefore, after watering, is to spread it out upon the grass, and thus expose it for some time to the air and sun. By this means the colour of the lint is improved, and the ligneous part becomes so brittle that it is easily separated from the fibrous part. This operation, as is well known, is usually performed by machinery.

The fibres of lint possess no perceptible degree of elasticity, and they appear to be perfectly smooth. No roughness or inequality can be detected by the feel, and no imperfections can be perceived, even with the assistance of the microscope. Experience shows, that it produces no irritation on wounds or sores which are dressed with it, as is known to happen from a similar application of cotton stuffs.

Flax which is intended for dyeing must be subjected to a similar series of operations with cotton, in the different processes of scouring, aluming, and galling. A repetition of the mode of performing these operations is therefore unnecessary.

**CHAPTER III.**

**OF MORDANTS.**

The term mordant is applied by dyers to certain substances with which the cloth to be dyed must be impregnated, otherwise the colouring matters would not adhere to the cloth, but would be removed by washing. Thus the red colour given to cotton by madder would not be fixed, unless the cloth were previously steeped in a solution of a salt of alumina. It has been ascertained that the cloth has the property of decomposing the salt of alumina, and of combining with and retaining a portion of alumina. The red colouring principle of the madder has an affinity for this alumina, and combines with it. The consequence is, that the alumina being firmly retained by the cloth, and the colouring matter by the alumina, the dye becomes fast, or cannot be removed by washing the cloth with water, even by the assistance of soap, though simple water is sufficient to remove the red colouring matter from the cloth, unless the alum mordant has been previously applied.

The term mordant (from the Latin word *mordere*, to bite) was applied to these substances by the French writers on dyeing, from a notion entertained by them that the action of the mordants was mechanical; that they were of a corrosive or biting nature, and served merely to open pores in the fibres of the cloth, into which the colouring matter might insinuate itself. And after the inaccuracy of this notion was discovered, and the real use of mordants ascertained, the term was still continued, as sufficiently appropriate, or rather as a proper name, without any allusion to its original signification.

The term mordant, however, is not limited to those substances merely which serve, like alumina, to fix the colours. It is applied also to certain substances, which have the property of altering the shade of colour, or of brightening the colour, as it is called. Thus *cream of tartar* is usually called a mordant, because when chloride of tin is used, as is the case in the red dye upon silk or woollen, the addition of cream of tartar is necessary, not merely to brighten the colour, but to cause its equable application upon the cloth; for when the tartar is omitted, we observe that the shade is very unequal upon different parts of the surface, some spots being much darker and some much lighter than others. We believe that tartar acts chiefly, if not entirely, by forming a double salt with the chloride of tin, from which the tin is not liable to be partially precipitated. The consequence of this is, the equal distribution of the tin through the whole liquid, and the consequent equality of its application on the cloth. For the The mordants employed by dyers are but few in number. Alumina, the oxides of tin, the protoxide of lead, the black oxide of copper, and the infusion of nutgalls constitute almost the whole of them. The peroxide of iron and the sesquioxide of manganese have also a strong affinity for cloth, especially for cotton cloth, and are frequently employed; but they serve at once the purpose of mordants and colouring matters. We believe also that in one important process for giving a fine red to cotton, what is usually called the Turkey-red dye, the margarate of potash constitutes an indispensable mordant.

Let us take a view of these different mordants in succession.

1. **Alumina**—This is a soft, white, tasteless powder, insoluble in water, but soluble in acids, and constituting sweet-tasted and astringent salts, which have the property of reddening vegetable blues. These salts are soluble in water, but very few of them are capable of crystallizing. Of all the salts of alumina, the most important is alum, the nature and properties of which have been described in another part of this work. See **Alum**.

It is a double salt, composed of three integrant particles of sulphate of alumina united to one integrant particle of sulphate of potash or sulphate of ammonia and twenty-five integrant particles of water. The ammoniacal alum is less soluble in cold water than the potash alum; but both kinds are sufficiently soluble in hot water. Such is the affinity of alumina for woollen or silk stuffs, that when they are plunged into a solution of alum, the alumina leaves the sulphuric acid with which it was united, and combines with the fibres of the cloth. The affinity of alumina for cotton or linen, though considerable, is not so great as its affinity for wool or silk. On that account the cotton dyers and calico printers find it requisite to combine the alumina, before using it as a mordant, with a weaker acid than the sulphuric. The acetic is the one which has been made choice of, and the acetate of alumina is prepared by the following process: Three parts of alum and one part of acetate of lead are dissolved in eight parts of hot water. There is then added one-eighth of a part of potash and as much chalk. The reason of the addition of the potash and the chalk is, that one part of acetate of lead is not sufficient to decompose three parts of alum. These substances prevent the residual alum from crystallizing, by decomposing it. The proper quantities of these salts which the dyers ought to employ are six parts of alum and seven parts of sugar of lead. These proportions would just convert the sulphate of alumina of the alum into acetate of alumina, without altering the sulphate of potash.

The wool or silk is put into a hot solution of alum, and the cotton into a hot solution of acetate of alumina, and passed through the liquid till a sufficient quantity of the alumina has combined with the fibres of the cloth. It is then wrung out, washed, and dried. The alumina remains firmly adhering to the cloth, and cannot be removed by washing, bleaching, or any of the processes to which such cloths are usually subjected.

In order to form some notion of the quantity of alumina fixed upon cloth by the alumining process, the writer of this article made the following experiments: A quantity of cotton cloth was procured, such as is sometimes used for making light dresses of Turkey red. Of this, 1000 grains were burnt, and the ashes being reserved and analyzed, were found to contain 0.4 grain of alumina. 1000 grains of the same cloth which had been dyed Turkey red, and of course subjected to the alumining process, were burnt, and the ashes subjected to a chemical analysis. The alumina contained in them weighed eight grains. Hence 7.6 grains of this matter had combined with the cloth in the process of alumining.

The length of 1000 grains of the undyed cotton cloth was one yard five and two-third inches, and its breadth thirty-three inches. The length of 1000 grains of the Turkey red cloth was one yard and six inches, with a breadth of thirty-three inches. The two pieces of cloth, therefore, were very nearly of a size. We see that the dyed cloth had been stretched a very little during the processes to which it had been subjected. Thus it appears that a surface of cloth amounting to 1386 square inches, or rather 2772 square inches (as both sides of the cloth had been equally subjected to the alumining process), had combined with 7.6 grains of alumina, or every square inch of the cloth had combined with 0.0027 grains (or 1/37th grain nearly) of alumina. Small as this quantity may appear, it was sufficient to fix the red colouring principle of madder, and to constitute a very deep and beautiful dye.

A very pale shade of red is sometimes given to a portion of the cloth, which has a beautiful effect when contrasted with the deep Turkey-red dye. This is produced by limiting the quantity of alumina applied to the parts which are to be light red. In fact, no alum mordant whatever is applied to the parts which are to be light red; but they get a little during the steps taken to remove the excess of aluminous mordant, which has been applied to the parts that are to get the deep-red colour.

To ascertain the quantity of alumina which was sufficient to fix the light-red colour, the writer of this article got a portion of the same cotton cloth formerly operated on, dyed of the light-red colour. 1000 grains of this cloth being burnt, and the ashes analyzed, were found to contain 0.4 grain of alumina. Subtracting the 0.4 grain of alumina which 1000 grains of the undyed cloth contained, there remains 0.4 grain for the quantity communicated during the alumining process. These 1000 grains of cloth constituted a length of one yard and ten two-third inches. The breadth was thirty-two inches. Its surface (reckoning both sides) constituted 2986½ square inches. So that every square inch of surface had combined with 0.00012 grains of alumina, or less than 1/8000th of a grain. Yet this quantity of alumina, small as it is, was essential to the permanence of the dye; for when unalumined cloth was dyed with madder, the colour was speedily and easily washed out by water; but the light-red Turkey-red dye was perfectly fixed.

These facts are sufficient to show us the very small size of a particle of alumina. Were only 1000 particles of this substance fixed upon the square inch of surface of cloth, the weight of a particle of alumina would not exceed the millionth part of a grain. But that the number far exceeds 1000 is evident from this, that when we examine the surface of the cloth with a microscope, the red colour does not appear in spots, but is equally spread over the whole cloth. Many thousand particles of alumina upon the square inch would be requisite to produce this effect.

The alumining and the dyeing are sometimes given to the cloth together; but more frequently the alumining precedes, and the dyeing follows after the cloth has imbibed the mordant and been washed and dried.

2. **Tin**—Of all the metallic oxides, those of tin are the most useful as mordants. They form, with acids, salts very easily decomposed; and the fibres of cloth have an affinity so strong for these oxides, that they readily withdraw them from their saline combinations, and unite with them. Tin forms two different oxides with oxygen. The protioxide is black, but the peroxide is yellow, and sometimes also white. Mordants. The tin mordants are formed by dissolving tin in muriatic acid. There are two chlorides of tin, as the combinations of that metal with chlorine are called. These are, the protocloride and the perchloride. The protocloride, when anhydrous, is a gray solid, with a pearly lustre; but when it is formed by dissolving tin in muriatic acid, it crystallizes in large oblique four-sided prisms, with one edge usually replaced by a tangent plane. The colour is white, with somewhat of the diamond lustre. The taste is acid, acrid, and disagreeable. When recently formed they dissolve in water; but when kept they dissolve imperfectly, leaving a white matter behind, which is an oxide of tin, and the quantity of this insoluble oxide increases with the age of the crystals.

Calico-printers form their tin mordant by dissolving tin directly in muriatic acid; but the silk and woollen cloth dyers employ aqua regia for the purpose. Indeed tin for the dyers was originally dissolved in weak nitric acid; but when this method is followed, almost the whole tin precipitates in the state of an oxide in a few days. To prevent this precipitation, they added a little common salt or sal ammoniac to the nitric acid in which the tin was to be dissolved. Hellot informs us that Baron claimed the merit of having been the first person who employed aqua regia at Carcassone to dissolve tin. The object in view was to prevent the precipitation of the oxide, which always happens when nitric acid alone is used for that purpose.

The dyer's ordinary solution of tin is made with the kind of nitric acid called single aqua fortis. It is capable of dissolving about the eighth part of its weight of granulated tin. For each pound of aqua fortis it is usual to add about two ounces of common salt or sal ammoniac, and a little water to moderate the action of the acid. Those solutions which have been made most slowly, and with the least separation of fumes or vapours, have been found to succeed best; showing clearly that it is the protocloride of tin that constitutes the proper mordant. Two ounces of grain tin are usually allotted to every pound of aqua fortis. The metal should be added at different times, waiting till one part is nearly dissolved before another is added, otherwise too much heat may be evolved, which would cause the solution to go on too rapidly. The quantity of water added should be about one half of that of the aqua fortis used; so that the solution, when completed, should contain about one thirteenth of its weight of tin. About 20 lbs. of such a solution is required to die 100 lbs. of woollen cloth a full cochineal scarlet.

The process usually followed is this: Supposing 100 pounds weight of cloths intended to be died; ten pounds of cream of tartar are put into a suitable dyeing vessel of pure block tin, with a sufficient quantity of clean soft water, and six or eight ounces of powdered cochineal. Immediately after this, ten or twelve pounds of the solution of tin are to be added, and when the mixture is nearly boiling hot, the cloth, previously completely wet, is put into the dyeing liquor, and turned through it by the winch, at first very rapidly, and afterwards slowly. This is to be continued for an hour and a half, after which the cloth is to be taken out and rinsed in clean water. By this first process the cloth has acquired a flesh colour. For the second or dying process the tin vessel is replenished with clean water. Five or six pounds of cochineal in powder are to be put into it, and well mixed by stirring it for a few minutes. After this the remaining part of the solution of tin is to be added; and the whole being well stirred, the cloth is to be put into the liquor, and turned very briskly through it, until both ends may receive an equal portion of the dye. After this it is turned more slowly for the space of half an hour, or until the dyeing liquor becomes exhausted, when the cloth is to be taken out, aired, and rinsed.

The process followed by the calico-printers for preparing the tin mordant is to dissolve tin in muriatic acid, by which a protocloride of tin is obtained. But Dr Bancroft found that, when a saturated solution of tin in muriatic acid was employed for dyeing woollen cloth scarlet, it had a corrosive effect on the cloth. He recommends a mixture of nitric and muriatic acid as a good solvent; and doubtless such a mixture would be cheaper and better than a solution of common salt or sal-ammoniac in nitric acid. Dr Bancroft found that a mixture of sulphuric and muriatic acid made a good solvent for the tin. Some farther experiments are still wanting to elucidate the best state of the tin mordant for the scarlet dye. We are of opinion that it is the protocloride of tin that constitutes the true mordant; but some addition seems necessary to enable the fibres of the cloth to separate the oxide of the tin from the combination in which it exists, or rather to unite with the muriatic acid, when it is formed and disengaged by the decomposition of water, which obviously takes place; otherwise this acid, when evolved, will exert a corrosive action on the cloth.

The tartar is necessary to produce the scarlet colour. Without it the colour of the cochineal dye is crimson, or at most a rose colour. It doubtless acts principally by forming a double salt with the chloride of tin. But it must also convert a portion of the cochineal into a yellow dye; for scarlet is a compound colour, consisting of a great deal of red, mixed with a small quantity of yellow.

3. Lead.—We are not aware of the protoxide of lead being employed in any case as a mordant in dyeing silks or woollen cloth; but of late years it has been used as a mordant for cotton, to which the beautiful yellow given by means of chromic acid was to be communicated. For this purpose the lead is dissolved in nitric acid, or converted into nitrate of lead. This salt crystallizes in octahedrons, has a sweet and astringent taste, and dissolves readily in water. An aqueous solution of it thickened by gum is applied to those parts of the cloth which are to receive a yellow colour; or if the cloth has been already dyed red, a quantity of tartaric acid is mixed with the solution of nitrate of lead and gum, and after it has been applied and dried on the cloth, the piece is passed through water impregnated with a quantity of bleaching powder. The red colour is discharged; but the oxide of lead, which had united with the fibres of the cloth, still continues to adhere without alteration. The cloth is now passed through a solution of bichromate of potash. Those parts of it which contained the oxide of lead immediately decompose the bichromate; chromate of lead is formed and fixed upon the cloth, constituting a most beautiful and indelible yellow colour; or, by particular alterations in the process, this yellow colour may be changed to red, or to a very deep orange approaching red, and exceedingly beautiful.

4. Copper.—The black oxide of copper is employed as a mordant in giving a black colour to hats, or at least acetate of copper is employed in the process; and it is not easy to conceive any other purpose which such a salt can serve than Nutgalls are excrescences which grow on The branches of some species of oak, in consequence of the puncture of an insect, the *cynips quercus folii*. The best kind come from the Levant. They are nearly spherical bodies, with protuberances on the surface. There is a cavity within where the insect lodged, and a round hole from that central cavity to the surface, by which the insect, after it was hatched from the deposited egg, eat its way out. These nutgalls have a very astringent and austere taste. When digested in water they give that liquid a brown colour, and the taste which they themselves have. When such an infusion is mixed with a solution of sulphate of iron, it strikes a deep blue or black colour. Nutgalls, besides a considerable portion of woody fibre, contain a notable quantity of two peculiar vegetable substances, to which they owe their value as dyestuffs or mordants. These are *tannin* and *gallic acid*. The latter of these substances is easily obtained in a state of purity; the former with difficulty.

The infusion of nutgalls contains scarcely any thing else than a solution of tannin and gallic acid. If we evaporate the solution in a gentle heat to dryness, and digest the residue in sulphuric ether or absolute alcohol, the gallic acid will be dissolved, and the tannin will remain in a state of tolerable purity, only coloured brown by the action of the air. Tannin, when pure, is white while moist. It becomes yellow when dried even in vacuo, and by subsequent exposure to the air it becomes darker coloured. Its taste is excessively astringent and harsh; and it is distinguished by the property of striking a deep blue or black with the salts of iron. Tannin is easily altered in its nature by heat. Its constitution, as determined by the experiments of Berzelius, is as follows:

\[ \begin{align*} \text{Carbon} & : 52-09 \text{ to } 52-49 \\ \text{Hydrogen} & : 3-86 \text{ to } 3-79 \\ \text{Oxygen} & : 43-45 \text{ to } 43-72 \\ \end{align*} \]

This corresponds best with

\[ \begin{align*} 7 \text{ atoms carbon} & : 5-25 \\ 3 \text{ atoms hydrogen} & : 0-375 \\ 4 \frac{1}{3} \text{ atoms oxygen} & : 4-333 \\ \end{align*} \]

Hence it is either composed of these atoms or of some multiple of them, most probably of

\[ \begin{align*} 21 \text{ atoms carbon} & : 15-75 \\ 9 \text{ atoms hydrogen} & : 1-125 \\ 13 \text{ atoms oxygen} & : 13-00 \\ \end{align*} \]

This would make its atomic weight 29-875.

Tannin exists not merely in nutgalls, but in oak bark, in the wood of the oak, in the leaves, and in fact in every part of that tree; but the quantity of it is much greater in nutgalls than in any other part.

Tannin possesses the characters of an acid. It reddens vegetable blues, effervesces with the carbonates, and unites in definite proportions with the bases.

*Gallic acid* exists also as a constituent of nutgalls, and may be extracted from them by means of ether or absolute alcohol. Its colour is white, though it is apt, like tannin, to become yellow when exposed to the atmosphere, and seems indeed capable of being converted into tannin by exposure to too high a temperature. It is not nearly so soluble in water as tannin, and is distinguished by an acid taste instead of an astringent one. Like tannin, it strikes a black with the salts of iron. But the gallate of iron is readily distinguished from the tannate. The former is an exceedingly fine black powder, which precipitates very slowly, while the latter is a deep blue, which precipitates rapidly, has a coarse appearance, and becomes Mordants black when dry. The constituents of gallic acid, according to the analysis of Berzelius, are as follows:

\[ \begin{align*} \text{Carbon} & : 56-64 \\ \text{Hydrogen} & : 5-00 \\ \text{Oxygen} & : 38-36 \\ \end{align*} \]

This corresponds with

\[ \begin{align*} 7 \frac{1}{2} \text{ atoms carbon} & : 5-625 \\ 4 \text{ atoms hydrogen} & : 0-5 \\ 4 \text{ atoms oxygen} & : 4-0 \\ \end{align*} \]

Or, if we double the quantities to get rid of the half atom,

\[ \begin{align*} 15 \text{ atoms carbon} & : 11-25 \\ 8 \text{ atoms hydrogen} & : 1-00 \\ 8 \text{ atoms oxygen} & : 8-00 \\ \end{align*} \]

In gallic acid the hydrogen and oxygen exist in the proportions which constitute water; but in tannin there is a surplus of oxygen. In gallic acid there is rather more hydrogen than in tannin.

The great use to which the infusion of nutgalls is put How used in dyeing is to give a black colour when mixed with solution of sulphate of iron. When used in this way it perhaps is improperly named a mordant; for the oxide of iron is known to have a strong affinity for the fibres of cloth, and the tannin and gallic acid have a strong affinity for the oxide. Hence probably the way in which the black dye is fixed on silk and woollen cloth. There can be no doubt that the tannin, which is by far the most abundant ingredient, is the principal agent in striking the black with the sulphate of iron. But the gallic acid probably adds to the lustre, and improves the beauty of the colour.

In the Turkey-red process for giving a fixed red colour to cotton cloth by means of madder, steeping the cloth in infusion of nutgalls is an important part of the process, as without this the colour would be apt to want equality of shade in different parts of the cloth. In this process there can be no doubt that tannin acts the part of a mordant. The galling, in preparing the cloth for the Turkey-red dye, always precedes the alumina process. Whether it has the property of making the alumina more fixed on the cloth than it otherwise would be, or what other purpose it may serve, is not very well understood; but it is certain that the boiling of the cloth in a pretty strong infusion of galls is important. The infusion of galls is made by boiling twenty-five pounds of nutgalls in forty gallons of water, till four or five gallons are boiled or evaporated. The specific gravity of the infusion is 1-020; or sometimes the process is twice repeated, employing each time only twelve and a half pounds of nutgalls in forty gallons of water. The specific gravity of each infusion in that case is only 1-010.

Such is an account of the mordants at present employed in dyeing, and the way of using them. It is not always necessary to employ mordants in dyeing; some colouring matters adhere to the cloth without the presence of any intermediate substance. This is the case with the oxides of iron and manganese. It is the case also with indigo, and it was the case also with the colouring matter from the buccinum and purpura employed by the ancient Phoenician dyers in dyeing the celebrated purple, of which an account has been given in the first chapter of this treatise.

To those colouring matters which adhere to the cloth of themselves Bancroft has given the name of substantive colours, while he distinguishes those that require a mordant by the name of adjective colours. Mordants have a very considerable effect on the colour; and by varying the mordant, very different colours, and a great variety of shades, may be obtained from the same colouring matter. Some mordants themselves may be considered as communicating a colour, without the addition of any colouring substance; and although, when the latter is added, a new set of affinities is brought into action, yet there is little doubt that the mordant also has a considerable share in fixing the shades of colour. Let us take an example in dyeing with cochineal. When the alumious mordant is employed, the colour produced is crimson; but when the oxide of iron is substituted for the alumina, the colour obtained is black. The effect is obviously produced by a change in the action of the affinities between the colouring matter and the mordant, and the colouring matter and light. In the use of mordants, therefore, it is necessary to attend to their combined effects with the colouring matter employed, and, to be able to communicate particular colours to stuffs with any degree of certainty, to know the amount of that effect.

Even in the mode of applying mordants, the variety of shades may be greatly multiplied. Different effects, for instance, are produced by previously impregnating the stuff with the mordant, or by mixing it with the bath. Different effects also arise from using heat, or as the stuff is more or less rapidly dried; and this must appear to be the case, if we consider the different affinities which are in action, and the change on the action of these affinities in these different circumstances, as well as in others which can scarcely be appreciated. The combination of these substances which have an affinity for the stuff, and the decompositions which are the result of that combination, are greatly facilitated by the evaporation of the water or other liquid which held these substances in solution; because by its affinity, which is opposed to the action of the affinity between these substances and the stuff, the affinity of the latter produces a more limited effect. But in dyeing, the process should proceed slowly, that the substances may not be separated before their mutual affinities have begun to operate.

Considerable differences must be observed in the mode of employing the mordant, as the force of affinity between the stuff and the colouring matter is greater or less. When this affinity is strong, the mordant and the colouring substance may be mixed together; the compound thus formed immediately enters into combination with the stuff. But if the affinity between the stuff and the colouring particles be weak, the compound formed of the latter and the mordant may separate, and a precipitation take place, before it can be attached to the stuff; and hence it is in these cases that the mordant, which is to serve as the medium of union between the stuff and the colouring matter, must be combined with the former, before the application of the latter. It is from these differences that different processes must be followed in fixing colouring matters on animal and vegetable productions; as, for instance, in dyeing wool or silk black, or with cochineal.

In estimating the effects of mordants, and in judging of the most advantageous manner of applying them, it is necessary to attend to the combinations which may be formed, either by the action of the ingredients of which they are composed, or by that of the colouring matter and the stuff. It is necessary also to take into consideration the circumstances which may tend to bring about these combinations with more or less rapidity, or that may render them more or less perfect. The action which the liquor in which the stuff is immersed may have, either on its colour or texture, must also be considered; and, to be able accurately to judge of the extent of this action, we must know the proportions of the principles of which the mordant is composed; which of these principles remains in an uncombined state in the liquor; and the proportion or quantity which is thus separated.

CHAPTER IV.

OF THE MODE OF DYEING SIMPLE COLOURS.

Dyers have divided colours into two classes, namely, simple and compound colours. The simple are produced by a single dyeing process, and cannot be obtained by mixing together different colours. The compound colours are obtained by mixing together any two of the dyestuffs which produce the simple colours. By this means two colours are given to the cloth at once; and the shade depends upon the proportions of each dyestuff employed.

The simple colours are five in number; namely, red, yellow, blue, black, and brown. The last of these may be considered also as a compound colour, as it may be formed by mixing the dyestuffs for two simple colours together. The compound colours are orange, green, purple, and grey. We shall in this chapter confine ourselves to the mode of dyeing the simple colours, dividing it into five sections, in each of which we shall treat of a simple colour.

Sect. I.—Of Red.

In treating of the red dye, the simplest method seems to be to give an account, in the first place, of the dyestuffs employed for dyeing red; and in the second place, to describe the methods followed by the dyer to give a red colour to silk, wool, cotton, and flax.

I.—Description of the Dyestuffs.

The principal colouring matters used in dyeing red are madder, cochineal, kermes, lac, archil, carthamus, Brazilwood, and logwood.

1. Madder is the root of a plant, the rubia tinctorum, which is cultivated in the south of Europe. There are two varieties, the rubia cordifolia and the rubia peregrina. It is this last which is cultivated in the south of Europe, and comes to us from the Levant. The roots are wiry, and very much branched. They have a red colour externally, but are yellow within. This plant was cultivated by the Greeks and Romans, and was employed in medicine, and also in dyeing, as Dioscorides and Pliny inform us. It was called erythrodamus and verrucaria by the Greeks, and rubia by the Romans. From the last Greek name is derived the French word garance, by which madder is distinguished in that language.

It is the woody portion of madder that is useful in dyeing; the bark and pith are comparatively of little value. Madder has been examined by many chemists; but Robiquet and Colin alone have succeeded in separating the red colouring matter, and in determining its properties. They have distinguished it by the name of alizarin, an appellation derived from alizar, by which madder is distinguished in the Levant.

Madder contains two colouring matters; one, which is yellow, is soluble in cold water; the other, the alizarin, is soluble only in boiling water. To the yellow colouring matter Kuhlmann has given the name of xanthin. This matter considerably injures the colour of the alizarin; hence the reason why cloth dyed with madder has at first a dull brownish-red colour, which it loses in proportion as the xanthin is removed.

To obtain alizarin, Robiquet and Colin recommend the following process. Mix pounded madder with two thirds or with its own weight of concentrated sulphuric acid, and set the mixture aside for two or three days, taking care that heat is not evolved. All the other constituents of the madder, except the alizarin, are converted into charcoal; and should heat have been evolved, even the alizarin itself will be charred. Wash the black matter thus formed, to extract from it all the acid. What remains is a mixture of charcoal and alizarin. Let it be dried and digested with a portion of cold alcohol, which will dissolve a fatty matter which it contains. Let it now be digested in boiling alcohol till all the alizarin is dissolved. Mix the alcoholic solutions with water, distil off the alcohol, and filter the residual liquor. The alizarin remains upon the filter in a state of purity. Various other processes for extracting alizarin have been given by Robiquet and Colin, and by Kuhlmann and Zenneck. But for these we refer to the respective publications of these chemists. The process which we have given we consider as of easiest execution.

Alizarin is insipid, and destitute of smell. According to Zenneck, it possesses weakly acid properties; but Colin and Robiquet consider it as perfectly neutral. It sublimes easily in long flexible capillary needles, having an orange colour; but unless the subliming vessels be very low and flat, much of the alizarin is decomposed during the process. Two watch-glasses applied to each other, for example, answer very well as a subliming vessel. During the process the alizarin gives out an aromatic odour like that of benzoin. It is almost insoluble in cold water; but it is moderately soluble in boiling water, to which it communicates a rose-red colour. At the temperature of 54°, 212 parts of alcohol, of the specific gravity 0·83, dissolve one part of alizarin. At the same temperature sulphuric ether, of specific gravity 0·73, dissolves 1/10th part of its weight of it. The alcoholic solution is red, that of ether yellow or orange. It is slightly soluble in bisulphide of carbon, oil of turpentine, naphtha, and the fat oils, communicating to these bodies a reddish-yellow colour. Chlorine has little action on it, yet it injures the colour a little, and makes it incline to yellow. Sulphuric acid dissolves it, and acquires at the same time a blood-red colour. Nitric and muriatic acid dissolve it, and slightly alter the shade of its colour. These acids, when dilute, do not dissolve it. With alkalies it forms soluble combinations, having a violet-red colour, which do not afford crystals. The alkaline carbonates dissolve it, assuming a violet colour. With the alkaline earths it forms precipitates, having a violet or lilac colour; with alumina a precipitate which is red or reddish-brown. With the metallic oxides it forms insoluble combinations, having a violet or reddish-brown colour.

It has a marked affinity for various animal matters. It dissolves in the white of an egg diluted with water; and if we coagulate the albumen by heat, the alizarin combines with it, leaving the liquid portion tinged yellow. Albumen, containing a portion of alizarin in solution, is precipitated by a solution of chloride of calcium; yet this salt does not precipitate uncombined albumen diluted with the same quantity of water. Phosphate of lime appears also to have a marked affinity for the colouring matter of madder. Indeed this is obvious, from the well-known fact, that the bones of animals which have taken for some time a quantity of madder mixed with their food, are tinged red.

Urine, when left in contact with madder, extracts from it the alizarin, and acquires a red colour, even when quite recent and acid. Milk is coloured yellow by madder, and red coagulated curd is deposited upon the madder. The solution of animal gelatin does not precipitate the red colouring matter of madder.

We are not aware that madder is employed in dyeing silk or wool, but it constitutes one of the most beautiful and fixed red dyes for cotton and linen, and for dyeing these substances it has been in use probably at least two thousand years. As the yellow colouring matter or zemthin is not used in dyeing, it seems unnecessary to give any account of it in this place. It gives a very beautiful yellow colour, and might be employed in calico-printing, were it not that the extraction of it would cost too much money.

2. Cochineal is the name given to a small insect that inhabits the cactus coccinellifera, and three or four other species of cactus, upon which it remains immoveable, drawing its nourishment from the juices of the plant. The insect is called by entomologists coccus cacti. It is the female insect (which is without wings) that constitutes the dyestuff. The insect is small, having a kind of hemispherical back, crossed by numerous wrinkles, and of a dark reddish-brown colour.

This insect is a native of Mexico, and had been employed by the natives as a red tinging matter. When the Spaniards entered that country in 1518 it drew their attention; and in 1523 Cortes received orders from the court of Spain to procure it in as great quantity as possible. He left the cultivation of the insect to the natives, who prosecuted it so successfully that great quantities of it were imported into Europe. The earlier Spanish writers described it as an insect, but at a later period it came to be considered as the seed of a plant; and this opinion continued the prevalent one, till the contrary was proved by Melchior de Ruuscher, about the beginning of the eighteenth century. This man, who was a native of Holland, affirmed in a society, from oral information which he had obtained in Spain, that cochineal was a small animal. Another person, whose name has not been made known, maintained the contrary with so much heat and violence, that the dispute at length ended in a bet. Ruuscher charged a Spaniard, one of his friends, who was going to Mexico, to procure for him in that country authentic proofs of what he had asserted. These proofs, legally confirmed in October 1725, by the court of justice in the city of Antigua, in the valley of Oaxaca, arrived at Amsterdam in the autumn of the year 1726. Ruuscher caused this evidence to be published under the following title: The History of Cochineal proved by authentic documents.

The fact that cochineal is an insect had been suspected before. In a very crude and unsatisfactory paper on cochineal, published in the Philosophical Transactions for 1668, this is distinctly stated as an undoubted fact. In 1672 Dr Lister, in a paper inserted also in the Transactions, throws out a conjecture that the cochineal insect may be a sort of kermes; which conjecture is now known to be well founded. Leeuwenhoek is said to have examined cochineal microscopically in 1703, and to have ascertained it to be an insect. About the beginning of the year 1757 Mr Ellis obtained some of the joints of the plant on which the

---

1 See Kuhlmann, Ann. de Chim. et de Phys. xxiv. 225; Zenneck Poggendorf's Annalen. xiii. 261; Robiquet et Colin. Jour. de Pharmacie, xii. 497; and Ann. de Chim. et de Phys. xxxiv. 225. 2 For an account of it we refer the reader to the Jour. de Pharmacie, xlv. 354. 3 Naturaalgie Historie van de Couchenille, bewezen mit authentique documenten. Amsterdam, 1729, 8vo, 175 pages. 4 No. xl. p. 796. Simple insects breed, from South Carolina, and presented them the same year to the Royal Society. These specimens, Mr Ellis observes, were full of the nests of this insect, in which it appeared in its various states, in the most minute, when it walks about, to the state when it becomes fixed, and wrapt up in a fine web which it spins about itself. With the assistance of the microscope, Mr Ellis discovered the true male insect in the parcels which had been sent to him from America; and in August 1756, in consequence of Mr Ellis's discovery, Dr Garden caught a male cochineal fly, which, he observes, is rarely to be met with. He supposes that there may be 150 or 200 females for one male. These discoveries proved indisputably that the cochineal is an animal production.

Cochineal has been subjected to a chemical examination by various individuals; but the most successful analysis of it is by Pelletier and Caventou in 1818, which was published in the eighth volume of the Annales de Chimie et de Physique, p. 250. They found it to contain about half its weight of the peculiar colouring matter to which they applied the name carmine; but we prefer the name cochinealin, already given to this substance by John, who was the person that first obtained it and described its properties. Cochinealin may be obtained by the following process:

Digest cochineal in alcohol, as long as it communicates a red colour to that liquid. The alcoholic solution being left to spontaneous evaporation, lets fall a crystalline matter of a fine red colour. Dissolve these crystals in strong alcohol, and mix the solution with its own bulk of sulphuric ether. The liquid becomes muddy, and gradually deposits the cochinealin, which constitutes a purple crust on the bottom of the vessel.

Cochinealin has a fine purple-red colour, is granular, and consists of small crystals. When left exposed to the air, it undergoes no sensible alteration. At 122 degrees it melts; and if the heat be increased, it swells up and is decomposed, yielding carburetted hydrogen gas, a great deal of oil, and a little water having a slightly acid taste. It furnishes no traces of ammonia.

It is very soluble in water. The aqueous solution has a fine carmine colour, and, how much soever concentrated, does not deposit crystals. It dissolves also in alcohol; but the solubility diminishes in proportion to the strength of the alcohol. In sulphuric ether it does not dissolve. The weak acids dissolve it, probably in consequence of the water which they contain. When the cochinealin is pure, no acid throws it down from its aqueous solution; but they precipitate it when in combination with the peculiar animal matter of cochineal. They produce a sensible change upon its colour, causing it gradually to assume a tint of yellow. This is the reason why cochineal will not dye scarlet, unless when mixed with bitartrate of potash. The concentrated acids decompose it altogether.

Alkalies also alter the colour of solutions of cochinealin. It first becomes violet, and at last yellow; and the original colour cannot be again restored. Lime-water occasions a precipitate when poured into an aqueous solution of this substance; but barytes and strontian water occasion no precipitate, though they change the colour to yellow. Alumina has a strong affinity for cochinealin. When newly precipitated alumina is agitated in an aqueous solution of it, the liquid is rendered colourless, and the alumina converted into a beautiful lake. The pigment called carmine, accidentally discovered by a Franciscan monk about the middle of the sixteenth century, and the process for obtaining which was published by Homberg in 1656, consists essentially of a combination of cochinealin and alumina.

Most of the saline solutions alter the colour of the aqueous solution of this substance; but few of them are capable of producing a precipitate in it. Acetate of lead, however, throws down a copious violet sediment from the decoction or infusion of cochineal; and by decomposing this sediment by means of sulphuretted hydrogen, the cochinealin may be obtained in a state of purity. The chloride of tin throws down a violet precipitate, and the perchloride strikes a fine scarlet colour, but precipitates nothing. When gelatinous alumina is added to this mixture, we obtain a fine red precipitate, which is not altered by boiling.

Cochineal was at one time used in great quantity in Europe, chiefly for dyeing fine scarlet cloth. When Bancroft published his work on colours in 1794, he informs us that the annual European consumption was about 3000 bags, or 600,000 lbs., of which about 240,000 lbs. were consumed in Great Britain. The demand has since that time very much diminished; and the price has in consequence sunk from about thirty shillings to about nine shillings and sixpence per pound. This diminution is chiefly owing to the substitution of the lac dye for cochineal. Cochineal, however, is still used for the dyeing of fine scarlet cloth.

3. Kermes.—This is also the female of an insect which inhabits a species of oak. The tree, which is a native of the countries bordering on the Mediterranean and Asia, is called by Linnaeus quercus ilicis, and the insect coecus ilicis. This substance was known to the ancients, though they were ignorant of its nature. Dioscorides calls it kockos, and Pliny coecum and gramum. It was used in medicine; and there can be no doubt that it was employed in Asia at a very early period as a dyestuff. There is reason to suspect that the scarlet cloth mentioned by Moses to adorn the tabernacle was dyed by means of kermes. If this conjecture has any foundation, the kermes dye must have been known in Egypt before the time of Moses.

The word kermes or alkernes is at present in the East the common name for the animal which produces the dye, as well as for the dye itself. Probably it comes from the Arabic. If the kermes dye was known in Egypt and Phoenicia in the time of Moses, there is some difficulty in explaining how it was altogether unknown to the Greeks and Romans till the time of the Emperor Aurelian, who began his short reign in the year 270 of the Christian era. Vopiscus informs us that the king of Persia sent to that emperor, besides other articles of great value, some woollen cloth, which was of a much costlier and brighter purple than any that had been ever seen in the Roman empire, and in comparison of which all the other purple worn by the emperor and the ladies of the court appeared dull and faded. Vopiscus goes on to say that this cloth had been dyed in India, and that the assertion of the king of Persia, sune purpuram qualis apud nos est, was false; for Aurelian, Probus, and Diocletian, had sent dyers into the East on purpose to get information respecting this precious dye; but that their attempts utterly failed of success.

From this passage it would appear that the use of kermes in dyeing had been known at a very early period in India, from which it gradually made its way into Persia, and afterwards into Europe. And as the colour which it yielded was more beautiful than the celebrated Phoenician dye, it may have contributed to put an end to the monopoly of the Phoenician dyers. The term scarlet, the origin of which is unknown, but which was certainly employed early in the twelfth century, was applied to the colour given to cloth by the kermes dye.

Kermes is gathered chiefly in Languedoc, Spain, and Portugal. The insects are collected in the months of May and June, when the female, which alone is useful, is distended with eggs. To destroy the young insects, the kermes is exposed to the steam of vinegar for about half an hour, and afterwards dried. It is in the form of small grains of a reddish-brown colour. Kermes, as appears from the experiments of Lassaigne, contains the very same colouring matter as cochineal; but its quantity is not so great, and of course it is mixed with a greater proportion of animal matter. The introduction of cochineal greatly diminished the consumption of kermes. It is seldom used in this country, yet it gives a very fixed and beautiful colour to woollen cloth.

4. Lac.—This is an animal production which has been long known in India, and used for dyeing silk and other purposes. It is the nidus of the cocoon lacera, Linnaeus, and is generally produced on the small branches of the croton laevisferum. Three kinds of lac are well known in commerce—1. Stick lac is the substance or comb, in its natural state, forming a crust on the small branches or twigs. 2. Seed lac is said to be only the above separated from the twig and reduced into small fragments. Mr Hatchett, who has examined this substance with his usual skill and precision, found the best specimens considerably deprived of their colouring matter. According to the information which he received from Mr Wilkins, the silk dyers in Bengal produce the seed lac by pounding crude lac into small fragments, and extracting part of the colouring matter by boiling. 3. Shell lac is prepared from the cells, liquefied, strained, and formed into thin transparent laminae. There is also a fourth kind, called lump lac, which is obtained from the seed lac by liquefaction, and afterwards formed into cakes. The best lac is of a deep red colour; when it is pale and pierced at the top, the value is greatly diminished; for then the insects have left their cells, and it can no longer be of use as a dyestuff.

Unverdober has likewise examined lac, but his experiments throw no light upon the nature of the colouring matter. Being derived from a cocoon, as well as the colouring matter of cochineal and kermes, the probability is that it is of the same nature. In the state in which it comes to this country (that of a purple powder), it dissolves readily in boiling hot water. In this way it is employed by the dyers. Being much cheaper than either cochineal or kermes, it has in some measure superseded these dyestuffs, except when a very fine scarlet is wanted, in which case cochineal is still employed.

5. Archil.—This substance, called oreille by the French, is a violet-red paste, of which there are two varieties, one, which is the best, made in the Canary Islands, the other manufactured in the south of France. It is made from two species of lichens, the roccella and the parillus. Berthollet, who has copied Hellot, who again copied Michel, has given the following description of the mode of preparing it. The plant is reduced to a fine powder, which is afterwards passed through a sieve, and slightly moistened with stale urine. The mixture is daily stirred, each time adding a certain proportion of soda in powder, till it acquire a clove colour. It is then put into a wooden cask, and urine, lime-water, or a solution of sulphate of lime (gypsum), is added in sufficient quantity to cover the mixture. In this state it is kept; but to preserve it any length of time, it is necessary to moisten it occasionally with urine. We suspect that soda is not employed in the preparation of this dyestuff; at least it is not employed in the manufacture of cudbear, the preparation of which, being a manufacture of this country, we have often witnessed.

If we adopt the opinion of Tournefort, the preparation of archil was known to the ancient Greeks. He thinks that the purple of Amorgos, one of the Cyclades, the colour given to the famous tunics of that country, was formed by a dyestuff made from the lichen roccella.

What is called in this country cudbear, and in Germany Cudbear persio, is prepared from the lichen tartareus, and omphalodes, by a process quite similar to that employed for making pared archil. The lichen is steeped and left for some time in flat vessels moistened with ammonia distilled from putrid urine. When the purple colour is sufficiently developed, the whole is dried in the open air, and reduced to a fine powder. The manufacture of this dyestuff was begun about the year 1777, at Leith, by Mr Mackintosh and Dr Cuthbert Gordon, from which last the British name of cudbear (originally Cuthbert) is derived. Leith was found an improper place for the manufacture; but Mr Mackintosh transferred it to Glasgow, and manufactured cudbear during the rest of his life with success. He left it to his son Charles Mackintosh, Esq. who still carries it on. The lichens used were at first collected in the Highlands of Scotland; but the rocks of that country being stript of their covering, the manufacturers had recourse to Sweden and Norway, and likewise to Sardinia, from which countries prodigious quantities of the lichens were brought. There is said also to be a manufactory of cudbear in Liverpool.

Neither archil nor cudbear are capable of giving fast colours to cloth; but they are considered as indispensable by the dyers, because they greatly improve the brilliancy of some of the colours.

The nature of the substance in the lichen roccella, which furnishes the colouring matter of archil, has been erythrin investigated by Heeren, who has distinguished it by the name of erythrin. It may be obtained from the lichen by the following process: Digest the lichen for some time in alcohol, taking care not to raise the heat to the boiling point, because at that temperature a portion of the erythrin is decomposed. The alcoholic solution has a green colour. Filter it while hot, and mix it with twice its bulk of water, which will render it muddy. Raise the liquid to the boiling temperature, and introduce into it chalk in powder, until the precipitate, which was at first dispersed through the liquor, collects in flocks. This precipitate consists chiefly of roccellate of lime. The liquid must be filtered while boiling hot. During the cooling it deposits erythrin in the state of a fine powder, of a brown colour. Dissolve it in hot alcohol, digest the solution with ivory black, filter, and mix it with one and a half times its bulk of boiling water. The liquor remains at first clear, but during the cooling the erythrin precipitates nearly white.

The following process for extracting erythrin from the lichen roccella is easier than the preceding. Pour on the lichen a small quantity of concentrated ammonia, and digest for some time, stirring well, but without the application of heat. Dilute the muddy and reddish solution thus obtained with water; and then add to it some dilute solution of chloride of calcium. Roccellate of lime precipitates, and the filtered liquid has a reddish colour. Add to it a slight excess of nitric acid. The erythrin precipitates instantly, and gives the liquid the aspect of a yellowish jelly. When we heat to the boiling temperature, the erythrin is again dissolved, and it is precipitated in powder during the cooling of the liquid. It may be deprived of its brown colour by ivory black.

Erythrin is a soft powder, having usually a slight shade of red, and a slightly crystalline aspect, when obtained from a weakly acid liquid. When pure it is perfectly white. It has neither taste nor smell. At a temperature a little above 212°, it melts into a transparent liquid, which becomes hard and brittle during the cooling. If the heat be raised still higher, it froths, is partly volatilized, and partly charred; but not the least trace of ammonia can be observed to be formed. Hence we may conclude that erythrin contains no azote. When held to the flame of a candle it burns like a resin. It is scarcely soluble in cold water, and requires 170 times its weight of boiling water to dissolve it. At the temperature of 53° it dissolves in twenty-two and a half times its weight of alcohol, of specific gravity 0·825. It is soluble in 2·29 times its weight of the same alcohol at the point of ebullition. When this last solution cools, the whole is converted into a mass of the consistence of mortar. It is insoluble in ether, and little soluble in oil of turpentine. Muriatic acid has no action on it, but acetic acid dissolves it with facility when boiling hot, but lets it fall again on cooling. Both nitric acid and concentrated sulphuric acid dissolve it, but they alter its nature. The aqueous solutions of the alkalies, or their carbonates, dissolve it with facility, and the solutions are colourless. By the continued action of the alkalies, the erythrin is decomposed. When this action takes place in close vessels, an extractive substance is formed, which is soluble in water, having a bitter taste, and which Heeren on that account has called bitter of erythrin. When the action is continued in vessels to which the air has access, the red or rather violet substance is formed which constitutes the colouring matter of archil.

During the conversion of erythrin into the red matter three different substances are obtained, namely, the red colouring matter, a yellow substance, and a wine-red substance. They are first mixed or combined; but the red colouring matter may be separated by dissolving the compound substance in alcohol, evaporating the solution to dryness, and digesting the residue in ammonia. The red colouring matter remains when this solution is evaporated.

It is little soluble in water. Alcohol dissolves it, and the solution has a crimson-red colour. It is quite insoluble in ether. The alkalies and their carbonates dissolve it, and the solution has a fine deep colour. The acids throw it down from these solutions under the form of carmine red powder, but they do not precipitate it from its solution in alcohol. Heeren has shown that alcohol has the property of altering erythrin, and of converting it into a snow-white substance, to which he has given the name of pseudo-erythrin, because it does not yield the red colouring matter, but only the wine red. It has been analyzed by Liebig, who found its constituents,

| Substance | Percentage | |-----------------|------------| | Carbon | 60·810 | | Hydrogen | 6·334 | | Oxygen | 32·836 |

These correspond with

- 8 atoms carbon - 5 atoms hydrogen - 3½ atoms oxygen

Hence these atoms, or some multiple of them, must represent the composition of pseudo-erythrin.

The colouring matter of cudbear is obviously very nearly the same as that of archil. It has been slightly examined also by Heeren, who has pointed out some distinctive characters which it possesses.

In France, besides the lichen parellus, the lichen dealbatus is employed, and the archil is obtained by treating the lichens with putrid urine and lime. Robiquet has subjected the lichen dealbatus to a chemical analysis, and has extracted from it the matter which yields the red dye, and which he has distinguished by the name of orein. It constitutes white crystals, having a sweetish and nauseous taste, melts when heated, and may be distilled over without decomposition. It dissolves both in water and alcohol. It is obvious that its properties are quite different from those of erythrin; yet the process for converting it into the red dyestuff is nearly the same as for archil and cudbear.

6. Carthamus, or Safflower.—This is the petals of the blossoms of the carthamus tinctorius, a plant formerly cultivated in Germany and France; but now the dyestuff comes usually from Egypt and the countries round the eastern part of the Mediterranean, and from India.

The method of preparing the flowers of carthamus in Egypt, as it is described by Hasselquist, is the following. After being pressed between two stones, to squeeze out the juice, they are washed several times with salt water, pressed between the hands, and spread out on mats in the open air to dry. In the day-time they are covered, that they may not dry too fast with the heat of the sun, but they are left exposed to the dew of the night. When they are sufficiently dry, they are put up, and kept for sale under the name of saffron. Care should be taken afterwards not to keep it in too dry a place; for unless it is a little moist, its properties are considerably impaired.

Carthamus contains two colouring substances, a yellow substance, which is soluble in water; and as it is of no use, it is extracted by the process mentioned above, by squeezing the flowers between stones till no more colour can be pressed out. The flowers become reddish in this operation, and lose nearly one half of their weight. The other colouring matter, which is red, is soluble in alkaline carbonates, and it is precipitated by means of an acid. A vegetable acid, as lemon juice, has been found to produce the finest colour. Next to this, sulphuric acid produces the best effect, provided too great a quantity, which would alter and destroy the colour, be not employed. The juice of the berries of the mountain-ash, or rowan-tree (sorbus aucuparia, Lin.), is recommended by Scheffer as a substitute for lemon juice, and it is thus prepared. The berries are bruised in a mortar with a wooden pestle, and the expressed juice, after it has been allowed to ferment, is bottled up. The clear part, which is most acid, becomes fitter for use the longer it is kept; but this operation requires a period of some months, and can only be conducted in summer.

From the colouring matter extracted by means of an alkali, and precipitated with an acid, is procured the substance called rouge, which is employed as a paint for the skin. The solution of carthamus is prepared with crystals of soda, and precipitated with lemon juice which has stood some days to settle. After being dried on delft plates with a gentle heat, the precipitate is separated, and ground accurately with talc which has been previously reduced to a very subtle powder; and on the fineness of the talc depends the difference between the cheaper and dearer kinds of rouge.

Carthamus furnishes about five per cent. of this matter (abstracting the talc), which is the true red colouring matter. It reddens vegetable blues while moist, whether from the acid employed in throwing it down, or from its own acid properties, has not been determined. It is insoluble in water and dilute acids, but slightly soluble in alcohol. The solution has a rose-red colour, but when boiled becomes yellow. Ether is still a worse solvent of rouge than alcohol. It is insoluble in oils, both volatile and fixed; but it dissolves readily, and with a yellow colour, in alkaline leys, or alkaline carbonates. According to Dobereiner (who considers it as an acid, which he calls earthamic), soda saturated with it crystallizes in fine colourless needles, having a silky lustre, which become instantly red when an acid is added to them.

As a dyestuff, safflower affords only a fugitive colour, destroyed by exposure to the sun, and removed by washing. It is used, however, occasionally to give a red colour to silk.

7. Brazil Wood.—This wood comes from Brazil, and from Pernambuco; and in the former case is said to be the wood of the *caesalpina sapan*, *caesalpina cristis*, and *caesalpina vesica*; in the latter, of the *caesalpina echinata*. These trees are large, and rich in colouring matter. The wood is very hard, and is said to sink in water. When fresh cut it is pale, but becomes reddish by exposure to the air. Its taste is sweetish. The red colouring matter of Brazil wood is very easily acted on by chemical agents, acids rendering it yellow, and alkalis violet. Chevreul has given us the following process for extracting this colouring matter in a state of purity. Digest the raspings of the wood in water till that liquid has dissolved all the colouring matter, and evaporate the infusion to dryness, to get rid of a little acetic acid which it contains. Dissolve the residue in water, and agitate the solution with litharge, to get rid of a little fixed acid which it contains. Evaporate again to dryness. Digest the residue in alcohol: filter and evaporate to drive off the alcohol. Dilute the residuum with water, and add to the liquid solution of gelatine, till all the tannin which it contains is precipitated. Filter again, evaporate to dryness, and digest the dry mass in alcohol, which will leave undissolved the excess of gelatine that may have been added. This last alcoholic solution being evaporated, the pure colouring matter of Brazil wood remains behind.

It is soluble in water and in alcohol, but its fine red colour does not appear till all the acid which it naturally contains is saturated. Acids give it a yellow colour. The sulphuric, nitric, and muriatic acids, give it a pale dirty yellow. Fluoric acid gives it at first a yellow colour, which is gradually altered to greyish green; while the phosphoric and citric give it a fine permanent yellow colour, which might be employed for dyeing silk and wool.

For these facts we are indebted to Bonsdorff. A very minute quantity of alkali gives the infusion of Brazil wood a violet colour; it is therefore a delicate re-agent for alkalis. When neutral salts, with an alkaline base, are dissolved in the infusion of Brazil wood, it assumes a rose-red colour. Acetates act most decidedly in producing this effect. When newly precipitated alumina is agitated in this infusion, it assumes a carmine-red colour.

When Brazil wood is boiled in water, we obtain a rose-coloured solution, and the undissolved wood becomes black, but still yields to alcohol a dark-red colour. When an acid is poured into the decoction, a red precipitate falls, and the filtered liquid is yellow. Ammonia gives the decoction a purple colour, and throws down a purple precipitate. The carbonates of potash and soda render it carmine red, and throw down a precipitate of the same colour. Alum throws down an abundant carmine precipitate, but the liquid retains the same colour. The proto-chloride of tin gives a rose-red precipitate, and renders the decoction colourless.

Brazil wood is the substance from which red ink is prepared. The colour which it communicates to cloth has very little permanence; yet it is occasionally employed in dyeing cotton what are technically called chemical colours, by which is understood colours that will not resist washing. The decoction of Brazil wood, which is called juice of Brazil, is found to answer better for the process of dyeing when it has been kept some time, and has even undergone some degree of fermentation, than when it has been fresh prepared. The colour by keeping becomes of a yellowish red.

Within the last five or six years, Brazil wood has been nearly superseded by a wood imported from Africa, to which our dyers give the name of congo wood. It is richer, and gives a finer colour, than any of the varieties of Brazil wood. It is not so much affected by alkalis, nor so liable to assume a violet shade; and the yellow colouring matter with which it is mixed gives the red a more lively appearance. We have not learned the botanical name of the tree which yields this wood.

8. Logwood.—This wood is usually, on the Continent, called Campeachy wood. It is the wood of the *haematoxylin Campeachianum*, a tree which grows to a considerable size in Jamaica, and on the eastern shore of the Bay of Campeachy. Its specific gravity is greater than that of water; it has a fine grain, and is susceptible of a fine polish. Besides the colouring matter to which it owes its value, logwood contains resin and oil, which are soluble in water; acetic acid and salts, consisting of potash and lime, combined with a vegetable acid, which are soluble in water saturated with chloride of potassium. It contains also sulphate of lime, oxalate of lime, a little alumina, and some peroxide of iron and oxide of manganese. Chevreul, to whom we are indebted for a chemical examination of logwood, has given the following process for extracting its colouring matter, which he has distinguished by the name of hematin.

The raspings of the wood are digested in water of a low temperature from 122° to 131°, till everything soluble is taken up. Evaporate the aqueous solution to dryness by a gentle heat, and treat the residue with alcohol of the specific gravity 0·843, which dissolves the colouring matter, leaving a brown residue still containing colouring matter in chemical combination. Filter the alcoholic solution, and distil it till what remains becomes of the consistence of a syrup. This syrup being mixed with some water, crystals begin immediately to be deposited. Leave it for twenty-four hours to evaporate spontaneously, then decant the liquid portion from off the crystals, and wash them with a little alcohol. The decanted liquid being left to spontaneous evaporation, will yield more crystals, and finally remains a thick uncrystallizable liquid. If it be evaporated to dryness, macerate the dry mass in cold water, and evaporate afresh: more crystals are obtained, which may be purified, like the other, by washing them in alcohol. These crystals thus obtained constitute hematin, or the pure colouring matter of logwood.

They have considerable lustre, and a scarlet colour. Under the microscope they appear to constitute needles arranged in sphericles. When rubbed on a glass it appears orange by transmitted light, and white by reflected light. But if we let fall on it a drop of alcohol, it appears carmine red by transmitted, and yellow by reflected light. When put into the mouth it is at first tasteless; but after some time a sensation of astringency, acidity, and bitterness, is perceived. When heated in a retort to decomposition, it gives out among other products ammonia, from which we may conclude that it contains azote. After everything volatile is driven off, there remains fifty-four per cent. of charry matter half fused; which, when burned in the open air, leaves a quantity of lime and peroxide of iron, amounting to rather less than one per cent. of the hematin employed. Hematin requires for solution 1000 times its weight of water. By evaporation it does not yield crystals, but when very much concentrated it is converted into a confused crystalline mass. It dissolves in alcohol and ether, and the solutions have a reddish-yellow colour. It combines with the acids, which render it yellow when added in small quantity; but when in a larger proportion they give it a red colour. Sulphurous acid and carbonic acid give the solution of hematin a pale-yellow colour. Boracic acid gives it a pale-red, and phosphoric and phosphorous acid a pale-orange colour. Arsenious acid has no sensible action on it. Sulphuretted hydrogen gas renders it yellow; and if we keep a solution of hematin charged with this gas for some time in a corked phial, it loses its colour altogether; but the colour appears if we remove the gas by means of a little oxide of lead. The salifiable bases give solution of hematin a violet, purple, or blue colour. With the fixed alkalies it forms compounds perfectly saturated and soluble. The alkaline earths fall down in combination, and have a purple colour when they fall from neutral salts, and a blue colour when from sub-salts. An excess of alkali destroys the colour altogether. With the hydrated oxides of antimony, zinc, bismuth, nickel, iron, and copper, it forms blue or purple coloured compounds. The compound which hematin forms with alumina and oxide of copper at once may be fixed upon linen or cotton, and gives a blue colour like that of indigo, only it is rendered yellow by the concentrated acids, while indigo remains unchanged, unless the acid be the nitric. The protoxide of tin, when united with hematin, forms a blue-coloured compound, while its combination with the peroxide of tin is red. We see from this that the protoxide of tin possesses the characters of an alkali, while the peroxide is an acid. A solution of gelatine throws down a concentrated solution of hematin purple.

Hematin is easily altered. When a mixture of alkali and hematin is kept in vacuo, or in a well-corked phial, quite full, no action takes place; but when air has access, oxygen is absorbed, and the hematin quite destroyed in a few hours. During this action, the blue colour of the liquid changes first into red, and then into brown. The alkali becomes saturated with carbonic acid.

II.—Method of dyeing Wool Red.

All the colouring matters employed for dyeing wool red by modern dyers require a mordant to fix them. The shade of colour depends partly upon the kind of colouring matter used, partly on the mordant, and partly on the quantity of colour which the cloth is made to imbibe by the length of time that it remains exposed to the action of the dyeing liquor. The purple of the ancients, the colouring matter of which was obtained from different species of shell-fish, required no mordant; but it has already been observed that this mode of dyeing has been for ages out of use.

Madder Red.—Madder is only employed for dyeing coarse woollen stuffs; and the following is the process. The stuffs are first boiled for two or three hours with alum and tartar; they are then left to drain, slightly wrung out, put into a linen bag, and carried into a cool place, where they are to remain for some days. The quantities and proportions of the alum and tartar are varied according to the views of the dyer, and the shade of colour which is wanted. Some recommend five ounces of alum and one ounce of tartar to each pound of wool. By increasing the proportion of tartar to a certain degree, a deep and permanent cinnamon colour, instead of a red, is produced. This arises from the yellow tinge which is induced by means of the acid on the colouring particles of the madder. Others propose to diminish the proportion of tartar, and to employ only a seventh part. In conducting the process of dyeing with madder, the bath should not be brought to the boiling point; because at that temperature the fawn-coloured particles would be dissolved, and a different shade obtained from that which is desired. When the water is at that degree of temperature which the hand can bear, Hellot recommends the addition of half a pound of grape madder for every pound of wool to be dyed. It is then to be well stirred before the wool is introduced, which must remain for an hour without boiling, excepting for a few minutes towards the end of the process, that the combination of the colouring particles with the stuff may be more certain.

Madder reds are sometimes rosed, as it is called, with archil and Brazil wood. In this way they become more beautiful and velvety; but this brightness is not permanent. But madder reds, even when they are most perfect, are far inferior to those obtained from lac and cochineal, and even to that produced by kermes; but as the expense of the materials is comparatively small, they are employed, as we have already observed, for coarse stuffs.

Different authors recommend different proportions of madder. Poerner proposes to employ one third of the weight of the wool, while Scheffer limits the quantity to one fourth. In one process, Poerner added to the alum and tartar a quantity of solution of tin equal in weight to the tartar, and after two hours boiling allowed the cloth to remain in the bath, which had been left to cool for three or four days. He then dyed it in the usual way, and thus obtained a fine red. According to another process, he prepared the cloth by the common boiling, and dyed it in a bath slightly heated, with a larger proportion of madder, tartar, and solution of tin. The cloth remained twenty-four hours in the bath; and when it had become cold he put it into another bath, made with madder only, where it remained for twenty-four hours. By this process he got a fine red, somewhat brighter than the common, but inclining a little to yellow. Scheffer informs us that he obtained an orange-red by boiling wool with a solution of tin and one fourth of alum, and then by dyeing with one fourth of madder. A cherry colour is obtained, according to Bergman, by dyeing with one part of a solution of tin and two of madder, without previously boiling the wool. By exposure to the air this colour becomes deeper. By boiling the wool for two hours with one fourth of sulphate of iron, then washing it, and afterwards immersing it in cold water with one fourth of madder, and then boiling for an hour, the result is a coffee colour. But if the wool has not been soaked, and if it be dyed with one part of sulphate of iron and two of madder, the colour is a brown approaching to red.

When sulphate of copper is employed as the mordant, the madder dye yields a clear brown, inclining somewhat to yellow; and a similar colour may be produced by dyeing the wool, simply soaked in hot water, with one part of sulphate of copper and two of madder. But when this mordant and dyestuff are used in equal proportions, the yellow is somewhat more obscure, approaching to green; and in both these instances exposure to the air does not produce a darker colour. Berthollet informs us that he employed a solution of tin in various ways, both in the preparation and the application of the madder; and by the use of different solutions of tin, he found, that although the tint was somewhat brighter than what is obtained by the common process, it was always more inclined to yellow or fawn colour.

Scarlet.—The finest and most splendid of all colours is scarlet. This, like other colours, is of various shades, according to the quality and proportion of the colouring matter employed. The scarlet dye is communicated to wool- len stuffs by means of cochineal, the history and properties of which we have already detailed. The Mexicans, as appears from their history, employed alumina as the basis or mordant to fix the colour of cochineal; and previous to the discovery of the solution of tin, the use of the same substance seems to have prevailed in Europe. The fine colour obtained from the latter received, as we have already mentioned, different names in different places; as that of bone dye in England, scarlet of the Gobelins in France, and in Holland Dutch scarlet.

In the process for dyeing scarlet two operations are necessary. The first is denominated the boiling, and the second is distinguished by the name of finishing or reddening. The operation of boiling, which is the first part of the process, is conducted in the following manner:—For one hundred pounds of cloth, six pounds of pure tartar are added to the water, which is made pretty warm. The bath is then to be briskly stirred; and when the heat has increased a little more, half a pound of powdered cochineal is to be added, and the whole is then to be well mixed. The next moment five pounds of a very clear solution of tin are to be poured in and carefully mixed. When the bath begins to boil, the cloth is introduced, and briskly moved for two or three turns; after which it is moved more slowly. The boiling having continued for two hours, the cloth is taken out, exposed to the air, and carried to the river to be well washed.

In the preparation of the second bath, which is for the reddening, the boiler is to be emptied, and when the bath has just reached the boiling point, five pounds and three quarters of cochineal, previously powdered and sifted, are to be added. These are to be carefully mixed; and after having ceased stirring, when a crust has formed on the surface, and opened of itself in several places, thirteen or fourteen pounds of solution of tin are poured in. Should the bath during the boiling rise above the edge of the boiler, it may be cooled with a little cold water. This solution being well mixed, the cloth is put in, and two or three times quickly turned. It is then boiled in the bath for an hour, taking care to keep it under the surface. It is afterwards taken out, exposed to the air, and, when it has cooled, washed in the river and dried.

There are no determinate proportions of cochineal and solution of tin in either of these operations. Hellot informs us that some dyers employ two-thirds of solution of tin and one fourth of cochineal in the boiling or first operation, and the other one third of the solution of tin with the remaining three fourths of the cochineal in the second operation, or the reddening. He adds farther, that the use of tartar gives a greater degree of permanency to the colour, provided the proportion do not exceed one half the weight of the cochineal employed. According to Berthollet, several dyers at present adopt this practice. Tartar, he observes, promotes the solution of the colouring matter; and this effect is greater when it is ground with the cochineal, after which it is found that the residuum is more completely exhausted. But this consideration is of inferior consequence when the operations are successively performed, because any colouring matter that may remain in the residuum is employed in the next operation. It ought not, however, to be overlooked, that the tartar communicates to the colour a rosy hue.

It is the practice of some dyers not to remove the cloth out of the boiling. They merely refresh it, and perform the operation of reddening in the same bath. When this is done, the infusion of cochineal, made in a separate vessel, and mixed with the proper proportion of solution of tin, is added. By conducting the process in this way the scarlet is supposed to be equally fine, and there is a considerable saving of time and fuel.

To give scarlet the bright lively red, which, as it approaches to the colour of fire, has been distinguished by the name of fiery scarlet, a yellow tinge is communicated by boiling fustic in the first bath, or by adding a little turmeric to the cochineal. A larger proportion of the solution of tin also produces this yellow shade, but it renders the cloth harsh, and limits the action of the colouring matter. The use of fustic or turmeric, therefore, although the colour obtained from them is not permanent, is preferable to an excess of the solution of tin. When these substances are used, the inside of the cloth, when it is cut, appears yellow; but in the ordinary processes, the cochineal, it is found, does not penetrate the cloth, for when no other substance is employed the cloth is internally white.

The use of tin boilers is recommended in dyeing scarlet. Tin and let. When copper boilers are employed, the acid acts on copper the metal, and thus forming a solution, injures the beauty boilers, of the colour. Tin boilers, however, are attended with several inconveniences. It is difficult to procure them of sufficient size, and they are apt to be melted by the incandescent continuance of the fire after they have been emptied. In the use of copper boilers there are several necessary precautions. They must be kept very clean, the acid liquor should not be allowed to remain in them for any length of time, and some contrivance should be adopted to prevent the cloth from touching the metal, either by using a net or a wicker basket.

Different proportions of materials, we have observed, are recommended by different authors. For the boiling, Scheller proportions directs an ounce and a half of solution of tin, with an equal quantity of starch, and as much tartar, to every pound of dyes cloth. The effect of the starch is to give more uniformity to the colour. When the water boils, a dram of cochineal is to be added; it is then to be well stirred, and after the wool is introduced, to be boiled for an hour, taken out, and washed. The proportions for the reddening bath, in which the wool is to be boiled half an hour, are half an ounce of starch, three fourths of an ounce of solution of tin, half an ounce of tartar, and seven drachms of cochineal. In Scheller's process, it may be observed, the proportion of solution of tin is smaller than in that of Hellot, but the quantity of tin in the solution of the former is greater than in that of the latter.

Poerner has described three principal processes, according to the variety of the shade of the scarlet. He uses no process cochineal in the boiling; the materials of which are one ounce and six drachms of tartar, and an equal weight of solution of tin, the latter being added after the tartar is dissolved, for every pound of cloth. As soon as the boiling has commenced, the cloth is introduced, and it is boiled for two hours. For the reddening of the first process he employs two drachms of tartar and one ounce of cochineal, adding gradually afterwards two ounces of solution of tin. For the reddening of the second process the same quantity of cochineal and solution of tin, without any tartar, is employed. In the reddening of the third process, two drachms of tartar with one ounce of solution of tin, one ounce of cochineal, and two ounces of common salt, are directed to be used. The colour produced in the first process has the deepest shade, that of the second is more lively, while that of the third is paler and brighter.

By the use of tartar in the reddening in different proportions, various shades of scarlet may be obtained. When shades it is employed, the shade is deeper and fuller; but when it is entirely omitted, the scarlet approaches to an orange colour. The shade of colour also is subject to considerable variety, from the different degrees of strength of the solution of tin. To ascertain this effect, Berthollet made a number of experiments. He found that a solution of tin, composed of sixteen parts of nitric acid, two of muriate of ammonia, and three of tin, produced a deeper shade than when the proportions of the acid and muriate of ammonia were equal, with only two parts of tin. The last proportions, he observes, succeeded best. Four parts of water were mixed with the solution. When the proportion of muriate of ammonia amounted only to half a part, the colour was brighter, and inclining to orange.

Common salt has the effect of increasing the brightness of scarlet, while it is also attended with the advantage of causing the colour to penetrate deeper into the cloth. It seems difficult to explain why common salt, which gives a deeper shade to the colour of the infusion of cochineal, and indeed produces a similar effect on colours in general, should diminish the intensity of the colour of scarlet. The proportion of common salt mentioned above is, according to Poerner, the greatest that can be employed. When less is used, the shade, though lighter, is more agreeable. By adding five ounces of white sugar to the ingredients of the second process, a fine colour, which is always lighter than that of the first process, will be obtained. The colour, it is said, is more permanent, and the shade more agreeable, when the cloth is left twenty-four hours in the boiler after it has cooled.

For dyeing fine woollen cloth the lac dye is commonly used. It comes to the dyer in the state of a fine powder, having a brownish-red colour, inclining to violet. It contains much less colouring matter than cochineal, but is incomparably cheaper. To dye forty-three pounds of fine woollen cloth, six pounds of lac, three pounds of cream of tartar, and five pounds of tin mordant are put into a dyeing vessel, either of tin, or at least lined with tin, with a sufficient quantity of water. The whole is brought to the boiling temperature, and after it has boiled briskly a sufficient time to dissolve the colouring matter, the cloth is passed through it for about an hour, or till it has acquired the requisite depth of colour.

The tin mordant used is made by dissolving two ounces of tin in thirty pounds of aquafortis mixed with one pound of muriatic acid. The solution is transparent, and it is kept in well-corked bottles for use. The tin is doubtless in the state of protochloride, though it sometimes also gets into the state of perchloride. Either state will answer, but in the second case the dyeing process is much slower, the cloth not seeming to imbibe the perchloride of tin so rapidly as the protochloride. From the above proportions, it is obvious that to dye forty-three pounds of woollen cloth scarlet, one third of an ounce of tin converted into protochloride is sufficient. This is rather less than 146 grains of tin; so that each pound of the woollen cloth combines with not more than 3-4 grains of tin. It is obvious from this that the particles of tin must be exceedingly minute indeed, otherwise 3-4 grains of tin could not be so minutely divided as to cover the surface of a pound weight of woollen cloth.

When the dyer wishes the scarlet to assume a brighter shade, he sometimes adds a little quercitron bark, which, by the yellow colour which it induces, adds materially to the brightness of the colour. This plan was first suggested by Dr Bancroft, and it has been since pretty generally acted on.

Dr Bancroft recommended the tin mordant to be prepared by dissolving tin in muriatic acid mixed with one fourth of its weight of sulphuric acid. This solution, he says, answers very well, and is much cheaper. We cannot find, however, that any of the dyers in this country follow that process. We can hardly think that the present method of using so much nitric and so little muriatic acid is a good one. The object being to obtain a protochloride of tin, one would think that muriatic acid would be a better vehicle. Tin dissolves in this acid very well, and the protochloride of tin formed in this way is easily obtained in crystals. But the tin mordant, as prepared by the dyers, contains a great excess of nitric acid; and we cannot avoid suspecting that this excess is connected with the shade of scarlet produced. The nitric acid doubtless renders a part of the colouring matter of the lac yellow, and thus changes the dark crimson colour natural to this dyestuff into scarlet.

Cochineal is still employed to a considerable extent in dyeing the finest kinds of woollen cloth scarlet. The process is precisely the same as when lac is employed, remembering only that cochineal is much richer in colouring matter than lac, and that therefore a smaller quantity will serve. Dr Bancroft introduced the method of putting the cochineal, the tin mordant, and the tartar into the dyeing vessel at once, and dissolving them all together in water before the cloth is passed through the liquid; and this method is pretty generally though not universally followed.

Dr Bancroft's method of using quercitron bark to supply the place of a portion of the cochineal, is likewise pretty generally followed. The price of cochineal, in consequence of the introduction of the lac dye, has sunk from thirty shillings the pound to about nine shillings and sixpence. This makes the saving not so considerable in point of expense as it was when Bancroft wrote, though even at present it is an important saving.

To produce different shades of scarlet, and the other colours which are derived from it, all that is necessary is to vary the proportions of cochineal, tartar, and solution of tin; and for the shades which incline most to yellow, the addition of quercitron bark or fustic is requisite. The use of the tartar is to deepen the colour, and the solution of tin produces a shade of orange. When the shade of colour required to be communicated to the stuff is light, the time of continuing the process must be shortened.

Crimson.—The processes which are employed to dye wool a crimson colour are two. The stuff is either dyed crimson at once, or the crimson shade is communicated to it after being previously dyed of a scarlet colour. To dye crimson by a single process, a solution of two ounces and a half of alum and an ounce and a half of tartar for every pound of stuff, is employed for the boiling, and the stuff is afterwards to be dyed with an ounce of cochineal. It is usual also to employ solution of tin, but in smaller proportion than for dyeing scarlet. The processes employed, it is scarcely necessary to observe, must vary according as the shade wanted is deeper or lighter, or more or less distant from scarlet. Common salt is also employed by some in the boiling. To render the crimson deeper, and to give it more bloom, arsill and potash are frequently used; but this bloom, it ought to be observed, is extremely fugacious. By adding tartar and alum, the boiling for crimson is sometimes prepared after a scarlet reddening; and it is said that the colour possesses more bloom when both the boiling and reddening are made after scarlet, than when the crimson is dyed in a fresh bath prepared on purpose. In dyeing these colours the wild cochineal may be employed; but as it contains a smaller proportion of colouring matter, the quantity must be greater.

Different substances, as the alkalies, alum, and earthy or by salts in general, convert the colour of scarlet to crimson, which is the natural colour of cochineal. To effect this, the stuff previously dyed scarlet is boiled for an hour in a solution of alum, the strength of which is to be regulated by the depth of shade required. In conducting this process, it is necessary to observe, that water impregnated with earthy salts has a considerable effect in varying the shade, so that the quantity of alum employed must be proportioned to the purity of the water. Heliot tried soap, soda, potash, and some other substances, and although they produced the crimson, yet it was of a deeper shade, and had less lustre, than what was produced by means of alum. Ammonia produced a good effect, but, from its great volatility, a considerable proportion must be put into the bath, moderately heated, with a little sal ammoniac, and an equal quantity of potash. By this process the stuff became of a bright rosy colour, and thus rendered a smaller quantity of cochineal necessary. Poerner directs the stuff previously dyed scarlet, to remain twenty-four hours in a cold solution of sal ammoniac and potash.

To produce crimsons, as well as scarlets, in half grain, madder is to be substituted for half the quantity of the cochineal; or in other proportions, according to the shade desired. The same boiling is given as for scarlet in grain, and the other parts of the process are to be conducted as for reddening the scarlet or crimson. Even the common madder red assumes a greater degree of lustre when the boiling is made after the reddening for scarlet.

At present we are not aware that kermes is ever employed by the dyers in this country. The use of this dye-stuff seems to have been completely superseded by cochineal and lac dyes. Certainly the colour given by kermes is not so fine as that given by these substances, but it has the advantage of being exceedingly durable.

III.—Method of dyeing Silk Red.

Madder Red.—The colour which is obtained from madder does not possess sufficient brightness for dyeing silk. We shall here, however, describe some of the processes which are employed for this purpose. That of De la Folic is the following: Half a pound of alum is to be dissolved in each quart of hot water, and two ounces of potash are afterwards to be added. When the effervescence has ceased, and the liquor has become clear, the silk must be kept in it for two hours, after which it is to be washed and put into the madder-bath. The silk which is dyed in this way becomes more beautiful by means of the soap proof. The process of Scheffer is somewhat different. For each pound of scoured silk he directs a solution of four ounces of alum and six drachms of chalk to be prepared. When the sediment has formed, the solution is to be decanted, and having become quite cold, the silk is immersed in it, and left for eighteen hours. It is then taken out and dried, and afterwards dyed with an equal weight of madder. The colour thus obtained is of a dark shade. Mr Guhlliche describes another process. For every pound of silk he proposes a bath of four ounces of alum and one ounce of solution of tin. When the liquor has become clear it is decanted, and the silk carefully soaked in it for twelve hours, after which it is to be immersed in a bath with half a pound of madder softened by boiling with an infusion of galls in white wine. The bath is to be kept moderately hot for an hour, and then made to boil for two minutes. The silk, being taken from the bath, is to be washed in a stream of water, and dried in the sun. The colour thus obtained is very permanent. By leaving out the galls it is clearer. The brightness of the first colour may be considerably increased by passing the stuff through a bath of Brazil wood, to which one ounce of solution of tin is added. In this way the colour becomes extremely beautiful and durable.

Silk is sometimes dyed with Brazil wood, and the colour thus obtained has been distinguished by the name of false crimson, to distinguish it from the more durable colour which is produced by cochineal. The silk, after being boiled with soap, is to be alummed. It is then to be refreshed at the river, and dipped in a bath more or less charged with Brazil juice, according to the depth of shade required. If pure water be employed, the colour will be too red for crimson; but to remedy this, the stuff may be passed through a weak alkaline solution, or a little alkali may be added to the bath, or the stuff may be washed in hard water till it has acquired the proper shade. To deepen the shade of false crimsons or dark reds, the solution of logwood is added to the Brazil bath, the silk being previously impregnated with the latter; or a little alkali may be added, according to the shade required.

The crimson produced by cochineal is called grain crimson. With cochin, to distinguish it from false crimson. The silk, being chineal, well cleansed from the soap at the river, is to be immersed in alum liquor of the full strength, and to remain for a night. It is then to be washed and twice beetleed at the river. The bath is prepared by filling a long boiler two thirds with water, to which are added, when it boils, from half an ounce to two ounces of powdered white galls for every pound of silk. When it has boiled for a few moments, from two to three ounces of cochineal, also powdered and sifted, for every pound of silk, are put in, and afterwards one ounce of tartar to every pound of cochineal. When the tartar is dissolved, one ounce of solution of tin is added for every ounce of tartar. In the preparation of this solution of tin, the following proportions are recommended by Macquer. For every pound of nitric acid two ounces of sal ammoniac, six ounces of fine grain tin, and twelve ounces of water, are employed. When these ingredients are mixed together, the boiler is to be filled up with cold water; and the proportion of the bath for every pound of silk is about eight or ten quarts of water. In this the silk is immediately immersed and turned on the winch till it appear to be of a uniform colour. The fire is then increased, and the bath is kept boiling for two hours, taking care to turn the silk occasionally. The fire is afterwards put out, and the silk put into the bath, where it is allowed to remain for a few hours longer. It is then taken out, washed at the river, twice beetleed, wrung, and dried. Two processes are recommended by Scheffer and Macquer. In that of the former, a greater proportion of cochineal is employed in the dye-bath; but in that of the latter, a yellow ground is previously communicated to the silk. The colour which is thus obtained resists the action of soap, and is more durable than that which is produced by means of carthamus.

To obtain other shades of red, the above processes must be varied. If, after the silk has been wrung out of the solution of tin, it is steeped for a night in a cold solution of alum, in the proportion of one ounce to a quart of water, wrung, and dried, then washed and boiled with cochineal, it will only appear of a pale poppy colour; but a fine poppy red may be produced by steeping it twelve hours in the solution of tin, diluted with eight parts of water, then left all night in the solution of alum, washed, dried, and passed through the two baths of cochineal, taking care to add to the second bath a small quantity of sulphuric acid. The same colour may be produced by dyeing the silk previously with annota, and then passing it successively through a number of baths prepared with an alkaline solution of carthamus, to which lemon juice has been added, till it acquire a fine cherry-colour. To brighten the colour, the silk, after being dyed, may be immersed in hot water acidulated with lemon juice.

Other shades of red, as a cherry red, and flesh red, are also produced by carthamus. For a cherry red it is not red, &c. necessary that the stuff be previously dyed with annota, and the proportion of colouring matter is smaller. A flesh-red colour is obtained by adding a little soap to the bath, which has the effect of softening the colour, and of retarding the action of the colouring matter on the stuff. To produce dark shades, it is sometimes usual to mix archil, and by this means the expense is diminished.

Scarlet.

Those who have produced a colour on silk which comes nearest to scarlet, Berthollet observes, begin with dyeing the silk crimson. It is then dyed with carthamus, and lastly it is dyed yellow without heat. By this process a fine colour is obtained; but the dye of the carthamus is not permanent, as it is destroyed by the action of the air, and the colour becomes deeper. The following is Dr Bancroft's process. In a solution of muri-o-sulphate of tin, diluted with five times its weight of water, the silk is to be soaked for two hours; and after being taken out, it is to be wrung and partially dried. It is then to be dyed in a bath prepared with four parts of cochineal and three of quercitron bark. In this way a colour approaching to scarlet is obtained. To give the colour more body, the immersion may be repeated both in the solution of tin and in the dyeing bath; and the brightness of the scarlet is increased by means of the addition of carthamus. A lively rose colour is produced by omitting the quercitron bark, and dyeing the silk with cochineal only; and by adding a large proportion of water to the cochineal, a yellow shade is obtained, which changes the cochineal to the compound scarlet colour.¹

IV.—Method of dyeing Cotton and Linen Red.

The dyestuff usually employed to give a red colour to cotton and linen is madder. It is easier to dye cotton than linen; but as the processes are the same for each, one general description will apply to both. There are two kinds of madder red; the one is called simple madder red, and the other, which was originally invented in the Levant, is distinguished in this country by the name of Turkey red. This last constitutes by far the brightest and most beautiful and permanent red which is communicated to cotton; we shall therefore proceed to give a somewhat particular account of the process.

The method was first put in practice in Glasgow about forty years ago, by M. Papillon, a French gentleman, who established a Turkey-red dye-work along with Mr Macintosh. He made an agreement with the commissioners and trustees for manufactures in Scotland, that the process was to be by them published for the benefit of the public at the end of a certain term of years. The period agreed upon having expired in 1803, the trustees laid a minute account of the different processes before the public. Since that period Turkey-red dyeing has been conducted in Glasgow upon a very extensive scale. Different individuals, possessed of both chemical skill and considerable sagacity, have studied the different parts of this very complicated method of dyeing. The effects of each individual operation have been carefully investigated, and the whole has been somewhat shortened and simplified, though it still constitutes the most complicated process in the whole art of dyeing. The Turkey-red dye is practised by a considerable number of persons in Glasgow; but the oldest, and perhaps the most extensive establishment, is that of Henry Monteath and Company at Rutherglen Bridge. The character of that house has been long established, and the beauty of their Turkey-red dye is known and appreciated in every part of the globe where British manufactures are known. From Glasgow the Turkey-red dye has gradually made its way into Lancashire.

Cotton cloth which is to receive the Turkey-red dye is never bleached beforehand; because it has been found that the first parts of the processes succeed better with unbleached than with bleached cloth.

1. The first step of the dyer is to remove the weaver's dressing. This is done by steeping the cloth in a weak steep alkaline ley. To this the technical name of the rot steep is given. From four to five pounds of caustic potash are generally employed for every 100 lbs. of cotton cloth. The temperature of the solution is from 100° to 120°, and the cloth is kept in the steep for twenty-four hours, and then well washed.²

2. From seven to ten pounds of carbonate of soda are dissolved in a sufficient quantity of water to keep the cloth (supposed always to weigh 100 lbs.) wet. In this ley the cloth, previously deprived of the weaver's dressing, is boiled for some time.

3. The process which we are now going to describe is the one upon which the goodness of the Turkey-red dye steep depends more than upon any of the others. Without it the dye cannot be produced upon new cloth; but when cloth which has been frequently washed with soap is to be dyed (an old cotton shirt, for example), this process may be omitted altogether. It is evident from this that soap communicates to cotton cloth the same properties as the process which we are now going to describe.

A liquor is composed of the following ingredients:

- 1 gallon of gallipoli oil, - ½ gallon of soft sheep dung, - 4 gallons of solution of carbonate of soda, of the specific gravity 1·06, - 1 gallon of solution of pearl ash, of the specific gravity 1·04,

mixed with a sufficient quantity of cold water to make up twenty-two gallons. The specific gravity of this liquor should be from 1·020 to 1·025.

This liquor has a milk-white appearance, and is in fact a kind of incipient soap. It is put into a large wooden open cylindrical vessel, called the liquor tub (see Plate CCVI. fig. 1 and 2), and is kept continually in a state of agitation by a kind of wooden levers, driven round in it by machinery put in motion by the steam-engine. This liquor is conveyed by a tin pipe to the padding machine, which is situated in an apartment below. Several sections of this machine are given in the same plate, fig. 3, 4, and 5. A kind of trough in this machine is kept always full of the milky liquor, and the pieces of cloth to be dyed are made to pass through this liquid, and are thoroughly soaked with it.

By this process the cloth is impregnated with the soapy matter, and the longer this matter is left undisturbed on the cloth, the better does it take the dye. Fourteen days is the least period that this impregnation is allowed to remain.

The sheep dung gives the cloth a dark-green colour, and is found materially to assist the bleaching which the cloth afterwards undergoes. This bleaching goes on much more rapidly with than without the sheep dung, especially when the cloth is exposed on the grass between the different operations. In what way the sheep dung contributes to this acceleration has not been determined, but the fact is certain.³

4. When the weather is favourable, the cloth, after be-

¹ Philosophy of Permanent Colours, 312. ² In general the alkaline ley of No. 9 is worked up in this process, and when this is done less potash is required. ³ No advantage has been found to result from using the alkalies caustic in this process; and a mixture of potash and soda answers much better than soda alone. ing impregnated with the oleaginous liquor, is spread up- on the grass to dry. But should the weather be rainy, as it would not do to allow the oleaginous liquid to be washed out by the rain, the goods are dried in the stove.

5. After the cloth has been dried in the stove, it is a second time impregnated with the oleaginous liquid de- scribed in No. 3, by means of the padding machine. It is then spread on the grass for some hours if the weather be favourable, and ultimately dried in the stove.

The impregnation with the oleaginous liquor, the ex- posure on the grass, and the stove drying, are repeated a third time. When the weather is rainy, which prevents exposure on the grass, and obliges the workmen to dry the cloth at once in the stove, the impregnation with the oleaginous liquor is sometimes repeated a fourth time.

Upon the sides of the tubs in which the oleaginous liquor is kept, a white solid crust gradually accumulates. This matter being examined, was found to consist almost entirely of phosphate of lime. It was doubtless derived from the sheep dung with which the saponaceous liquid was mixed.

6. The next process is to steep the cloth in a weak so- lution of pearl ash, of the specific gravity 1-0075 to 1-01, heated to the temperature of 120°. From this liquor it is wrung out and again dried.

7. A mixture is now made of the following substances: 1 gallon gallipoli oil, 3 gallons soda ley of specific gravity 1-06, 1 gallon caustic potash ley of specific gravity 1-04, diluted with as much water as will make up the whole to twenty-two gallons. In this liquid, which is milky, like the preceding, and which contains an imperfect soap, the cloth used formerly to be tramped with the hand, and then wrung out. It is now soaked with the liquid by means of the padding machine, in the manner described under No. 3.

If the weather be fine, the cloth thus impregnated with the soap is exposed on the grass. It is then dried in the store.

8. The above process (No. 7) is repeated thrice; and after each soaking in the saponaceous liquor, the cloth is exposed on the grass for some hours, and then dried in the store.

9. The cloth, thus so many times soaked in the sapon- aceous liquor, is now steeped in a mixed ley of pearl ash and soda of the specific gravity from 1-01 to 1-0125, heat- ed to the temperature of 120°. After being taken out of the steep, and allowed to drain for a few hours (taking care to preserve the liquor), the cloth is well washed. The object of this process is to remove any superfluous oil with which the cloth may be impregnated, the object being that all the oil adhering to the cloth should be in combination with an alkali. About half the alkali used in this process disappears during the steeping. The remain- ing liquor, which is about half as strong as at first, is re- served for future use. The cloth thus washed clean is dried in the store.

10. The preceding washing is necessary for the suc- cess of the next operation, called the galling; for the nutgall liquor will not be imbibed by the cloth unless it be thoroughly freed from all uncombined oil, which would give it a greasy feel. If the first steeping in alkali and washing has not fully accomplished this necessary object, they ought to be repeated.

For the galling, eighteen pounds of Aleppo galls are to be boiled for four or five hours in twenty-five gallons of water till it is reduced to about twenty gallons; and the liquid being now passed through a sieve, is sufficient for impregnating 100 lbs. of cloth with the requisite quantity of nutgalls. Of late years, sumach from Sicily has been substituted for nutgalls, thirty-three lbs. of sumach being considered as equivalent to eighteen lbs. of nutgalls. Sometimes a mixture of nine lbs. nutgalls and sixteen and a half lbs. of sumach is employed.

Through this decoction the cloth is either tramped by the hand, or it is passed and soaked in it by means of the padding machine. The temperature of the decoction should be from 80° to 100°. It is unnecessary to steep the cloth in the gall liquor; a complete soaking is all that is necessary. The cloth, thus soaked in a decoction of fustic, comes out dyed yellow, a colour which serves to improve the madder red by rendering it more lively.

11. The next process is to fix the alumina mordant upon the cloth. This step is essential, because without- it the madder dye would not remain fixed in the cloth, but would be easily washed out. Accordingly the depth of the shade of red depends entirely upon the quantity of alumina fixed on the cotton. In a preceding part of this article we have stated the quantity of alumina fixed by this process upon the surface of a square yard of cloth.

In this country common alum is usually employed; but in many parts of the Continent they use acetate of alumina. The high price of that article prevents its employment in Britain. Acetate of alumina, however, is made in this coun- try by the chemical manufacturers, and largely used by the calico-printers. It is made by mixing acetate of lime (obtained by saturating the acetic acid formed when wood is distilled with lime) with a solution of alum, and after- wards drawing off the clear liquor; or by mixing acetate of lead with solution of alum, though that process is more expensive.

Alum (as has been explained under the article Alum) is a double salt, composed of: 3 atoms sulphate of alumina, 1 atom sulphate of potash, 25 atoms water.

To form the alum liquor used by the Turkey-red dyers: To a solution of alum in water of the specific gravity 1-04 as much pearl ash, soda, or chalk is added as is sufficient to precipitate the alumina contained in the alum. Through this muddy liquor, which should have a temperature of from 100° to 120°, the cloth is passed and steeped for twelve hours. The alumina, in the state of extreme divi- sion which it has when thus newly precipitated, is readily imbibed by the cloth, and unites with the fibres of the cotton.

12. The cloth thus united to alumina is stove dried, and then washed out of the alum liquor.

13. These essential preliminary steps having been taken, the cloth is ready for being dyed.

From one to three lbs. of madder reduced to the state of powder for every pound of cloth is employed, the quan- tity depending upon the shade of colour wanted. The cloth is entered into the boiler when the water is cold. It is brought to boil in one hour, and the boiling is con- tinued for two hours. During the whole of this time the cloth is passed through the dyeing liquor by means of the winch.

For every twenty-five lbs. of cloth dyed, one gallon of bullock's blood is added. This is the quantity of cloth dyed at once in a boiler. This addition of blood is indis- pensable for obtaining a fine red colour. Various attempts have been made to dispense with the use of blood in Tur- key-red dyeing, but hitherto they have been unsucces- sful. No satisfactory explanation of the way in which the blood acts has been given. For our own parts, we are dis- posed to consider the colouring matter of the blood as the useful ingredient. It is probably fixed upon the cloth to a certain extent, and by its fine scarlet tint it is obvious that it must improve the colour of madder red. 14. After the cloth has been thus dyed, it was formerly customary to steep it in a solution the same as that described in No. 7. This was called the *clearing* process. It is now generally dispensed with, and is unnecessary if the cloth has been well cleaned before the galling process. The object of it is merely to dissolve any greasy matter which may continue attached to the cloth, and to form a soap with it, which assists in the subsequent process.

15. Madder contains two colouring matters, a brown and a red. Both are fixed upon the cloth by the dyeing process. The consequence is, that the cloth has a dirty brownish-red colour, which is anything but agreeable. Fortunately the brown colouring matter is not nearly so fixed upon the cloth as the red colouring matter. The next process, called the *clearing* process, is to get rid of the brown colouring matter. For this purpose the cloth is boiled from twelve to fourteen hours, in a mixture of five pounds of soda, eight pounds of soap, and sixteen to eighteen gallons of the residual liquor of No. 9, with a sufficient quantity of water. These quantities are supposed to be employed to clear a hundred pounds of cloth. By this process the brown colouring matter is almost wholly removed, and the cloth begins to assume the fine tint which distinguishes Turkey-red dyed cloth.

16. The next process serves not merely to remove the brown colouring matter more completely, but also to improve the shade of red. Five or six pounds of soap, and from sixteen to eighteen ounces of protochloride of tin, in crystals, are dissolved in water, in a globular boiler, into which the cloth is put. The boiler is then covered with a lid which fits close, and the boiling is conducted under the pressure of two atmospheres, or at the temperature of $250^\circ$. The boiler is furnished with a safety valve and a small conical pipe, the extremity of which has an aperture about $\frac{3}{8}$ths of an inch in diameter, from which there issues a constant stream of steam during the operation. We have given a section and elevation of this boiler in Plate CCVII. fig. 8 and 9; and in fig. 10 a plan of its top, and in fig. 11 of its lid. The use of the salt of tin is to give a shade of scarlet to the cloth. The oxide of tin seems to combine with the oleaginous acid of the soap, and this insoluble soap unites with the red colouring matter of the madder fixed upon the cloth, and improves the shade of colour.

17. After these processes, the cloth is spread out on the grass and exposed to the sun for a few days, which finishes the clearing. It is seldom that recourse is had to a bleaching liquor, consisting of a solution of chloride of lime in water, especially when a salt of lime is used in the cleaning process. When this method is employed, however, one gallon of the solution of chloride of lime, of the specific gravity 1-015, is mixed with twenty gallons of pure water. The cloth is immersed in this dilute solution from five to ten minutes, which is sufficient for completing the clearing.

Such are the different steps in fixing this beautiful and permanent colour, as practised in the principal works in Glasgow. Many attempts have been made to shorten these tedious processes, but hitherto these attempts have been unsuccessful. The impregnation with oil, or rather with soap, is essential, as is evident from this, that if one, two, or three of these operations be omitted, the red is inferior in proportion to the number of omissions.

Cloth bleached by chloride of lime does not produce a good red. Probably the fibres of the cotton wool are combined with lime, or rather sulphate of lime, which, by decomposing the oleaginous soap, prevents it from being deposited upon and combining with the cloth. But cloth bleached by the old process, namely, boiling in ley or soap, and exposing to the action of the sun, answers perfectly, and will produce as good a red as when unbleached cloth is used; but there would result no saving from bleaching the cloth in this way before commencing the impregnation with the oleaginous soap, because the bleaching is effected betwixt the oil operations by exposing the cloth on the grass.

The colour would be as good without the galls or such as with them. But there would be considerable difficulty in sufficiently impregnating the cloth with the solution of alum without its being previously passed through the gall decoction, and more particularly if the cloth be in the least degree greasy. The use of the galls, then, is to facilitate the fixation of the alumina upon the cloth.

Alumina is essential to the fixation of the colour; for without it the madder dye would be fugitive, and would disappear whenever the cloth was washed. The subsequent clearing operations would completely remove both the colouring matters of the madder, unless it were cleared along with a quantity of cloth that had received alumina, and been dyed a deep red. In that case the unalumined cloth will receive a little alumina from the alumined portion. This will serve to fix the colour; but as the quantity of alumina which in such a case is imbibed is very small, the red colour will be very pale. It is in this way that the two shades of red, the deep and the pale, which are often seen upon garments and furniture dyed Turkey red, are given. These two shades, by their contrast, frequently add considerably to the beauty of the pattern. The fustic, as well as the tin, probably serves to render the red colour more lively by the shade of yellow which they superinduce.

The three essential processes in the Turkey-red dyeing are, the impregnation with oleaginous soap, the impregnation with alumina, and the dyeing with madder. The last communicates the colour, the second fixes the colour, and the first gives beauty to the colour.

For the better understanding of the Turkey-red processes, we have got drawings made of the principal machinery used.

Figs. 1 and 2, Plate CCVI., exhibit a section and plan of the liquor tub, in which the mixture of oil and alkali is put, with its agitators to prevent the oil from separating and swimming on the surface. From the liquor tub (which is placed in an upper room) the liquor passes by a tin pipe to the padding machine, represented in various ways in figs. 3, 4, and 5.

It consists essentially of a box for holding the liquor, through which the cloth passes; and afterwards it goes between two rollers, the distance between which regulates the quantity of liquor which the cloth retains.

a, is the lapper for folding the cloth. b, a compound lever for regulating the pressure. c, the box for containing the liquor. d, a frame or *scrae* for laying the cloth on before it passes through the liquor. e, pulleys for moving the lapper; and f, the cylinders between which the cloth passes. They regulate, by their distance from each other, the quantity of liquor allowed to remain in the cloth.

Figs. 6 and 7 represent the elevation and plan of a dyeing box on the latest and most improved construction.

a, the winch for moving the cloth through the liquor while dyeing. b, steam pipe for supplying the vessel with steam. c, c, e, the dotted part, represents the valves through which the steam enters into the vessel. d, d, d, divisions of the vessel for different pieces of cloth. e, catch for stopping or setting on the winch at pleasure. f, valve for regulating the quantity of steam admitted. Figs. 8 and 9 represent a section and elevation of the clearing boiler. Fig. 10 represents exactly the mouth of this boiler, and fig. 11 the lid or cover. On the upper edge of this cover there is fixed all round a layer of hemp (a piece of flat rope). The lid is slilt into the inside of the boiler, and by the piece of rope it attaches itself exactly to the inside. The elasticity of the steam within presses it firmly against the inside rim of the mouth, and renders it quite steam-tight.

The scarlet colour communicated to cotton by means of cochineal is far from being permanent; but if this colour is wished to be communicated to cotton, Dr Bancroft recommends to steep the cotton, previously moistened, for half an hour, in a diluted solution of muri-sulphate of tin, and then having wrung the cotton, to plunge it into water in which as much potash has been dissolved as will neutralize the acid adhering to the cotton, so that the oxide of tin may be more copiously fixed on the fibres of the cotton. The stuff being afterwards rinsed in water, may be dyed with cochineal and quercitron bark, in the proportion of four pounds of the former to two and a half or three pounds of the latter. A full bright colour is thus given to the cotton, which will bear slight washings with soap, and exposure to the air. Indeed the yellow part of the colour derived from quercitron bark will bear long boiling with soap, and will resist the action of acids.

With the aluminous mordant, as it is usually applied by calico-printers for madder reds, cotton dyed with cochineal receives a beautiful crimson colour, which will bear several washings, and resist the weather for some time. It is not, however, to be considered as a fixed colour. Dr Bancroft is of opinion that the addition of a small portion of cochineal in dyeing madder reds upon the finer cottons, would be highly advantageous to the calico-printers. By this addition the madder reds are rendered more beautiful, and the fawn colour, or brownish-yellow hue, which injures these colours, would be thus overcome.¹

Sect. II.—Of Yellow.

All the yellow dyes, as well as the red, require a mordant to fix them on the cloth; and the usual mordant employed is alumina. As in the last section, we shall in the first place give an account of the dyestuffs usually employed for giving a yellow colour to cloth, and then give a sketch of the methods employed for giving a yellow colour to wool, silk, cotton, and linen.

I.—Description of the Dyestuffs.

The principal colouring matters used in dyeing yellow are weld, fustic, catechu, annota, and quercitron. We shall give a short account of these dyestuffs in succession.

1. Weld, in French gaud or vaud, is the dried leaves and stems of the reseda luteola, a plant which grows wild in Britain, and in different European countries. Its leaves are long, narrow, and of a bright green, but the whole plant is made use of in the dyeing of yellow. There are two kinds of weld, cultivated and wild, the former of which is deemed more valuable than the latter, as it yields a much greater proportion of colouring matter. When this plant is fully ripe, it is pulled, dried, and bound up in bundles for the use of the dyer. The wild species grows higher and has a stronger stalk than that which is cultivated; by which the one may be readily distinguished from the other.

A decoction of this plant, if strong, has a brownish-yellow colour, and when diluted with water, it acquires a shade of green. The acids render this colour more pale, while alkalies, common salt, and sal ammoniac, render it deeper; and when sufficient quantities of these substances are dissolved in the decoction, a deep-yellow precipitate falls. A solution of alum or of protochloride of tin throws down a fine yellow lake; sulphate of iron occasions a black precipitate, and sulphate of copper a brownish-green precipitate.

Chevreul has discovered in weld a yellow colouring Luteolin matter, to which he has given the name of luteolin. It may be sublimed, and in that case it crystallizes in needles, which are transparent, and have a pale-yellow colour. Luteolin dissolves in water, but the solution has little colour; yet silk or woollen previously impregnated with alumina, if passed through it, acquires a fine yellow colour. It is soluble in alcohol and ether. It combines with acids, but still more readily with bases. The compound which it forms with potash has a golden-yellow colour; but when exposed to the air it assumes first a shade of green, and then passes into brown. The compounds of luteolin with the other bases are easily obtained by double decomposition.

The yellow colour communicated by weld is more permanent than that communicated by quercitron or by old fustic.

2. Fustic² is the name given by the dyers in Great Bri-

tain to the wood of the morus tinctoria, a tree which grows in the West Indies, and probably also in South America. In France it is distinguished by the name of bois jaune. The wood is yellow, as its name imports, with orange veins. Ever since the discovery of America it has been used in dyeing, as appears from a paper in the Transactions of the Royal Society, of which Sir William Petty was the author. Its price is moderate, the colour it imparts is permanent, and it readily combines with indigo, which properties give it a claim to attention as a valuable ingredient in dyeing. Before it can be employed as a dyestuff, it must be cut into chips and put into a bag, that it may not fix in, and tear the stuff, to which it is to impart its colouring matter.

When a decoction of yellow wood or fustic is made Properties very strong, the colour is of a reddish yellow, and when diluted it is of an orange yellow, which it readily yields to water. It becomes turbid by means of acids, its colour is of a pale yellow, and the greenish precipitate may be re-dissolved by alkalies. The sulphates of zinc, iron, and copper, as well as alum, throw down precipitates composed of the colouring matter and the different bases of the salts employed.

Chevreul discovered in fustic a yellow uncrystallizable Morin colouring matter, to which he has given the name of morin. It restores the colour of turmeric paper reddened by green. It is but little soluble in water, even when boiling hot. Alcohol is a better solvent of it than water, and ether still better than alcohol. When the alcoholic or ether solutions are evaporated, they deposit yellow crystals. The aqueous solution is rendered muddy by gelatine. The solutions of the fixed alkalies and alkaline earths give the aqueous solution a fine yellow colour,

¹ Philosophy of Permanent Colours, 317. ² The origin of the word fustic is not very well understood. Bancroft supposes that fustic is merely a corruption of the word fusset. When the morus tinctoria was introduced, about a couple of centuries ago, being the wood of a large tree, it was called old fustic, while the rhod cotinus, being only a shrub, was called young fustic. Rhus cotinus being now hardly used by dyers, the term fustic has been assigned to the wood of the morus tinctoria. without occasioning any precipitate. Alum causes it to assume a greenish-yellow colour. The sulphated peroxide of iron renders it green, and then throws down a precipitate. Concentrated sulphuric acid increases the intensity of the yellow colour, while nitric acid gives it a reddish shade, and renders it muddy. Boiling nitric acid converts it into oxalic acid. By combining with oxygen it seems to assume a red colour. Morin, when distilled, yields a liquid, which crystallizes as it cools, and furnishes a number of yellowish-brown needles. According to the experiments of George, boiling water extracts from fustic 0.15, and alcohol 0.09 of matter; and the wood is composed of:

| Constituents | Quantity | |-------------|----------| | Lignin | 74 | | Morin | 9.1 | | Tannin | 4 | | Gum | 2 | | Resin | 9 |

3. Catechu, or *terra japonica*, comes from the East Indies, and is the inspissated decoction of certain plants containing tannin, but principally of the *areka nut*, the wood of *mimosa catechu*, the leaves of the *nauclea catechu*. Areka nuts, cut into small pieces, are sprinkled in an earthen vessel with water holding saltpetre in solution. A portion of the bark of kantai-babela (a species of mimosa) is added. The vessel is closed by a lid luted down with clay, that the temperature may be the higher. After an ebullition of two hours, the fire is gradually diminished during five or six hours. When the vessel is cold the areka nuts are taken out, and the decoction is evaporated down to the consistency of a syrup. It is then kneaded into small balls, and left to dry in the shade.

The principal constituents of catechu are tannin and extractive. The former may be thrown down by gelatine, the latter remains in solution. It has a reddish-brown colour and a sweetish taste. In India catechu is employed in dyeing and calico-printing. The colours which it gives are very various, depending upon the nature of the mordants employed along with it; but they are all very fixed. With verdigris and sal ammoniac the colour is brown; with protocloride of tin yellow; with perchloride of tin a brown, or, if nitrate of copper be added, a deep bronze; with nitrate of alumina a copper red; with nitrate of iron a deep brownish gray.

We are not aware that catechu is employed in this country, either by the dyers or calico-printers; but it is entitled to their attention, both on account of its cheapness, and the permanency and variety of the colours which it gives.

4. Anotta, in French *rocou*, is a species of paste of a red colour, obtained from the berries of the *bixa orellana*, Lin. which is a native of America. The anotta of commerce is imported from America to Europe in cakes of two or three pounds weight, where it is prepared from the seeds of the tree mentioned above; but the Americans are said to be in possession of a species of anotta superior to that which they export, both for the brilliancy and permanency of the colour it imparts. They bruise the seeds with their hands moistened with oil, separating with a knife the paste as it is formed, and drying it in the sun; but the seeds are pounded with water when designed for sale, and allowed to undergo the process of fermentation.

According to John, the cakes of anotta are composed of twenty-eight parts of resin mixed with colouring matter, twenty parts of coloured extractive, twenty-six of gum, and twenty of lignin, mixed with an acid and an aromatic substance.

The colouring matter of anotta is but little soluble in water, though it communicates a yellow colour to that liquid. It is more soluble in alcohol, and tinges it orange. Ether dissolves it still better, and assumes also an orange colour. We obtain the colouring matter in a sufficiently pure state by evaporating the alcoholic solution to dryness, treating the residue with ether, and finally distilling off the ether. It is a reddish-brown substance, heavier than water, soft and adhesive. Even when exposed to a very low temperature, it does not become brittle. When heated it melts, and when sufficiently heated in an open vessel it takes fire and burns like a resin.

We may likewise obtain the colouring matter of anotta by digesting it in a caustic alkaline solution, and then saturating the alkali by an acid. The colouring matter precipitates in orange flocks. Concentrated sulphuric acid gives anotta an indigo-blue colour; but in contact with air this colour soon passes into green, and then into violet brown. Cold nitric acid does not alter the colour of anotta but if the quantity of acid be small, the mixture assumes the consistence of a syrup, and detonates when slightly heated, leaving charcoal. Anotta gives an orange-red colour to oils, both fixed and volatile.

According to Chevreul, anotta contains two different colouring matters, the one yellow and the other red. The yellow colouring matter is soluble in water and alcohol, and slightly in ether; the red colouring matter is scarcely soluble in water, but it dissolves in alcohol and ether, communicating to these liquids an orange-red colour.

Anotta yields an orange precipitate with a solution of alum, and the sulphates of copper and iron produce effects of nearly a similar nature. With a solution of tin the precipitate is of a lemon colour, and slowly deposited.

It is employed both for dyeing silk and cotton, but the colours which it yields have little permanency.

5. Quercitron bark.—Quercitron, as it is denominated by Dr Bancroft, is the *quercus nigra* of Linnaeus, and is a large tree which grows spontaneously in North America. The bark of it yields a considerable quantity of colouring matter, which was first discovered by Dr Bancroft in the year 1784, in whom the use and application of it in dyeing were exclusively vested for a certain term of years by virtue of an act of parliament. To prepare it for use, the epidermis is taken off and pounded in a mill, the result of which process is a number of filaments and a fine light powder; but as these do not contain equal quantities of colouring matter, it will be proper to employ them in their natural proportions.

Quercitron bark contains a good deal of tannin, and a yellow colouring matter capable of being extracted by water. The aqueous solution, when evaporated to dryness, leaves a quantity of extract, amounting to eight per cent. of the weight of the bark employed. The tannin is that variety which forms a green precipitate with oxide of iron. Its presence is injurious to the beauty of the yellow colour, because it is precipitated by the same re-agents as the colouring matter itself, and of course communicates to it a shade of brown. To free the colouring matter from tannin, ox bladder steeped in water, and deprived of everything soluble in cold water, is introduced into the quercitron infusion. With this substance the tannin gradually unites, and thus is removed from the solution. It may be thrown down also by a solution of gelatine.

When the infusion of quercitron is gently concentrated, the colouring matter is deposited in crystals, which have a pearly lustre as long as they continue suspended in the liquid. To this colouring matter Chevreul has given the name of *quercitria*. It restores the yellow colour of turmeric paper reddened by an alkali. It is but little soluble in ether, more soluble in alcohol, and still more soluble in water. The aqueous solution is tinged orange by al- kalies. The acetates of lead and copper, and the protoc- chloride of tin, throw it down in yellow flocks. The sul- phated peroxide of iron gives it an olive-green colour; and then precipitates it. Sulphuric acid dissolves quercitrin, the solution is orange with a shade of green, and is ren- dered muddy when mixed with water. When quercitrin is subjected to distillation, it yields, among other products, a liquid which speedily deposits yellow crystals possess- ing the characters of quercitrin.

Besides the substances already mentioned as employed in the dyeing of yellow, we may add saw-wort to the num- ber (Serratula tinctoria, Lin.), a plant which yields a co- louring matter nearly similar to that of weld, and may of consequence be used as a proper substitute. Dyers' broom (Gemula tinctoria) produces a yellow of very indifferent nature, and is therefore only employed in dyeing stuffs of the coarsest kind. Tumeric (Curcuma longa) is a native production both of the East and West Indies, and yields a more copious quantity of colouring matter than any other yellow dyestuff; but it will probably never be of any essential service in dyeing yellow, as no mordant has yet been discovered capable of giving permanency to its colour.

Chamomile (Anthemis tinctoria) yields a faint yellow colour, the hue of which is not unpleasant, but is far from being durable, and even mordants are not capable of fixing it. Sulphate of lime, tartar, and alum, bid fairest for success.

Fenugreek (Trigonella foenum-graecum) yields seeds which, when ground, communicate to stuffs a pale yellow of to- lerable durability; and the best mordants are found to be alum and muriate of soda, or common salt. American hic- cory (Juglans alba) is a tree, the bark of which yields a colouring matter in every respect resembling that of the Quercus nigra, but in quantity greatly inferior. French berries (Rhamnus infectarius) produce a tolerable yellow colour, but it is by no means permanent. When used in the process of dyeing, they are to be employed in the same manner as weld. According to Scheffer, a fine yel- low colour may be imparted to silk, thread, and wool, by means of the leaves of the willow; but Bergman informs us that only the leaves of the sweet willow (Salix pentan- dra) are proper for producing a permanent colour, as a few weeks exposure to the sun extracts that which is pro- duced by the colouring matter from the leaves of the com- mon willow.

In Switzerland and in England the seeds of purple tre- foil are sometimes employed in the art of dyeing, on which Vogler made a number of experiments, in order to ascer- tain what colours they would produce; and he found that a fine deep yellow was afforded by a bath made of a solu- tion of these seeds with potash; that sulphuric acid yield- ed a light yellow, and sulphate of copper or blue vitriol a yellow inclining to green. M. Dize informs us that the seeds of trefoil impart to wool a beautiful orange, and to silk a greenish yellow; and that while aluming is neces- sary in the process of dyeing with the seeds of trefoil, a solution of tin cannot be employed.

Many other vegetable substances are occasionally em- ployed in dyeing yellow, but it seems useless to enu- merate them. Saffron and turmeric yield exceedingly beautiful but fugitive yellows. The colouring matter of saffron (Crocus sativus) is extremely rich; it has been sub- jected to a chemical examination, and distinguished by the name of polychroite by Bouillon La Grange and Vog- ler, to whom we are indebted for the first examination of it.

The finest and most fixed of all the yellows on cotton is chromate of lead. It is employed abundantly by the calico-printers, but scarcely by the dyers in general. On that account we think it better to reserve it till we come to that part of this article in which we propose to describe the processes followed by the calico-printers.

II.—Of the Processes for dyeing Wool Yellow.

In dyeing woollen stuffs with weld, the mordants em- ployed are alum and tartar, and by their means a pure, permanent yellow is obtained. The boiling is to be con- ducted in the usual way; and, according to Hellot, four ounces of alum to one ounce of tartar are to be employed. Other dyers, however, employ half as much tartar as alum. The colour is rendered paler, but more lively, by means of the tartar.

The bath is prepared by boiling the plant inclosed in a Prepara- thin linen bag, and keeping it from rising by means of a thin cross. Some boil it till it sinks to the bottom of the vessel; while others, after it is boiled, take it out and throw it away. From three to four pounds of weld, and sometimes less, are allowed for every pound of stuff; but the quantity must be regulated by the intensity of the shade desired. Some dyers add a small quantity of quick- lime and ashes, which are found to promote the extrac- tion of the colouring matter. These substances at the same time heighten the colour, but render it less suscep- tible of resisting the action of acids.

With other additions, and different management, differ- ent shades may be obtained. Thus lighter shades are produced by dyeing after deeper ones, adding water at each dipping, and keeping the bath at the boiling tempera- ture. These shades, however, are less lively than when fresh baths are employed, with a suitable proportion of weld. The addition of common salt or sulphate of lime to the weld bath communicates a richer and deeper co- lour. With alum it is paler and more lively, with tartar still paler, and with sulphate of iron the shade inclines to brown. According to Scheffer, by boiling the stuff two hours, with one fourth of its weight of a solution of tin, and the same proportion of tartar, and then washing and boiling it with an equal weight of weld, a fine yellow is produced; but if the stuff be in the state of cloth, its in- ternal texture is not penetrated. Poerner recommends a similar preparation as for dyeing scarlet, and by these means the colour is brighter, more permanent, and lighter.

Dr Bancroft recommends the quercitron bark as one of the cheapest and best substances for dyeing wool yellow, citron bark. The following is the simple process which he has propos- ed for its application. The bark is to be boiled up with about its weight, or one third more, of alum, in a suitable proportion of water, for about ten minutes. The stuff pre- viously scoured is then to be immersed in the bath, tak- ing care to give the higher colours first, and afterwards the paler straw colours. By this cheap and expeditious process, colours which are not wanted to be of a full or bright yellow may be obtained. The colour may be con- siderably heightened by passing the unrisen stuff a few times through hot water, to which a little clean powdered chalk, in the proportion of about a pound and a half for each 100 lbs. of stuff, has been previously added. The bark, when used in dyeing, being first reduced to powder, should be tied up in a thin linen bag, and suspended in the liquor, so that it may be occasionally moved through it, to diffuse the colouring matter more equally.

But although the above method possesses the advan- tages of cheapness and expedition, and is fully sufficient permanent for communicating pale yellows; to obtain fuller and more colours. permanent colours, the common mode of preparation, by previously applying the aluminous mordant, ought to be preferred. The stuff, therefore, should be boiled for about one hour or one hour and a quarter, with one sixth or one eighth of its weight of alum dissolved in a proper pro- portion of water. The stuff is then to be immersed, without being rinsed, into the dyeing bath, with clean hot water, and about the same quantity of powdered bark tied up in a bag as that of the alum employed in the preparation. The stuff is then to be turned as usual through the boiling liquor, until the colour appears to have acquired sufficient intensity. One pound of clean powdered chalk for every 100 lbs. of stuff is then to be mixed with the dyeing bath, and the operation continued for eight or ten minutes longer. This addition of the chalk raises and brightens the colour.

**Orange Yellow.**—To communicate a beautiful orange yellow to woollen stuffs, ten lbs. of quercitron bark, tied up in a bag, for every 100 lbs. of stuff, are to be put into the bath with hot water. At the end of six or eight minutes, an equal weight of murio-sulphate of tin is to be added, and the mixture well stirred for two or three minutes. The cloth, previously scoured, and completely wetted, is then immersed in the dyeing liquor, and briskly turned for a few minutes. By this process the colouring matter fixes on the cloth so quickly and equally, that after the liquor begins to boil, the highest yellow may be produced in less than fifteen minutes.

High shades of yellow, somewhat similar to those obtained from quercitron bark by the above process, are frequently given with young fustic (*Rhus cotinus*, Linn.), and dyers' spirit, or nitro-muriate of tin; but this colour is much less beautiful and permanent, while it is more expensive, than what is obtained from the bark.

**Bright Golden Yellow.**—This colour is produced by employing ten pounds of bark for every 100 pounds of cloth, the bark being first boiled a few minutes, and then adding seven or eight pounds of murio-sulphate of tin, with about five pounds of alum. The cloth is to be dyed in the same manner as in the process for the orange yellow.

Bright yellows of less body are produced by employing a smaller proportion of bark, as well as by diminishing the quantity of murio-sulphate of tin and alum. And indeed every variety of shade of pure bright yellow may be given by varying the proportions of the ingredients.

To produce the lively delicate green shade, which, for certain purposes, is greatly admired, the addition of tartar, with the other ingredients, only is necessary, and the tartar must be added in different proportions, according to the shade which is wanted. For a full bright yellow, delicately inclining to the greenish tinge, it will be proper to employ eight pounds of bark, six of murio-sulphate of tin, with six of alum, and four of tartar. An additional proportion of alum and tartar renders the yellow more delicate, and inclines it more to the green shade; but when this lively green shade is wanted in the greatest perfection, the ingredients must be used in equal proportions.

The delicate green lemon yellows are seldom required to have much fulness or body. Ten pounds of bark, therefore, with an equal quantity of the other ingredients, are sufficient to dye three or four hundred pounds of stuffs.

To produce the exquisitely delicate and beautiful pale green shades, the surest method, Dr Bancroft observes, is to boil the bark with a small proportion of water, in a separate tin vessel, for six or eight minutes, and then to add the murio-sulphate of tin, alum, and tartar, and to boil them together for about fifteen minutes. A small quantity of this yellow liquor is then to be put into a dyeing vessel which has been previously supplied with water sufficiently heated. The mixture being properly stirred, the dyeing process is to be conducted in the usual way, and the yellow liquor, as it is wanted, gradually added from the first vessel. In this way the most delicate shades of lively green lemon yellows are dyed with ease and certainty. Weld is the only dyestuff from which similar shades of colour can be obtained; but it is four times more expensive. The yellows dyed from quercitron bark, Dr Bancroft adds, with murio-sulphate of tin and alum as mordants, do not exceed the expense of one penny for each pound of stuff, besides a considerable saving of time, labour, and fuel.

A greenish shade may also be produced without tartar, by substituting verdigris dissolved in vinegar, along with the bark; but it is neither so permanent, nor so bright and delicate, as that produced by means of tartar. Sulphate of indigo also, in very small proportion, communicates a similar shade when it is employed with the bark, murio-sulphate of tin, and alum; but it is apt to take unequally on the stuff, and besides, in the language of the dyers, the colour has a tendency to cast or fly in the finishing.

Small proportions of cochineal, employed along with the bark and other ingredients, raise the colour to a beautiful orange, and even to an aurora. Madder may also be employed with the same view, for it heightens the yellow obtained from quercitron bark, although the colour thus obtained is inferior in beauty to that from cochineal. The madder may also be employed with weld for the same purpose.

The colours obtained from quercitron bark, by the processes which we have now described, are very durable. They resist the action of the air, of soap, and of acids. It is by the effects of alum, but especially of tartar, that these colours become so fixed as to remain permanent by exposure to the air. It is observed of the highest yellows, even when they approach to the orange, and which are best dyed either with muriate or murio-sulphate of tin and bark, that although they resist the action of soap and acids, they are apt to lose their lustre and become brown by the effect of the sun and air; but this also happens to yellows dyed with nitro-muriate of tin, both with the bark and with weld, but in a still greater degree with other yellow vegetable colouring matters. In some of these this defect is less easily obviated by alum and tartar, than it is in the yellow obtained from weld and quercitron bark.

**III.—Of the Processes for dyeing Silk Yellows.**

To dye silk a plain yellow colour, the only ingredient which was formerly employed was weld. The following is the process. The silk being previously scoured in the proportion of twenty pounds of soap to the hundred of stuff, and then alummed, and washed after the alumming, or, as it is called, refreshed, the bath is prepared with two pounds of weld for every pound of silk; and having boiled for fifteen minutes, it is to be passed into a vat through a sieve or cloth. When the temperature is such as the hand can bear, the silk is introduced and turned until it has acquired a uniform colour. While this operation is going on, the weld is to be boiled a second time in fresh water; one half of the first bath is taken out, and its place supplied with a fresh decoction. The temperature of the fresh bath may be a little higher than the former; but it is necessary to guard against too great a degree of heat, that the colouring matter already fixed may not be dissolved. The stuff is to be turned as before, and afterwards taken out of the bath. A quantity of soda is to be dissolved in a part of the second decoction, and a larger or smaller proportion of this solution is to be added to the

---

1 Bancroft, 330. 2 Ibid. 333. 3 Ibid. 335. 4 Ibid. 334. bath, according to the intensity of the shade required. When the silk has been turned a few times, a skin is wrung out, that it may be examined whether the colour be sufficiently full, and have the proper golden shade. To render the colour deeper, and to give it the gold cast, an addition of the alkaline solution is to be made to the bath, and to be repeated till the shade has acquired sufficient intensity. The alkaline solution may also be added along with the second decoction of the weld, observing the precaution that the temperature of the bath be never too great.

To produce other shades of yellow, having more of a gold or jonquille colour, a quantity of anota, proportioned to the shade required, is to be added to the bath along with the alkali. Lighter shades of yellow, such as pale lemon or Canary bird colour, are obtained by previously whitening the silk, and regulating the proportion of ingredients in the bath by the shade required. To communicate a yellow having a tinge of green, a little indigo is added to the bath, if the silk has not been previously azured. To prevent the intensity of the shade from being too great, the silk may be more slightly alumed than usual.

But, according to Dr Bancroft, the different shades of yellow obtained from weld may be given to silk with equal facility and beauty, and at a cheaper rate, by employing quercitron bark as a substitute. A quantity of bark powdered and enclosed in a bag, in proportion to the shade of colour wanted, as from one to two pounds for every twelve pounds of silk, is put into the dyeing vat while the water is cold. Heat is then applied; and when it has become rather more than blood warm, or of the temperature of 100°, the silk, having previously undergone the aluming process, is to be immersed and dyed in the usual way. If a deep shade is wanted, a small quantity of chalk or pearl-ashes may be added towards the end of the operation. To produce a more lively yellow, a small proportion of murio-sulphate of tin may be employed; but it should be cautiously used, as it is apt to diminish the lustre of the silk. To produce such a shade, the proportions of the ingredients may be four pounds of bark, three of alum, and two of murio-sulphate of tin. These are to be boiled with a proper quantity of water for ten or fifteen minutes; and the temperature of the liquid being so much reduced as the hand can bear it, the silk is immersed and dyed as usual, till it has acquired the proper colour. Care should be taken to keep the liquor constantly agitated, that the colouring matter may be equally diffused.

To dye silk of an aurora or orange colour, after being properly scoured, it may be immersed in an alkaline solution of anota, the strength of which is to be regulated by the shade required; and the temperature of the bath should be between tepid and boiling water. When the desired shade has been obtained, the silks are to be washed and twice beetleed, to free them from the superfluous colouring matter, which would injure the beauty of the colour. When raw silk is to be dyed, that which is naturally white should be selected, and the bath should be nearly cold; for otherwise the alkali, by dissolving the gum of the silk, destroys its elasticity. Silk is dyed of an orange shade with anota; but the stuffs must be reddened with vinegar, alum, or lemon juice. The acid, by saturating the alkali employed to dissolve the anota, destroys the yellow shade produced by the alkali, and restores its natural colour, which inclines to a red. But although beautiful colours are obtained by this process, they do not possess any great degree of permanency.

Several kinds of mushrooms afford lively and durable yellow dyes. A bright shining dye of this description has been extracted from the *boletus hirsutus*, which commonly grows on walnut and apple trees. The colouring matter is contained both in the tubular part, and also in the parenchyma of the body of the mushroom. To extract the colouring matter, it is pounded in a mortar, and the liquor which is thus obtained is boiled for a quarter of an hour in water. An ounce of liquor is sufficient to communicate colouring matter to six pounds of water. After the liquor has been strained, the stuff to be dyed is immersed in it, and boiled for fifteen minutes. When silk is subjected to this process, after being dyed, it is made to pass through a bath of soft soap, by which it acquires a shining golden yellow colour, which has a near resemblance to the yellow of the silk employed to imitate embroidery in gold. This has been hitherto brought from China, and bears a very high price, the method of dyeing it being unknown in Europe. All kinds of stuff receive this colour; but it is less bright on linen and cotton, and seems to have the strongest affinity for silk. The use of mordants, it is supposed, would modify and improve it greatly.

IV.—Of the Processes for dyeing Cotton and Linen Yellow.

The process which has been usually followed in dyeing cotton and linen yellow, is by scouring it in a bath prepared in a ley with the ashes of green wood. It is afterwards washed, dried, and alumed, with one fourth of its weight of alum. After twenty-four hours it is taken out of the aluming and dried, but without being washed. The cotton is then dyed in a weld bath, in the proportion of one pound and a quarter of weld for each pound of cotton, and turned in the bath till it has acquired the proper colour. After being taken out of the bath, it is soaked for an hour and a half in a solution of blue vitriol (sulphate of copper), in the proportion of one fourth of the weight of the cotton, and then immersed, without washing, for nearly an hour in a boiling solution of white soap, after which it is well washed and dried.

A deeper yellow is communicated to cotton by omitting the process of aluming, and employing two pounds of yellow, and a half of weld for each pound of cotton. To this is added a dram of verdigris, mixed with part of the bath. The cotton is then to be dipped and worked till the colour become uniform. It is then taken out of the bath, that a little solution of soda may be added, after which it is returned and kept for fifteen minutes. It is then wrung out and dried.

Other shades of yellow may be obtained by varying the proportion of ingredients. Thus a lemon colour is dyed shades by using only one pound of weld for every pound of cotton, and by diminishing the proportion of verdigris, or using alum as a substitute.

But a better method, as it affords more permanent and more beautiful colours, and at a smaller expense, is recommended by Dr Bancroft. This is by the use of quercitron permanent bark, and the calico-printers' aluminous mordant, or the sugar of lead. The following is the process which he proposes to employ for producing bright and durable yellow colours. One pound of sugar of lead and three pounds of alum are to be dissolved in a sufficient quantity of warm water. The cotton or linen, after being properly rinsed, is to be soaked in this mixture, heated to the temperature of 100°, for two hours. It is then taken out, moderately pressed over a vessel, to prevent the waste of the alumious liquor. It is then dried in a stove heat, and after being again soaked in the aluminous solution, it is wrung.

---

1 Bancroft, 345. 2 Philosophical Magazine, vol. 100. 3 Berthollet, ii. 267. out and dried a second time. Without being rinsed, it is to be barely wetted with lime water, and afterwards dried; and if a full, bright, and durable yellow is wanted, it may be necessary to soak the stuff in the diluted aluminoous mordant, and, after drying, to wet it a second time with lime water. After it has been soaked for the last time, it should be well rinsed in clean water, to separate the loose particles of the mordant, which might injure the application of the colouring matter. By the use of the lime-water, a greater proportion of alumina combines with the stuff, besides the addition of a certain proportion of lime.

In the preparation of the dyeing bath, from twelve to eighteen pounds of powdered quercitron bark are inclosed in a bag; for every hundred pounds of the stuff, varying the proportion according to the intensity of the shade desired. The bark is put into the water while it is cold; and immediately after, the stuff is immersed and agitated or turned for an hour or an hour and a half, during which the water should be gradually heated, and the temperature raised to about 120°. At the end of this time the heat is increased, and the dyeing liquor brought to a boiling temperature; but at this temperature the stuff must remain in it only for a few minutes, because otherwise the yellow assumes a brownish shade. The stuff having thus acquired a sufficient colour, is taken out, rinsed, and dried.

Dr Bancroft observes, that when the aluminoous mordant is employed without the addition of water, one soaking only, and an immersion in lime water, may be sufficient; but he thinks that greater advantage is derived from the application of a more diluted mordant at two different times, or even by the immersion of the stuff a greater number of times, alternately in the diluted aluminoous mordant, and lime water, and drying it after each immersion. By this treatment he found that the colour always acquired more body and durability.

Chaptal has proposed a process for communicating to cotton a nankeen yellow, which, at the same time that it affords a durable colour, has the advantage of being cheap and simple. When cotton is immersed in a solution of any salt of iron, it has so strong an affinity for the oxide, that it decomposes the salt, combines with the iron, and assumes a yellow colour. The process recommended by Chaptal is the following: The cotton to be dyed is put into a cold solution of copperas (sulphate of iron), of the specific gravity 1·02. It is afterwards wrung out, and immediately immersed in a ley of potash of the specific gravity 1·01. This ley must have been previously saturated with a solution of alum. When the stuff has been kept for four or five hours in this bath, it may be taken out, washed, and dried. By varying the proportion of sulphate of iron, every variety of shade of nankeen yellow may be obtained.

We shall lay before our readers another process for dyeing nankeen colour, which is proposed and followed by Mr Brewer, a practical dyer. It is as follows:

"Mix as much sheep's dung in clear water as will make it appear of the colour of grass; and dissolve in clear water one pound of best white soap for every ten pounds of cotton yarn, or in that proportion for a greater or lesser quantity.

"Observe:—The tubs, boards, and poles, that are used in the following preparations must be made of deal; the boiling pan of either iron or copper.

First operation.—Pour the soap liquor prepared as above into the boiling pan; strain the dung liquor through a sieve; add as much thereof to the soap liquor in the pan as will be sufficient to boil the yarn intended to be dyed, for five hours. When the liquors are well mixed in the pan, enter the yarn, light the fire under the pan, and bring the liquor to boil in about two hours, observing to increase the heat regularly during that period. Continue it boiling for three hours; then take the yarn out of the pan, wash it, wring it, and hang it in a shed on poles to dry. When dry, take it into a stove or other room where there is a fire; let it hang there until it be thoroughly dry.

N. B.—The cotton yarn, when in the shed, should not be exposed either to the rain or sun. If it is, it will be unequally coloured when dyed.

Second operation.—In this operation use only one half of the soap that was used in the last, and as much dung liquor (strained as before directed) as will be sufficient to cover the cotton yarn, when in the pan, about two inches. When these liquors are well mixed in the pan, enter the yarn, light the fire, and bring the liquor to boil in about one hour; then take the yarn out, wring it out without washing, and hang it to dry, as in the former operation.

Third operation.—This operation the same as the second in every respect.

Fourth operation.—For every ten pounds of yarn make a clear ley from half a pound of pot or pearl ashes. Pour the ley into the boiling pan, and add as much clear water as will be sufficient to boil the yarn for two hours; then enter the yarn, light the fire, and bring it to boil in about an hour. Continue it boiling about an hour, then take the yarn out, wash it very well in clear water, wring it, and hang it to dry, as in former operations.

N. B.—This operation is to cleanse the yarn from any oleaginous matter that may remain in it after boiling in the soap and dung liquors.

Fifth operation.—To every gallon of iron liquor add half a pound of ruddle or red chalk (the last the best) well pulverized.

"Mix them well together, and let the liquor stand four hours, in order that the heavy particles may subside; then pour the clear liquor into the boiling-pan, and bring it to such a degree of heat as a person can well bear his hand in; divide the yarn into small parcels, about five hanks in each; soak each parcel or handful very well in the above liquor, wring it, and lay it down on a clean deal board. When all the yarn is handed through the liquor, the last handful must be taken up and soaked in the liquor a second time, and every other handful in succession, till the whole is gone through; then lay the yarn down in a tub, wherein there must be put a sufficient quantity of ley, made from pot or pearl ashes, as will cover it about six inches. Let it lie in this state about two hours, then hang it over in the ley, wring it, and lay it down on a clean board. If it does not appear sufficiently deep in colour, this operation must be repeated till it has acquired a sufficient degree of darkness of colour. This done, it must be hung to dry, as in former operations.

N. B.—Any degree of red or yellow hue may be given to the yarn, by increasing or diminishing the quantity of ruddle or red chalk.

Sixth operation.—For every ten pounds of yarn make a ley from half a pound of pot or pearl ashes; pour the clear ley into the boiling pan; add a sufficient quantity of water thereto, that will cover the yarn about four inches; light the fire, and enter the yarn when the liquor is a little warm; observe to keep it constantly under the liquor for two hours; increase the heat regularly till it come to a scald; then take the yarn out, wash it, and hang it to dry, as in former operations.

Iron liquor is what the linen-printers use. Seventh operation.—"Make a sour liquor of oil of vitriol and water. The degree of acidity may be a little less than the juice of lemons; lay the yarn in it for about an hour, then take it out, wash it very well, and wring it; give it a second washing and wringing, and lay it upon a board.

N.B.—This operation is to dissolve the metallic particles, and remove the ferruginous matter that remains on the surface of the thread after the fifth operation.

Eighth operation.—"For every ten pounds of yarn dissolve one pound of best white soap in clear water, and add as much water to this liquor in your boiling-pan as will be sufficient to boil the yarn for two hours. When these liquors are well mixed, light the fire, enter the yarn, and bring the liquor to boil in about an hour. Continue it boiling slowly an hour; take it out, wash it in clear water very well, and hang it to dry, as in former operations. When dry, it is ready for the weaver.

N.B.—It appears to me, from experiments that I have made, that less than four operations in the preparation of the yarn will not be sufficient to cleanse the pores of the fibres of the cotton, and render the colour permanent."

A method of giving a very fixed yellow to cotton and linen is practised in the East. It is precisely similar to the plan followed in dyeing Turkey red. The cloth is first impregnated with the oleaginous soap. It is then passed through a decoction of nutgalls, or of some substance containing tannin. The alumious mordant is then applied. After all these preliminary steps have been accomplished, the cloth is dyed in the usual way with quercitron bark. These complicated processes being precisely similar to those followed by the Turkey-red dyers, we refer the reader for particulars to the fourth division of the first section of the present chapter.

Such processes, however, are unnecessary in this country, because as permanent and beautiful a colour can be given at once to cotton by impregnating it with acetate or nitrate of lead, and then passing the cloth through a solution of bichromate of potash.

Sect. III.—Of Blue.

We shall follow the same method in giving an account of the blue dye, as we did when giving an account of the red and yellow dyes; that is to say, we shall first notice the dyestuffs, and then describe the processes followed by the dyers.

I.—Description of the Dyestuffs.

The only dyestuff used for giving a blue colour to cloth is indigo, a blue pigment obtained from various species of plants. The most common plant yielding indigo is the Indigofera, of which there are three species, the tinctoria, the dispersa, and the argentea. The serium tinctorium, or rose bay, a tree which is a native of India, also yields it. The method of procuring indigo from these plants, the nature and properties of indigo, and its composition, have been detailed in the article Chemistry in this Encyclopedia, to which therefore we refer the reader.

Mr Crum has shown that the atomic constituents of indigo are,

| Atoms | Element | |-------|---------| | 16 | Carbon | | 4 | Hydrogen| | 1 | Azote | | 2 | Oxygen |

Indigo in its perfect state is insoluble in water and alcohol, and has not the property of combining with bases. But when deprived of one atom of oxygen, it assumes a yellow colour, and in that state is capable of combining with lime or potash, and doubtless with other bases, and of forming with them compounds which dissolve in water. When cloth to be dyed is dipt into the indigo vat, rendered soluble by being deprived of an atom of oxygen, and united to a base, it comes out stained yellow. But the basis of the indigo begins immediately to attract oxygen from the atmosphere, and to resume its blue colour. This causes the cloth speedily to become green by the mixture of yellow and blue, and finally to assume a deep-blue colour. No mordant is necessary, as there is a strong affinity between indigo and the fibres of the cloth.

When indigo is digested in concentrated sulphuric acid Cerulin, it undergoes a remarkable change, being converted into a peculiar blue substance, with which the Saxon blue is dyed. To this substance Mr Crum, to whom we are indebted for the first accurate examination of it, has given the name of cerulin. Mr Crum has shown that it is a compound of one integrant particle of indigo, and four integrant particles of water.

The mixture of cerulin with sulphuric acid is semifluid, which requires a considerable quantity of water to dissolve it. When potash is added to this solution, a deep-blue precipitate falls, which is a compound of sulphate of potash and cerulin. To this compound Mr Crum has given the name of cerulio-sulphate of potash. All the neutral salts have the property of combining with cerulin, and of precipitating it from its aqueous solution.

Mr Crum discovered that if the action of sulphuric acid on indigo be stopped at a certain point, a new substance is formed, different from cerulin. To this new substance he gave the name of phenicin. It may be obtained by the following process: Digest indigo in sulphuric acid diluted with thrice its weight of water. By this process the indigo is deprived of the greater part of its impurities. Mix one part of this purified indigo with seven or eight parts of concentrated sulphuric acid in a stoppered phial, and agitate the mixture occasionally till it becomes of a bottle-green colour. Then mix it with a large quantity of distilled water, and throw it upon a filter. By continuing to wash the filter, the liquid, which at first passes through colourless, becomes more and more blue, and after some time all the indigo which has been changed passes through. The colourless washings must be thrown away. The blue liquid contains the phenicin in solution, which on the addition of chloride of potassium precipitates a most beautiful reddish-purple colour, exactly similar to the colour of the vapour of indigo. Its solution is of a fine blue colour like cerulin, but when a neutral salt is added it is precipitated of a fine purple colour. Hence the origin of the term phenicin. Mr Crum has shown that it is a compound of one integrant particle of indigo and two integrant particles of water.

Indigo is not confined to plants growing within the torrid zone. The isatis tinctoria and isatis lucidiana, plants which are cultivated in England and France, yield, when treated in the same way with the leaves of the indigofera, a little indigo; but the quantity is too small to make it worth while to employ these plants for the preparation of this valuable dyestuff. But those plants under the names of pastel or woad were formerly employed for dyeing blue in all parts of Europe; and it was to prevent any supposed injury to the cultivators of woad that the em-

---

1 Edinburgh Magazine, xxii. 2 From φαντά, purple.

Simple Colours.

The employment of indigo in dyeing was prohibited in Queen Elizabeth's time in England. The limitations of the use of indigo in France and Saxony were owing to the same cause. So little at that time were the first principles of political economy understood by the rulers of the different kingdoms of Europe.

Woad is still used by the dyers in some of their processes, but merely for the purpose of de-oxidizing indigo, and thus rendering it soluble in water.

II.—Methods of dyeing Wool Blue.

The preparation for dyeing blue is made in a large wooden vessel or vat, which should be so constructed as to retain the heat, which is a matter of considerable importance in the process. The vat is therefore set up in a separate place from the coppers, and is sunk so far in the ground as to be only breast-high above it. Before the introduction of indigo, blue was dyed with woad, which furnished a permanent but not a deep colour; but a very rich blue is obtained by mixing indigo with the woad, and these are almost the only substances which are now employed for dyeing woollen stuffs. The proportions of these substances are varied by different dyers, and according to the shade which is required. The following is the account of the preparation of a vat, as it is given by Quatremere. Into a vat of about seven and a half feet deep, and five and a half in diameter, are thrown two balls of pastel or woad, which are previously broken, and together amount to about 400 pounds weight; thirty pounds of weld are boiled in a copper for three hours in a sufficient quantity of water to fill the vat. To this decoction are added twenty pounds of madder and a basket full of bran. The boiling is then continued half an hour longer. This bath is cooled with twenty buckets of water, and after it is settled, and the weld taken out, it is poured into the vat, which must be stirred with a rake all the time that it is running in, and for fifteen minutes longer. The vat is then covered up very hot, and allowed to stand for six hours, when it is uncovered, and raked again for thirty minutes. The same operation must be repeated every three hours. When the appearance of blue streaks is perceived on the surface of the vat, eight or nine pounds of quicklime are added; the colour then becomes of a deeper blue, and the vat exhales more pungent vapours. Immediately after the lime, or along with it, the indigo, which has been previously ground in a mill, with the smallest possible quantity of water, is put into the vat. The quantity is to be regulated by the intensity of the shade required. From ten to thirty pounds may be put into a vat such as we have now described. If on striking the vat with a rake a fine blue scum arises, no other previous preparation is required than to stir it with the rake twice in the space of six hours, to mix the ingredients completely. Great care should be taken not to expose the vat to the air, except during the time of stirring it. When that operation is finished, it is covered with a wooden lid, on which are spread thick cloths, to retain the heat as much as possible; but after all these precautions, at the end of eight or ten days it is greatly diminished, and is at last entirely dissipated, so that the liquor must be again heated, by pouring the greater part of the liquor of the vat into a copper under which a large fire is made. When the liquor has acquired a sufficient temperature, it is returned into the vat, and carefully covered up.

Vats of this description are sometimes liable to accidents. A vat is said to be repelled when, having previously afforded fine shades of blue, it appears black, without any blue streaks; and if it be stirred, the black colour becomes deeper; the vat at the same time exhales, instead of a sweetish smell, a pungent odour; and the stuff dyed in a vat in this state comes out of a dirty gray colour. These effects are ascribed to an excess of lime.

Different means are employed to recover a repelled vat. Some are satisfied with merely reheating it, while others add tartar, bran, urine, or madder. Hellot recommends bran and madder as the best remedy. If the excess of lime be not very great, it is sufficient to leave it at rest five or six hours, putting in a quantity of bran and three or four pounds of madder, which are to be sprinkled on the surface, and then it is to be covered up, and after a certain interval to be tried again. But if the vat has been so far repelled as to afford a blue only when it is cold, it must be left at rest to recover, and sometimes must remain whole days without being stirred with the rake. When it begins to afford a tolerable pattern, the bath must be reheated. In general this revives the fermentation. The addition of bran or madder, or a basket or two of fresh woad, produces the same effect.

This vat sometimes runs into the putrefactive process. When this happens, the colour of the vat becomes reddish, the paste rises from the bottom, and a fetid smell is exhaled. This accident is owing to a deficiency of lime, and it must be corrected by adding a fresh quantity. The vat is then to be raked; after two hours more lime is added, and the process of raking again performed. These operations are to be repeated till the vat is recovered.

Nothing requires more attention in treating a vat of this kind than the distribution of the lime, the principal use of which is to moderate the tendency to putrefaction, and to limit the fermentation to that degree which is necessary to deprive the indigo of its oxygen. If too much lime be added, the necessary fermentation is retarded; and if there be too little, the putrefactive process commences.

Two hours previous to the dyeing operation, the vat should be raked; and to prevent the stuff coming in contact with the sediment, which would produce inequalities in the colour, a cross of wood is introduced. The stuff is then to be completely wetted with pure water a little heated, and being wrung out, it is dipped into the vat, where it is moved about for a longer or a shorter time, according to the depth of shade required. During this operation, it is taken out occasionally to be exposed to the air, the action of which is necessary to change the green colour of the bath into a blue. Stuff dyed blue in this manner must be carefully washed, to carry off the loose particles of colouring matter; and when the shade of blue is deep, they ought even to be cleansed by fulling with soap. This operation does not alter the colour.

What happens in vats of this kind is the separation of an atom of oxygen from the indigo by the action of the fermenting woad. The base of the indigo thus evolved unites to the quicklime, and this compound dissolving in the water, forms the dyestuff. The reason why the air must be so cautiously excluded is, that, by reviving the indigo, it precipitates it from the liquid, and thus deprives the vat of its colouring matter.

Instead of woad, and the other ingredients just mentioned, indigo is deprived of an atom of oxygen, and the base of it dissolved in water by a mixture of bran and potash. Orpiment is also occasionally employed, which has the property of absorbing an atom of oxygen from indigo, and rendering it capable of combining with a base, and of dissolving in water.

The indigo vat employed by the calico-printers is formed by mixing the indigo with the requisite quantity of sulphate of iron to reduce it to its base, and of quicklime to combine with the base evolved, and to cause it to dissolve in water. Such vats are made very deep. The surface, in consequence of exposure to the air, has a blue colour, the indigo being revived. But the liquor, at a little dis-

The colour which is obtained by dyeing with a solution of indigo in sulphuric acid is known under the name of Saxon blue, because the process was first carried on at Grossenhayn, in Saxony, by Counsellor Barth, who made the discovery about the year 1740. This discovery was for some time kept secret, and the method seems to have been originally very complicated. Alumina, antimony, and some other substances, were previously added to the sulphuric acid. These, however, are now omitted, and the indigo alone is dissolved in the acid.

To produce a Saxon blue colour on woollen stuffs, they are prepared with alum and tartar; and in proportion to the shade required, the quantity of solution of indigo put into the bath must be regulated. When a deep shade of Saxon blue is wanted, the stuff must be passed different times through vessels containing such a quantity of colouring matter as is sufficient to give light colours. In this way, by repeated applications, the colours become more uniform.

We are not aware that Prussian blue is employed as a dyeing material for wool; but it is used to a considerable extent in calico-printing, and has an exceedingly good effect when skilfully used. We shall notice its employment in a subsequent part of this article.

III.—Processes for dyeing Silk Blue.

Silk is dyed blue with indigo alone, without any proportion of wood. The proportion of indigo mentioned in the preparation of the indigo vat, and sometimes a larger proportion, is employed, with six pounds of bran and about twelve ounces of madder. According to Macquer, half a pound of madder for each pound of potash renders the vat greener, and produces a more fixed colour in the silk. When the vat is come to, it should be refreshed with two pounds of potash and three or four ounces of madder, and, after being raked, in the course of four hours it is fit for dyeing. The temperature should be so moderated that the hand may be held in it without uneasiness.

The silk, after being boiled with soap, in the proportion of thirty pounds of soap to a hundred of silk, and well cleaned by repeated beatings in a stream of water, must be dyed in small portions, because it is apt to take on an uneven colour. When it has been turned once or oftener in the bath, it is wrung out and exposed to the air, that the green colour may change to a blue. When the change is complete, it is thrown into clear water, and afterwards wrung out. Silk dyed blue should be speedily dried. In damp weather and in winter it is necessary to conduct the drying in a chamber heated by a stove. The silk should be hung on a frame kept constantly in motion. To dye light shades, some dyers employ vats that are somewhat exhausted; but it ought to be observed that the colour thus obtained is less beautiful and less permanent than when fresh vats, containing a smaller quantity of indigo, are employed.

Some addition is required to be made to the indigo, to give silk a deep blue. A previous preparation is necessary, by giving it another colour or ground. For the Turkey blue, which is the deepest, a strong bath of archil is first prepared. Cochineal is also sometimes used instead of archil, for the ground, to render the colour more permanent. A blue is given to silk by means of verdigris and logwood, but it possesses little durability. It might be rendered more permanent by giving it a lighter shade in this bath, then dipping it in a bath of archil, and finally in the indigo vat.

When raw silk is to be dyed blue, such as is naturally white should be selected. Being previously soaked in water, it is put into the bath in separate hanks, as already directed for scoured silks; and as raw silk is found to combine more readily with the colouring matter, the scoured silk, when it can be conveniently done, should be first put into the bath. If archil, or any of the other ingredients which have been already mentioned, are required to give more intensity to the colour, the mode of application is the same as that directed for scoured silk.

IV.—Processes for dyeing Cotton and Linen Blue.

For dyeing cotton and linen blue, Pileur d'Apigny recommends a vat containing about 120 gallons. From six to eight pounds of indigo, reduced to powder, are boiled with a ley drawn off from a quantity of lime equal in weight to the indigo, and a quantity of potash double its weight. During the boiling, which is to be continued till the indigo is completely penetrated with the ley, the solution must be constantly stirred, to prevent the indigo from being injured by adhering to the bottom of the vessel.

During this process another quantity of quicklime, equal in weight to the indigo, is to be slaked. Twenty quarts of warm water are added, in which is to be dissolved a quantity of sulphate of iron equal to twice the weight of the lime. The solution being completed, it is poured into the vat, which is previously half filled with water. To this the solution of indigo is added, with that part of the ley which was not employed in the boiling. The vat must now be filled up to within two or three inches of the top. It must be raked twice or thrice a day till it is completely prepared, which is generally the case in forty-eight hours, and sometimes sooner, as it depends on the temperature of the atmosphere. A small proportion of bran, madder, and woad, is recommended by some to be added to such a vat as we have now described.

The process which is followed at Rouen, and described by Quatremere, is simpler. The vats, which are constructed of a kind of flint, are coated within and without with fine cement, and are arranged in one or more parallel lines. Each vat contains four hogsheads of water. The indigo, to the amount of eighteen or twenty pounds, being macerated for a week in a caustic ley strong enough to bear an egg, is ground in a mill; three hogsheads and a half of water are put into the vat, and afterwards twenty pounds of lime. The lime being thoroughly slaked, the vat is raked, and thirty-six pounds of copperas are added; and when the solution is complete, the ground indigo is poured in through a sieve. It is raked seven or eight times the same day, and after being left at rest for thirty-six hours, it is in a state fit for dyeing.

In extensive manufactories it is necessary to have vats set at different times. In conducting the process of dyeing, the stuffs are first dipped in the most exhausted vat, and then regularly proceeding from the weakest to the strongest, if they have not previously attained the desired shade. The stuffs should remain in the bath only about five or six minutes, for in that time they combine with all the colouring matter they can take up. After the stuffs have been dipped in a vat, it should not be used again till it has been raked, and has stood at least twenty-four hours, unless it has been lately set, when a shorter period is sufficient.

After the stuffs have been dipped three or four times in a vat, it begins to change. It becomes black, and no blue or copper-coloured streaks are seen on the surface after raking it. It must then be renewed by adding four pounds of copperas with two of quicklime, after which it must be raked twice. In this way a vat may be renewed three or four times; but the additional quantity of ingredients must be diminished as the strength of the vat is exhausted.

A vat which is still more simple and more easily prepared has been recommended by Bergman. The proportion of the ingredients which he has directed to be employed is the following. To three drachms of indigo reduced to powder, three drachms of copperas, and three of lime, add two pints of water. "Let it be well raked, and in the course of a few hours it will be in a proper state for dyeing."

Haussmann employs a still smaller proportion of indigo. For 3000 lbs. of water he takes thirty-six lbs. of quicklime slaked in 200 lbs. of water, with which the indigo in the proportion of from ten to twenty lbs. well ground is to be mixed. He then dissolves thirty lbs. of copperas in 120 lbs. of hot water. The whole being left at rest for fifteen minutes, the vat is filled, and gently and constantly stirred. When a deeper shade is wanted, and particularly when linen is to be dyed, the proportion of indigo should be greater; but the shade depends very much on the time the stuffs remain in the vat, and the times it has been used. When the vat becomes turbid, the process of dyeing must be interrupted till it has been again raked, and the supernatant liquor become transparent. If the effects of the lime fail, a new quantity, fresh slaked, must be added; and if the iron cease to produce the effect on the indigo, a new portion must be also added, observing the precaution to have a greater quantity of lime than what is necessary to saturate the sulphuric acid. When the indigo seems to be exhausted, fresh portions ground in water are also to be added; the vat is to be raked several times, and allowed to settle, after which it is again fit for use. In this way Mr Haussmann informs us he preserved a vat for the space of two years; and had it not been for the accumulation of sediment, which prevented the stuffs from being immersed to a sufficient depth, it might have been continued in use for a much longer time. It is worth while to add, that Mr Haussmann found that a pattern of cloth dipped in water acidulated with sulphuric acid, immediately after it was taken out of the bath, became of a much deeper blue than a similar pattern exposed to the air, or another dipped in river water.

Another convenient and expeditious vat is mentioned by Bergman and described by Scheffer. Indigo reduced to fine powder, in the proportion of three drachms to a quart, is added to the strong ley of the soap boiler. After a few minutes, when the colouring matter is well penetrated by the ley, six drachms of coloured ornament are to be added. In a few minutes after the bath has been well raked it becomes green, and the blue streaks appear on the surface. Heat is to be applied, when the operation of dyeing may commence.

The preparation employed for printing cottons is similar to the above bath, excepting in the proportions of ornament and indigo, which are greater in the former; but these proportions are very different in different manufactories.

The colour denominated English blue is produced by the solution of indigo in sulphuric acid, to which Bancroft gave the improper name of sulphate of indigo. To give silk this colour, it is first to be dyed a light blue; and, when taken out of this bath, it is dipped in hot water, washed in a stream, and left in a bath composed of the sulphate of indigo, to which a little of the solution of tin has been added, until the proper shade is obtained, or the bath is exhausted. Previous to its being put into this bath, it may be dipped in a solution of alum, in which it should remain only a very short time. Silk which has been dyed according to this process is free from the reddish shade which it derives from the blue vat, as well as from the greenish cast of the Saxon blue.

The sulphate of indigo has been hitherto only applied for the purpose of dyeing wool and silk. The affinity of indigo for vegetable substances is not sufficiently strong to effect the decomposition of the sulphate. It cannot, therefore, be employed with advantage in dyeing cotton and linen.

Sect. IV.—Of Black.

Though black, considered optically, is not a colour, but in the absence of the power of reflecting light, it constitutes a very important colour in the estimation of the dyer.

I.—Description of the Dyestuffs.

There are few substances which have the property of producing a permanent black colour without any addition. The juice of some plants produces this effect on cotton and linen. A black colour is obtained from the juice of the cashew nut, which will not wash out, and even resists the process of boiling with soap or alkalies. The cashew nut of India is employed for marking linen. That of the West Indies (anacardium occidentale, Lin.) also yields a permanent dye, but the colour has a brownish shade. The juice of some other plants, as that of the toxicodendron, or sloes, affords a durable bluish black colour; but these substances cannot be obtained in sufficient quantity, even if they afforded colours equal to those produced by the common processes.

The principal substances which are employed to give a black colour are gallnuts, which contain the astrigent principle or tan, and the red oxide of iron. These have been described either in a preceding part of this article, or under the article Chemistry, to which therefore we refer the reader. The black colour is produced by the combination of the astrigent principle with the oxide of iron, held in solution by an acid, and fixed on the stuff. When the particles are precipitated from the mixture of tan and a solution of iron, they have only a blue colour; but after they are exposed for some time to the air, and moistened with water, the colour becomes deeper, although the blue shade is still perceptible. After the particles are fixed on the stuff, the shade becomes much deeper.

Logwood is not to be considered as affording a black dye, but is much employed to give a lustre to black colours. We have already described its nature and properties among the substances from which red colouring matters are obtained.

Black colours are rarely produced by a simple combination between the colouring matter and the stuff, but are usually fixed by means of mordants, as in the case of the black particles which are the result of a combination of

---

1 Berthollet, II. 90. 2 Ibid. ii. 319. 3 Oak bark has been recommended as a substitute for gallnuts in dyeing black, and particularly in dyeing hats; and it is said that the colour thus obtained is fuller, more beautiful and durable, while the operation is easier, and less liable to accident. It was first proposed in the year 1782, by Stephanopoli, a Corsican, and a surgeon in the French army. The examination of the process was referred by the French government to Macquer, who gave a favourable report of it; and afterwards to Berthollet, who gave a different opinion. The process has since been examined, and promises to be more economical and advantageous, especially for dyeing hats. (Phil. Mag. vi. 176.) the astringent principle and the oxide of iron, held in solution by an acid. But when the particles are precipitated from the mixture of an astringent and a solution of iron, they have only a blue colour. By being exposed to the air, and moistened with water, the colour becomes deeper, although the blue shade is still perceptible. No fine black colour is ever obtained, unless the stuffs are freely exposed to the air. In dyeing black, therefore, the operations must be conducted at different intervals. Berthelot has observed that black stuffs, when brought in contact with oxygen gas, diminish its volume, so that some portion of it is absorbed.

II.—Of the Processes for dyeing Woollen Black.

In dyeing woollen stuffs black, if a full and fine deep colour is wanted, it is necessary that they be previously dyed of a deep blue colour. To remove all the particles of colouring matter which happen to be loosely attached to the stuff, it should be washed in a river as soon as it is taken out of the vat, and afterwards cleansed at the fulling mill. After these preliminary processes, the stuffs are ready to receive the black colouring matter. The process of Hellot is the following:

For every hundred pounds of stuff, ten pounds of logwood, and ten pounds of galls reduced to powder, are put into a bag, and boiled in a middle-sized copper, with a sufficient quantity of water, for twelve hours. A third of this bath is put into another copper, along with two pounds of verdigris. The stuff is immersed in this bath, and continually stirred for two hours. The bath should be kept hot, but it ought not to boil. At the end of two hours the stuff is taken out, and a similar portion of the bath is put into the copper, with eight pounds of copperas (sulphate of iron). During the solution of the copperas the fire is diminished, and the bath is allowed to cool for half an hour, stirring it well the whole time. The remainder of the bath is then to be added, and after making this addition, the bag containing the astringent matters should be strongly pressed, to separate the whole. A quantity of sumach, from fifteen to twenty pounds, is now to be added, and the bath is just raised to the boiling temperature; and when it has given one boil it is to be immediately stopped with a little cold water. A fresh quantity of sulphate of iron, to the amount of two pounds, is then added, and the stuff is kept in it for another hour, after which it is taken out, washed, and aired; it is again put into the copper, and constantly stirred for an hour. It is then carried to the river, well washed, and fulled. To soften the black colour, and make it more firm, another bath is prepared with weld. This is made to boil for a moment, and when it has cooled, the stuff is passed through it. By this process, which is indeed somewhat complicated, a beautiful black colour is produced.

But the processes usually followed for dyeing black are more simple. Cloth which has been previously dyed blue is merely boiled in a vat of galls for two hours. It is then kept two hours, but without boiling, in the bath of logwood and sulphate of iron, and afterwards washed and fulled. According to Hollot's process, a bath is to be prepared of a pound and a half of yellow wood, five pounds of logwood, and ten pounds of sumach, which is the proportion of the ingredients for every fifteen yards of deep blue cloth; and the cloth having boiled in this bath for three hours, ten pounds of sulphate of iron are added; the cloth is allowed to remain for two hours longer, when it is taken out to be aired, after which it is again returned to the bath for an hour, and then washed and fulled.

When stuffs are to be dyed at a less expense, instead of the blue ground, a brown or root-coloured ground may be substituted. This brown or fawn colour is communicated by means of the root of the walnut tree, or green walnut peels. The stuffs are then to be dyed black, according to some of the processes already described.

The proportions of the ingredients employed by the Process of English dyers are, for every hundred pounds of cloth pre-the Eng- venously dyed a deep blue, about five pounds of sulphate of iron, five pounds of galls, and thirty of logwood. The first step in the process is to gall the cloth, after which it is passed through the decoction of logwood, to which the sulphate of iron has been added.

The leaves of the arbutus unedo have been recom-mended and employed as a substitute for galls. The used for leaves must be carefully dried, so that the green colour galls may be preserved. A hundred pounds of wool are boiled with sixteen pounds of sulphate of iron and eight of tartar for two hours. The day following the cloth is to be rinsed, as after aluming. A hundred and fifty pounds of the leaves of unedo are then to be boiled for two hours in water, and after being taken out, a small quantity of madder is to be added to the liquor, putting in the cloth at the same time, which is to remain about an hour and a half. It is then taken out and rinsed in water.1 By this process, it is said, blue cloth receives a pretty good black, but white cloth becomes only of a deep brown. It is said, too, that the madder and tartar are useless ingredients.

After the different operations for dyeing the cloth have been finished, it is washed in a river, and fulled, till the ration water comes off clear and colourless. Soap suds are recommended by some in fulling fine cloths, but it is found difficult to free the cloth entirely from the soap. After the cloth has come from the fulling-mill, some propose to give it a dip in a bath of weld, by which it is said to be softened, and the colour better fixed; but, according to Lewis, this operation, which in other cases is of some advantage, is useless after the cloth has been treated with the soap suds.

III.—Of the Processes for dyeing Silk Black.

In communicating a black colour to silk, different operations are necessary, such as boiling, galling, repairing the bath, dyeing, and softening.

To give a deeper shade to silk, it is necessary to deprive it of the gummy substance to which its stiffness and elasticity are owing. This is done by boiling the silk four or five hours with one fifth its weight of white soap, and afterwards beetleing and carefully washing it.

In conducting the process of galling silk, three fourths of its weight of galls are to be boiled for three or four hours; but the proportion of galls must depend on their quality. After the boiling, the liquor is allowed to remain at rest for two hours; the silk is then put into the bath, and left there from twelve to thirty-six hours, when it is to be taken out, and washed in the river. But as silk is capable of combining with a great proportion of the astringent principle, or tan, from which it receives a considerable increase of weight, it is allowed to remain for a longer or shorter time, as the silk is required to have more or less additional weight. To communicate, therefore, to silk, what is called a heavy black, it is allowed to remain longer in the gall liquor: the process is repeated oftener, and the silk is also dipped in the dye a greater number of times.

While silk is preparing for the process of dyeing, the Dyeing bath is to be heated, and should be occasionally stirred, that the grounds which fall to the bottom may not acquire too much heat. It should always be kept under the boiling temperature. Gum and solution of iron are added in different proportions, according to the different processes. When the gum is dissolved, and the bath near the boiling temperature, it is left to settle for about an hour. The silk, which in general is previously divided into three parts, that each may be successively put into the bath, is immersed in it. Each part is then to be three times wrung, and after each wringing hung up to air. The silk being thus exposed to the action of the air, acquires a deeper shade. This operation being finished, the bath is again heated, with the addition of gum and sulphate of iron; and this is repeated two or three times, according as the black required is light or heavy. When the process of dyeing is finished, the silk is rinsed in a vessel with some cold water, by turning or shaking it over.

Silk, after it has been taken out of the dye, is extremely harsh, to remove which it is subjected to the operation of softening. A solution of four or five pounds of soap for every hundred pounds of silk is poured through a cloth into a vessel of water. The solution being completed, the silk is immersed, and allowed to remain in it for about fifteen minutes; it is then to be wrung out and dried.

When raw silk is to be dyed, that which has a natural yellow colour is preferred. The galling operation must be performed in the cold, if it be proposed to preserve the whole of the gum, and the elasticity which it gives to the silk; but if part only of the gum is wished to be preserved, the galling is to be performed in the warm bath.

The dyeing operation is also performed in the cold. All that is necessary is to add the sulphate of iron to the water in which the stuff is rinsed. By this simple process the black dye is communicated. It is then washed, once or twice beetleed, and dried without wringing, that its elasticity may not be destroyed. Raw silk may be dyed by a more speedy process. After galling, it may be turned or shaken over in the cold bath; and thus, by alternately dipping and airing the stuff, the operation may be completed. It is then to be washed and dried, as in the former process.

The method of dyeing velvet at Genoa, which has been simplified and improved in France, is thus described by Macquer. For every hundred pounds of silk, twenty pounds of Aleppo galls, reduced to powder, are boiled in a sufficient quantity of water for an hour. The bath is allowed to settle till the galls have fallen to the bottom; they are then taken out, and two pounds and a half of sulphuric acid, twelve pounds of iron filings, and twenty pounds of gum, are put into a copper vessel, or cullender, furnished with two handles. This vessel is immersed in the bath, and supported that it may not touch the bottom. The gum, which is allowed to dissolve for an hour, is to be occasionally stirred; and if it appear that the whole of the gum is dissolved, three or four pounds more are to be added. Excepting during the operation of dyeing, the cullender is to remain in the copper, which must be kept hot the whole time, but at a temperature below the boiling point. In galling the silk, one third of Aleppo galls is employed, and the stuff should remain six hours in the liquor the first time, and twelve hours the second. By frequent additions of sulphate of iron, and repeated immersions of the stuff, a fine black, according to Lewis, has been obtained. In the above process, the proportion of sulphate of iron is too small; and the gum, according to some, being carried off in the washing, may be considered as useless. Berthollet thinks, that although the quantity be excessive, it has some effect in keeping up the bath; and he adds, if it is to be diminished, it would be useful to add the sulphate of iron in separate portions during each interval.

To diminish the quantity of galls, which are an expensive ingredient in dyeing silk black, other substances have been proposed as substitutes. With this view the following process is recommended.

The silk being boiled and washed, is immersed in a strong decoction of green walnut peels, and allowed to remain till the colouring matter of both is exhausted. It is then to be slightly wrung out, dried, and washed. To give the silk a blue ground, logwood and verdigris are employed, in the proportion of one ounce of the latter for every pound of silk. The verdigris is dissolved in cold water, and the silk is allowed to remain two hours in this solution. It is then immersed in a strong decoction of logwood, slightly wrung out, dried, and afterwards washed at the river. The bath is prepared by macerating two pounds of galls and three of sumach in twenty-five gallons of water, over a slow fire, for twelve hours. The liquid being strained, three pounds of sulphate of iron and the same quantity of gum-arabic are to be dissolved in it. The silk is dipped in this solution at two different times; it is to remain in the bath two hours each time, and it must be aired and dried between each dip. After being twice beetleed at the river, it is dipped a third time, and left in the bath four or five hours, after which it is to be dried, washed, and beetleed, as before. The temperature of the bath should not exceed 120°. After the first dippings, it may be necessary to add half a pound of sulphate of iron, and an equal quantity of gum-arabic.

Silk which has been previously dyed blue with indigo, it is said, takes only a mealy black; but when it has been prepared with logwood and verdigris, it acquires a velvety lustre. A fine black may be obtained from green walnut peel; but the addition of logwood and verdigris renders a smaller quantity of sulphate of iron necessary, and this is of importance, because it is apt to weaken the silk. The only use of galls, according to some, is to increase the weight of the silk; for the purposes of dyeing, sumach is considered sufficient.

IV.—Of the Processes for dyeing Cotton and Linen Black.

It is more difficult to communicate a fine black to linen or cotton than to silk or woollen stuffs. To succeed in producing a black colour of that degree of intensity which will resist soap, it is necessary to adopt particular processes. In dyeing animal matters black, as silk and wool, the best colours are obtained on those which have been previously dyed blue. This also is an essential preliminary process in dyeing linen and cotton black; for it is found that the process which succeeds best is first to give a deep blue grain to the cotton or linen.

The first part of the process is the operation of galling. The stuffs, which have been previously dyed blue, wrung out, and dried, are kept twenty-four hours in the gall liquor, composed of four ounces of galls to every pound of thread. A bath is then prepared of a solution of iron in acetic acid. This solution is obtained by saturating the acid with oxide of iron. In France, vinegar, small beer, or small wine, is employed for this purpose. To promote the acid fermentation, rye meal, or some other substance, is added, and pieces of old iron are thrown into the liquid, which are allowed to remain for six weeks or two months, that the acid may be saturated with the iron. This solution, called iron liquor in this country, is prepared from fermented worts, to which old iron is added, as is described above. Five quarts of the iron liquor for every pound of stuffs are put into a vessel. In this the stuffs are wrought with the hand, pound by pound, for fifteen mi-

---

1 The decoction of walnut peels is prepared by boiling for fifteen minutes, after which it is taken from the fire. After it has subsided, the silk, which has been previously immersed in warm water, is dipped in it. * Berthollet, ii. 29. notes; they are then wrung out and aired. This operation is to be again repeated, taking care to add a fresh quantity of the iron liquor, which should be carefully scummed, after which the stuffs are to be wrung out, aired, and washed at the river. In the next operation, a pound of alder bark for every pound of stuff is boiled in a sufficient quantity of water for an hour. One half of the bath which was employed in the galling, and about one half the quantity of sumach as of alder bark, are then added. The whole is boiled together for two hours, and strained through a sieve. When this liquid is cold, the stuffs are immersed, wrought pound by pound, and occasionally aired. They are afterwards put into the bath, and, after remaining for twenty-four hours, are wrung out and dried. The above is the process which, according to D'Apligny, is followed at Rouen for dyeing cotton and linen.

The process followed at Manchester, which is described by Mr Wilson, is the following. For the operation of galling, galls or sumach are employed. The stuff is afterwards dyed in a bath consisting of a solution of iron in acetic acid. This bath is also frequently composed of alder bark and iron. After having passed through this bath, the stuff is dipped in a decoction of logwood, to which a small quantity of verdigris has been added. This process is to be repeated till a black of sufficient intensity is obtained, observing to wash and dry after each operation.

According to Gublieche, a solution of iron may be prepared by the following process. A pound of rice is to be boiled in twelve or fifteen quarts of water, till the whole is dissolved. A sufficient quantity of old iron made red hot, to reach half way to the surface of the liquor, is thrown into the solution. The vessel in which the solution is kept must be under cover, but exposed to the air and light, at least for a week. In another vessel, containing a quantity of warm vinegar equal to the solution of rice, an equal quantity of red-hot iron is to be put. This vessel must also be exposed in the same way to the air and light. After several days, the contents of both vessels are mixed together, and the mixture is to be exposed for a week to the open air, after which it is to be decanted and kept for use in a close vessel. To give a sufficient black to linen and cotton, it is only necessary, it is said, to steep them twenty-nine hours in this solution; and if it should appear that the liquor is exhausted of colouring matter, a fresh portion is to be employed. In this way a fine permanent black is obtained. According to the same author, this solution may be advantageously employed as a substitute for sulphate of iron, in dyeing silk and wool. But to give them a fine black, silk and woollen stuffs must be dipped in a decoction of logwood after they are taken from the bath.

Sect. V.—Of Brown.

The last of the simple colours is brown. This is also known under the name of fawn colour (fauve, Fr.). It is that brown colour which has a shade of yellow, and might perhaps be considered as a compound colour, although it is communicated to stuffs by one process.

I.—Of the Substances employed in Dyeing Brown.

The vegetable substances which are capable of inducing a fawn or brown colour on different stuffs are very numerous, but those chiefly employed for this purpose are walnut peels and sumach. The peels constitute the green covering of the nut; they are internally of a white colour, which is converted into brown or black by exposure to the air. The skin, when impregnated with the juice of walnut peels, becomes of a brown or almost black colour. When the inner part of the peel, taken fresh, is put into weak oxymuriatic acid, it assumes a brown colour. If the decoction of walnut peels be filtered and exposed to the air, its colour becomes of a deep brown; the pellucides on evaporation are almost black; the liquor detached from these yields a brown extract, completely soluble in water. The colouring particles are precipitated from a decoction of walnut peels by means of alcohol, and they are soluble in water. No apparent change is at first produced by a solution of potash; but it gradually becomes turbid, and the colour is deepened. A copious precipitate, of a fawn colour, approaching to an ash colour, is produced in a decoction of walnut peels, by means of a solution of tin, and the remaining liquor has a slightly yellow tinge.

A decoction of walnut peels yields a small quantity of Properties. fawn-coloured precipitate by means of a solution of alum, and the liquor remains of the same colour. Sulphate of copper renders it slowly turbid, and throws down a small quantity of precipitate of a brownish-green colour, leaving the supernatant liquor of the same colour. Sulphate of iron deepens the colour; when diluted, the colour becomes brownish green, without the deposition of any sediment. Sulphate of zinc also deepens the colour, and produces no precipitate. The same properties are exhibited by a decoction of the walnut-tree wood, but the colouring matter is not obtained from it in such abundance as from the peels; and the bark may also be used with advantage in dyeing.

The affinity of the colouring matter of walnut peels for Advan-wool is very strong; and it readily imparts to it a durable tage-colour, which even mordants do not seem capable of increasing, but they are generally understood to give it additional brightness. A lively and very rich colour is obtained with the assistance of alum. Walnut peels afford a great variety of pleasing shades; and as they require not the intervention of mordants, the softness of the wool is preserved, and the process of dyeing becomes both cheap and simple.

Walnut peels are not gathered till the nuts are com-prepara-tively ripe, when they are put into large casks, along with as much water as is sufficient to cover them. When used in dyeing at the Gobelins in Paris, Berthollet informs us, they are kept for upwards of a year, and very extensively used; but if not made use of till the end of two years, they yield a greater quantity of colouring matter, at which time their odour has become peculiarly disagreeable and fetid. The peels separated from the nuts before they arrive at maturity, may likewise be used in dyeing, but in this state they do not keep so long.

Sumach (rhus coriaria, Lin.) is a shrub produced na-Sumach. turally in Palestine, Syria, Portugal, and Spain, being carefully cultivated in the last two of these countries. Its shoots are annually cut down, dried, and reduced to powder in a mill, by which process they are prepared for the purposes of dyeing.

The infusion of sumach, which is of a fawn colour with Properties. a greenish tinge, is changed into a brown by exposure to the air. A solution of potash has little action on the recent infusion of sumach; its colour is changed to yellow by the action of acids; the liquor becomes turbid by means of alum, a small quantity of precipitate being at the same time formed, and the supernatant liquor remaining yellow. A copious precipitate of a yellowish-green colour is thrown down by sulphate of copper, and the liquor remains clear. No change is speedily produced by muriate of soda (common salt), but it becomes rather turbid at the end of some hours, and its colour is rather clearer. Sulphate of copper produces a copious precipitate of a yellowish green, which after standing some hours changes to a brownish green; the supernatant liquor, which is slightly yellow, remains clear. Sulphate of zinc renders the liquor turbid, darkens its colour, and produces a deep blue precipitate; but when the sulphate of zinc is pure, the precipitate, which is of a brownish fawn colour, is in very small quantity. Acetate of lead gives a copious precipitate of a yellowish colour; the supernatant liquor is of a clear yellow colour. No astringent has so strong a resemblance to galls as sumach; but the precipitate thrown down from an infusion of it by a solution of iron, is not so copious as that which is yielded by an equal quantity of galls, on which account sumach may be generally employed as a substitute for galls, only its quantity will require to be increased.

The bark of the birch tree (Betula alba, Lin.) yields a decoction of a clear fawn colour, but it soon becomes turbid and brown. The addition of a solution of alum, in the open air, produces a copious yellow precipitate; a solution of tin gives also a copious precipitate of a clear yellow colour. With solutions of iron the decoction of the birch tree strikes a black colour, and it dissolves in considerable quantity the oxide of iron, but in smaller proportion than the decoction of walnut peels. On account of this property, it is employed in the preparation of black vats for dyeing thread.

Sandalwood or sandal wood (Pterocarpus santalinus) is also employed for the purpose of giving a fawn colour. There are three kinds of sandal wood, the white, the yellow, and the red. The last only, which is a compact heavy wood, brought from the Coromandel coast, is used in dyeing. By exposure to the air it becomes of a brown colour; when employed in dyeing, it is reduced to fine powder, and it yields a fawn colour with a brownish shade, inclining to red. But the colouring matter which it yields of itself is in small quantity, and it is said that it gives harshness to woollen stuffs. When it is mixed with other substances, as sumach, walnut peels, or galls, the quantity of colouring matter is increased; it gives a more durable colour, and produces considerable modifications in the colouring matter with which it is mixed. Sandal wood yields its colouring matter to brandy, or diluted alcohol, more readily than to water.

Soot communicates to woollen stuffs a fawn or brown colour, of a lighter or deeper shade, in proportion to the quantity employed; but the colour is fading, and its affinity for wool is not great; and besides leaving a disagreeable smell, it renders the fibres harsh. In some manufactories it is employed for browning certain colours, and it produces shades which could not otherwise be easily obtained.

II.—Of the Processes for dyeing Woollen, &c. a Fawn or Brown Colour.

With walnut peels.

In dyeing with walnut peels, a quantity proportioned to the quantity of stuff, and the intensity of shade wanted, is boiled for fifteen minutes in a copper. All that is necessary in dyeing with this substance is, to moisten the cloth or yarn with warm water previous to its immersion in the copper, in which it is to be carefully stirred till it has acquired the proper shade. This is the process if the aluminoous mordant is not employed. In dyeing cloth, it is usual to give the deepest shades first, and the lighter ones afterwards; but in dyeing woollen yarn, the light shades are given first, and the deeper ones afterwards. An additional quantity of peels is joined to each parcel.

Berthollet made a number of experiments to ascertain the difference of colour obtained from the simple decocation of walnut peels, and the addition of metallic oxides as mordants. The oxide of tin, he found, yielded a clearer and brighter fawn colour than that of the simple decoction. The oxide of zinc produced a still clearer colour, inclining to ash or gray. The colour from oxide of lead had an orange cast, while that from oxide of iron was of a greenish brown.

A fawn colour, which has a shade of green, is obtained from sumach alone; but to cotton stuffs which have been impregnated with printers' mordant, or acetate of alumina, sumach communicates a good and durable yellow. Here, however, some precaution is necessary in the use of this substance for this purpose; for as the colouring matter is so fixed a nature, the ground of the stuff cannot be bleached by exposure on the grass. This inconvenience is avoided by impregnating the whole of the stuff with different mordants, producing in this way a variety of colours, and leaving no part white.

Vogler employed the tincture of sanders wood for dyeing patterns of wool, silk, cotton, and linen, having previously impregnated them with a solution of tin, and afterwards washing and drying them. Sometimes he used the solution unmixed, and at other times added six or ten parts of water, and in whatever way he employed it he obtained a poppy colour. When the mordant employed was the solution of alum, the colour was a rich scarlet; with sulphate of copper it was a clear crimson, and with sulphate of iron a beautiful deep violet.

CHAPTER V.

OF COMPOUND COLOURS.

A mixture of two colouring substances, it is well known, produces a very different shade from that of either of the uncombined colouring matters; hence compound colours are obtained, which are merely mixtures of simple colours. It would undoubtedly be a desirable thing to ascertain with accuracy the peculiar shade produced by the combination of two colouring matters; but these results can only be certainly known by experiment, because by the action of different substances in the bath they are subject to great variations in their effects, according to the affinities which are brought into action, and the new combinations which are formed. What is natural to colouring particles is not to be considered as a constituent part of compound colours, but only the difference of shade which they ought to assume with a particular mordant, or in a particular bath. The effects, therefore, of the chemical agents employed in these processes, and the result of different combinations, ought to be particularly attended to. It is in dyeing compound colours that skill and ingenuity are most conspicuous, and their application of greatest utility, to enable the dyer to vary his processes according to the shade desired, and at the same time to accomplish his operations by the shortest and cheapest means.

As compound colours are obtained by the mixture of simple colours, very different shades will be obtained from very different proportions of the simple colours; hence compound colours exhibit an indefinite variety of shade, and the processes by which they are produced are very numerous. It would extend this treatise to an unusual length were we to attempt to describe every variety of shade which is obtained from the mixture of simple colours. We shall therefore limit our observations to some of the principal

1 Elements of Dyeing, ii. 296. 2 Creil, Ann. 1790. Compound colours, and an account of the processes by which they are obtained, leaving it to our readers, who have made themselves familiar with the principles already detailed, to vary these colours by employing different proportions and different combinations of simple colouring matters.

Compound colours have been usually divided into four classes, namely, green, purple, orange, and gray or drab colour. These are obtained from mixtures of the following simple colours:

1. Blue and yellow produce a green. 2. Red and blue produce a purple, &c. 3. Red and yellow produce orange. 4. Black and other colours produce gray, &c.

The following sections will be occupied in a short detail of the methods which are usually employed in producing these different compound colours.

Sect. I.—Of the Mixture of Blue and Yellow, or Green.

Green colours, from the great variety of shades which they exhibit, have been long known by different names, by which the intensity of shade is characterized, such as sea-green, apple-green, meadow or grass-green, pea-green, parrot-green, &c. Many plants afford a green colour, such as brome grass (bromus secalinus, Lin.) green berries of rhinanthus frangula, wild chervil (charophyllum sylvestre, Lin.), purple clover (trifolium pratense), common reed (arundo phragmites). These colours, however, do not possess sufficient permanency. According to D'Ambourney, indeed, a permanent green may be obtained from the fermented juice of the berries of the berry-bearing alder (rhinanthus frangula). Having previously prepared the cloth with tartar, solution of nitrate of bismuth, and common salt, he added to the fermented juice of the berries, after it was warmed, a small proportion of acetate of lead; and in this bath he communicated to the cloth an intermediate shade between parrot and grass green. But it is usually from the mixture of blue and yellow that green is obtained; and it may be observed, that it requires much skill and experience, especially in giving light shades, to produce a colour which is uniform and entirely without spots.

I.—Of the Processes for dyeing Woollen Stuff's Green.

To dye woollen green, either the yellow or the blue dye may be given to it first. But when the stuff is first dyed yellow, and in this state is introduced into the blue vat, part of the yellow colouring matter being dissolved in the vat, communicates to it a green colour, which renders it unfit for dyeing any other colour than green. To avoid this inconvenience, therefore, the blue colour is first given, and afterwards the yellow. It would be quite unnecessary to resume the account of any part of the processes for dyeing blue, which have been already detailed. It is proper, however, to add, that the intensity of the blue shade must be proportioned to the green, or to the depth of the green colour which is wished to be obtained. Thus, for instance, to produce a parrot green, a ground of sky blue is given, and for the green like that of a drake's neck, a deep blue is required. When the blue dye has been communicated, the yellow is afterwards given, according to some of the processes which have been already described for dyeing yellow. The proper ground being communicated to the cloths, they are washed in the fulling mill, and boiled as for the common process of welding; but when the shade is light, the proportion of salts should be less. Cloths which are to receive light shades are first boiled, and when these are taken out, tartar and alum are added in fresh portions till the cloths which are intended for the darkest shades are boiled. The process of welding is conducted in the same way as for dyeing yellow, with this difference, that a larger proportion of weld is employed, excepting for lighter shades, when the proportion must be smaller. In dyeing green, it is usual to have a succession of shades at the same time; the process is begun with the deepest and ends with the lightest. Between each dip there should be an interval of one half or three quarters of an hour, and at each interval water is added to the bath. It is the practice of some dyers to give each parcel two dips, beginning the first time with the deep shades, and the second with the lighter ones; but when this practice is followed, the time of immersion should be shortened. In dyeing very light shades, the bath should never be permitted to reach the boiling temperature. For deep greens, a browning is given with logwood and a small proportion of sulphate of iron.

For some kinds of green, sulphate of indigo is employed; Saxon and in this case either the blue and yellow are dyed separately, or the whole of the ingredients are mixed together in the bath, and the whole process is finished at a single operation. The colour thus obtained has been distinguished by the name of Saxon green. The following is the process recommended by Dr Bancroft.

"The most beautiful Saxon green," says he, "may be produced very cheaply and expeditiously, by combining the lively yellow which results from quercitron bark, muri-sulphate of tin, and alum, with the blue afforded by indigo when dissolved in sulphuric acid, as for dyeing the Saxon blue.

"To produce this combination most advantageously, the dyer, for a full-bodied green, should put into the dyeing vessel after the rate of six or eight pounds of powdered bark in a bag for every 100 pounds weight of cloth, with only a small proportion of water as soon as it begins to grow warm; and when it begins to boil, he should add about six pounds of muri-sulphate of tin (with the usual precautions), and a few minutes after, about four pounds of alum. These having boiled together five or six minutes, cold water should be added, and the fire diminished so as to bring the heat of the liquor nearly down to what the hand is able to bear; and immediately after this, as much sulphate of indigo is to be added as will suffice to produce the shade of green intended to be dyed, taking care to mix it thoroughly with the first solution by stirring, &c.; and this being done, the cloth, previously scoured and moistened, should be expeditiously put into the liquor, and turned very briskly through it for a quarter of an hour, in order that the colour may apply itself equally to every part, which it will certainly do in this way with proper care. By these means, very full, even, and beautiful greens may generally be dyed in half an hour; and during this space it is best to keep the liquor at rather less than a boiling heat. Muri-sulphate of tin is infinitely preferable for this use to the dyer's spirit, because the latter consists chiefly of nitric acid, which, by its highly injurious action upon indigo, would render that part of the green colour very fugitive, as I have found by repeated trials. But no such effect can result from the muri-sulphate of tin, since the muriatic acid has no action upon indigo; and the sulphuric is that very acid which alone is proper to dissolve it for this use.

"Respecting the beauty of the colour thus produced, those who are acquainted with the unequalled lustre and brightness of the quercitron yellows, dyed with the tin basis, must necessarily conclude that the greens composed therewith will prove infinitely superior to any which can result from the dull muddy yellow of old fustic; and in point of expense it is certain that the bark, muri-sulphate of tin, and alum, necessary to dye a given quantity of cloth in this way will cost less than the much greater quantity..." Compound (six or eight times more) of fustic, with the alum necessary for dyeing it in the common way, the sulphate of indigo being the same in both cases. But in dyeing with the bark, the vessel is only to be filled and heated once, and the cloth, without any previous preparation, may be completely dyed in half an hour; whilst in the common way of producing Saxon greens, the copper is to be twice filled; and to this must be joined the fuel and labour of an hour and a half's boiling and turning the cloth in the course of preparation, besides nearly as much boiling in another vessel to extract the fustic; and after all, the dyeing process remains to be performed, which will be equal in time and trouble to the whole of the process for producing a Saxon green with the bark; so that this colour obtained from bark will not only prove superior in beauty, but in cheapness, to that dyed as usual with old fustic.

II.—Of the Processes for dyeing Silk Green.

In giving silk a green colour, greater precaution is necessary, to preserve uniformity of colour, and to prevent spots and stripes. Silk which is intended to receive a green colour is scoured in the same way as for other colours; but for light shades the scouring must be as complete as for blue. Silk which is to be dyed green is first dyed yellow, and being well alumed, it is slightly washed at the river, and divided into small parcels, that it may receive the colouring matter uniformly, and then carefully turned in the weld bath. When the ground is supposed to have acquired a sufficient degree of intensity, a pattern is put into the blue vat to ascertain the proper shade. When this is the case, the silk is taken out of the bath, washed, and immersed in the blue vat. To produce a deeper colour, and at the same time to give variety of shade, a decoction of logwood, fustic, or anotta is added to the yellow bath, after the weld has been taken out. For very light shades, such as apple and sea-green, it is scarcely necessary to add, that a weaker ground is to be given. For all light shades, except sea-green, the process is found to succeed better when the yellow is communicated by baths which have been already used; but these baths should not contain any logwood or fustic.

Saxon green is produced by means of sulphate of indigo. This is a brighter but less durable colour than the former. This process is conducted by boiling as for welding, after which the cloth is washed. Fustic in chips is enclosed in a bag, put into the same bath, and boiled for an hour and a half, when it is taken out, and the bath allowed to cool till the hand can bear it. A pound and a quarter of sulphate of indigo for each piece of cloth of eighteen yards is added. The cloth is at first to be turned quickly, and afterwards more slowly, and it should be taken out before the bath boils. Some dyers put in only two thirds of the solution at first, and after two or three turns take out the cloth and add the other one third. By this means the colour is more uniform.

To produce Saxon green at one operation, the following process is recommended by Dr Bancroft. A bath is prepared of four pounds of quercitron bark, three pounds of alum, and two pounds of muriato-sulphate of tin, with a sufficient quantity of water. The bath is boiled ten or fifteen minutes, and when the liquor is so far reduced in temperature as the hand can bear it, it is fit for dyeing. By adding different proportions of sulphate of indigo, various and beautiful shades of green may be obtained, and the colour thus produced is both cheap and uniform. Care should be taken to keep the bath constantly stirred, to prevent the colouring matter from subsiding. Those shades which are intended to incline most to the yellow should be dyed first; and by adding sulphate of indigo, the green having a shade of blue may be obtained. This process, Dr Bancroft observes, is the most commodious and certain for dyeing most beautiful Saxon greens upon silk.

To produce English green, which is more beautiful than common green, and is said to be more durable than the green Saxon green, Guhlche gives the following process. He first dyes the silk of a light blue in the cold vat already described, then soaks it in warm water, washes it in a stream, and dips it in a weak solution of alum. He then prepares a bath of sulphate of indigo, one ounce of solution of tin, with the tincture of French berries made with aceto-citric acid. The silk is kept in this bath till it has obtained the desired colour. It is then washed and dried in a shady place. Lighter shades may be dyed afterwards.

III.—Of the Processes for dyeing Cotton and Linen Green.

Cotton and linen, after being scoured in the usual way, are first dyed blue, and after being cleansed, they are given dipped in the weld bath, to produce a green colour. The strength of the blue and yellow is proportioned to the shade of green which is wanted. But as it is difficult to give to cotton velvet a uniform colour in the blue vat, it is first dyed yellow with turmeric, and the process is completed by giving it a green with sulphate of indigo. The same result, however, will be obtained by commencing the process either with the yellow or the blue.

The process which D'Apligny describes for dyeing cotton velvet, or cotton thread, a sea or apple green, in one bath, is the following. A quantity of verdigris is dissolved in vinegar, and the mixture is kept excluded from the air in the heat of a stove for fifteen days. A quantity of potash equal in weight to the verdigris employed is dissolved in water, and, four hours before dyeing, it is added to the solution of verdigris. The mixture is to be kept hot. One ounce of alum in five quarts of water for each pound of stuff being prepared, the cotton thread or velvet is soaked in this solution. It is then taken out, and the verdigris being added to the solution of alum, it is again introduced to be dyed.

The different shades of olive green, and drake's neck green, are given to thread after it has received a blue green ground, by galling it, and dipping it in a weaker or stronger bath of iron liquor, then in the weld bath, to which verdigris has been added, and afterwards in the bath with sulphate of copper. The colour is lastly to be brightened with soap.

Cotton dyed with Prussian blue may be dyed green by previously aluming while it is still wet with the blue, and then dipping in a weld bath, the strength of which is proportioned to the shade required. The colour from weld is more lively than that obtained from fustic. But fustic, which gives a deeper shade than weld, and diminishes the brightness of the blue, is to be preferred when a green with an olive shade is wanted.

The shade of green given to any stuff, it is obvious, must vary according to the intensity of the blue shade, remain the strength of the yellow bath, and the nature of the yellow colouring matter employed. Yellow colours are rendered more intense by means of alkalies, sulphate of lime, and ammoniacal salts; but become fainter by means of acids, alum, and solutions of tin. In dyeing Saxon green the result will be different according to the process which is followed. The effects will be different by adding a yellow to a Saxon blue, from the process in which the sulphate of indigo is mixed with the yellow ingre-

---

1 Phil. of Perm. Col. 336. 2 Ibid. 346. 3 Berthollet, ii. 319.

Sect. II.—Of the Mixture of Red and Blue, or Purple, &c.

By the mixture of red and blue, violet, purple, dove-colour, lilac, and a great variety of other shades, according to the proportion of the substances employed, or the predominance of the blue or the red, are produced. In stuffs which are to be dyed violet, a deeper blue must be given; for purple colours, the ground requires to be of a lighter blue; but in lilac and other light colours, it is necessary that both the blue and the red have a light shade.

I.—Of dyeing Wool Violet, Purple, &c.

In the attempts which have been made to communicate a violet or purple colour to a scarlet ground, according to the observations of Heliot, the colour is very unequal. It becomes therefore necessary to give the blue colour first; and for violets or purples, the shade of blue ought not to be deeper than that of sky blue. The stuff being dyed blue, is boiled with alum, and two fifths of tartar, and is afterwards dipped in a bath composed of nearly two thirds the quantity of cochineal required for scarlet, with the addition of tartar. The same process, indeed, as for dyeing scarlet, is followed. It is a common practice to dye these colours after the reddening for scarlet, making such additions of cochineal and tartar as the intensity of the shade may require.

For lighter shades, as lilacs, dove-colours, &c., the stuff may be dipped in the bath which has served for violet and purple, and is now somewhat exhausted, taking care to add a quantity of alum and tartar. For reddish shades, such as a peach-blossom, a small proportion of solution of tin is added. It may be observed in general, that although the proportion of cochineal is less in dyeing lighter shades, the quantity of tartar must not be diminished.

To obtain the same colours, a shorter and less expensive process is recommended by Poerner. In this process he employs sulphate of indigo. He boils the stuff in a solution of alum, in the proportion of three ounces of the latter to one pound of the former, for an hour and a half, and afterwards allows it to remain in the liquid for a night after it has cooled. The dyeing bath is prepared with an ounce and a half of cochineal, and two ounces of tartar, which are boiled for three quarters of an hour: two ounces and a half of sulphate of indigo are then added, the whole is stirred, and boiled gently for fifteen minutes. The dyeing operation is conducted in the usual way, and a beautiful violet is thus obtained. To have all the variety of shades which are produced by the mixture of red and blue, the proportion of the sulphate of indigo is increased or diminished. It is sometimes increased to five ounces, and diminished to five drachms, for each pound of stuff. The quantity of cochineal is also varied, but when it is less than an ounce the colour is dull. Different proportions of tartar are also employed. To produce variety of shades, the stuff is also prepared with different proportions of solution of tin.

To communicate a purple colour to wool, as well as some other shades, logwood, with the addition of galls, has been employed. The stuff is previously dyed blue, compound and, to give a brown shade, sulphate of iron is used; but colours, the colours thus obtained are not permanent. By the following process, described by Decroizille, a durable dye is produced by means of this wood. He dissolved tin in sulphuric acid, to which were added common salt, red acidulous tartrate of potash, and sulphate of copper; or it may be more conveniently done by making a solution of tin in a mixture of sulphuric acid, common salt, and water, to which are to be added the tartrate and sulphate in the state of powder. Of this mordant not less than 1500 quarts were made in twenty-four hours, in a leaden vessel to which a moderate heat was applied. A very lucrative trade was carried on for three years by Decroizille, who sold it at the rate of 1s. 3d. sterling per pound.

If wool in the fleece is to be dyed, it will require a third process of its weight of this mordant, while a fifth is a proportion sufficient for stuffs. A bath is prepared of such a degree of temperature as the hand can bear, with which the mordant is properly mixed, and the wool or stuff dipped in it and stirred; the same degree of temperature being kept up for two hours, and increased a little towards the end; after which it is taken out, aired, and well washed. A fresh bath of pure water is prepared at the same temperature, to which is added a sufficient quantity of the decoction of logwood; the stuff is then immersed, stirred, and the heat increased to the boiling temperature, which is to be continued for fifteen minutes, after which, the stuff being taken out, aired, and carefully rinsed, the process of dyeing is completed. If for every three pounds of wool one pound of decoction of logwood has been used, and a proportionate quantity for stuffs which require less, a fine violet colour is produced, to which a sufficient quantity of Brazil wood imparts the shade known in France by the name of prune de Monsieur.

Logwood and Brazil, fustic and yellow wood, are co-diffusing substances which may be fixed with advantage shades upon wool by means of this mordant. The colour communicated by the two first of these is liable to be changed in the fulling by the action of the soap or urine employed for that purpose; but this change, which is always produced by alkaline substances, is remedied by a slightly acid bath a little hot, called brightening, for which the sulphuric acid has the preference. The colour becomes as deep, and frequently much brighter than before the change. Wools which have been dyed by means of this mordant are said to admit of being spun into a finer and more beautiful thread than by the use of alum. If the use of sulphate of copper is omitted, more beautiful colours are produced by fustic and yellow wood, as well as by weld. An orange-red colour is communicated by madder, but not so deep as with a similar quantity of alum. When sulphate of copper is omitted, the wool is said to become much harsher, and the mordant thus prepared yields but indifferent colours with logwood, and in particular with Brazil wood. The use and carriage of this mordant are inconvenient, on account of the heavy sediment by which the vessel is half filled under a corrosive liquor, capable only of being kept in stone ware. These inconveniences may be remedied by the omission of the water in the receipt, which leaves only a paste more conveniently used, and the carriage of it two fifths cheaper.

The above process is thus explained by Berthollet. The nature of decomposition of the muriate of soda is effected by the action of the sulphuric acid; and the muriatic acid being thus disengaged, dissolves the tin, part of which is precipitated by means of the tartaric acid, producing the sediment already mentioned. The oxide of copper produces the blue with the colouring particles of the logwood; the violet is formed by the oxide of tin with the same wood, Compound and the red with the colouring matter of the Brazil wood.

Colours. The same ingenious chemist farther observes, that as an excess of acid is retained in the liquor, it might probably be of advantage to employ acetate as a substitute for sulphate of copper, in which case the action of the free acid would be moderated. He thinks it would still be more advisable to make use of verdigris; because the uncombined part of the oxide of copper would in that case unite with the excess of acid, on which account a smaller quantity of acid would remain in the liquor; and probably the quantity of tartar might be diminished, as a smaller quantity of tin would thus be precipitated.

II.—Of dyeing Silk Violet or Purple.

Silk is capable of receiving two kinds of violet colours, denominated the fine and the false, the latter of which is produced by means of archil or Brazil wood. When the fine violet colour is required, the silk must first be passed through cochineal, and dipped afterwards in the vat. The preparation and dyeing of the silk with cochineal are the same as for crimson, with the omission of tartar and solution of tin, by means of which the colour is heightened. The quantity of cochineal made use of is always proportioned to the required shade, whether it is more or less intense; but the usual proportion for a fine violet colour is two ounces of cochineal for each pound of silk. When the silk is dyed it is washed at the river, twice beetleed, dipped in a vat more or less strong in proportion to the depth of the violet shade, and then washed and dried with precautions similar to those which all colours require that are dyed in the vat. If the violet is to have greater strength and beauty, it is usual to pass it through the archil bath; a practice which, though frequently abused, is not to be dispensed with for light shades, which would otherwise be too dull.

When silk has been dyed with cochineal according to the above directions, only a very light shade is requisite for purple; the shades which are deepest are dipped in a weak vat, while dipping them in cold water is sufficient for such as are lighter, the water having been incorporated with a small quantity of the liquor of the vat, because in the vat itself, however weak it might be, they would acquire too deep a tinge of blue. In this manner are the light shades of this colour, such as gilly-flower, peach-blossom, &c., produced by diminishing the quantity of cochineal.

There are various ways of imparting to silk what are denominated the false violets; but those which are most frequently used, and possessed of greatest beauty, are prepared with archil, the bath of which is, in point of strength, to be suited to the colour required. Having been beetleed at the river after scouring, the silk is turned in the bath on the skein sticks; and when the colour is deemed sufficiently deep, a pattern is tried in the vat, to ascertain whether it takes the violet colour intended to be produced. If the shade is found to have acquired the proper depth, the silk is beetleed at the river and dipped in the vat, in the same way as for the fine violet colours; and less either of the blue or of the archil colour is given, according as it is meant that the red or blue shade of the violet colour should predominate.

The process recommended by Gubhliche for communicating a violet colour to silk is the following. A pound of silk is to be soaked in a bath of two ounces of alum and a like quantity of solution of tin, after having carefully poured off the sediment formed in the mixture. The dye-bath is prepared with two ounces of cochineal reduced to powder, with a drachm of tartar, and the remaining part of the bath, which has answered the purpose of a colomdant, with the addition of a sufficient quantity of water. When slightly boiled, such a quantity of solution of indigo is added as may communicate to the bath a proper shade of violet; after which the silk is immersed, and boiled till it has acquired the intended shade. It is then wrung, washed in a stream, and, like every other delicate colour, must be dried in the shade. The light shades exhaust the bath. But it ought to be observed that this colour, which is said to be a beautiful violet, possesses but little durability, and is apt to assume a reddish tinge, owing to the colour of the indigo fading first.

A violet colour may be imparted to silks by immersing them in water impregnated with verdigris, as a substitute for alumining, and next giving them a bath of logwood, in which they assume a blue colour, which is converted to a violet, either by the addition of alum to the bath, or by dipping them in a weaker or stronger solution of that substance, which communicates a red colour to the particles of logwood. This violet possesses but a small degree of beauty, and little durability; but if alummed silk be immersed in a bath of Brazil wood, and next in a bath of archil, after washing it at the river, a colour is obtained possessing a much higher degree of beauty and intensity. The process described above for dyeing wood succeeds equally well, according to M. Decroizille, in communicating to silk a violet colour.

III.—Of dyeing Cotton and Linen Violet.

The most ordinary mode by which a violet colour is communicated to cotton and linen stuffs, is first to give them a blue ground in the vat, proportioned to the required shade, and to dry them. They are afterwards galled, in the proportion of three ounces of galls to a pound of stuff, and being left in this bath for twelve or fifteen hours, are wrung out and dried again. They are next passed through a decoction of logwood, and when thoroughly soaked and taken out, the bath receives an addition of two drachms of alum and one of dissolved verdigris for each pound of cotton or thread. The skeins are then dipped again on the skein sticks, and turned for about fifteen minutes, when they are taken out and aired. They are next immersed in the bath for fifteen minutes, taken out, and wrung. To complete the process, the vat employed is emptied; half of the decoction of logwood not formerly made use of is now poured in, with the addition of two drachms of alum, and the thread is again dipped in it till it has acquired the shade proposed, which must always regulate the strength or weakness of the decoction of logwood. This colour resists in a considerable degree the action of the air, but in point of permanency is much inferior to that which is obtained from the use of madder.

Sect. III.—Of the Mixtures of Yellow and Red, or Orange.

Orange is the usual result of a composition of yellow and red colours; but an almost endless variety of shades may be produced, according as we vary the proportion of the ingredients, and the particular nature of the yellow made use of. It is sometimes the practice of dyers to combine blue with yellow and red, the result of which is the colour denominated olive. Many varieties may be obtained from the use of weld, saw-wort, dyers-weed, and other yellows, and by employing tartar, alum, sulphate of zinc, or sulphate of copper, in the bath, or in the preparation of the cloth.

1 Berthollet, ii. 340. I.—Of dyeing Wool Orange.

By a process exactly the same as that which is followed in communicating to stuffs a scarlet colour, an orange may be given to wool; but the quantity of red must be diminished, and that of the yellow increased. If wool is dyed a red colour by means of madder, and afterwards yellow with weld, the resulting compound is a cinnamon colour, and the most proper mordant in this case is a mixture of alum and tartar. The shades may be varied at pleasure by substituting other yellow dyestuffs instead of weld, and by varying the proportions as circumstances may require. Wool may receive a reddish yellow colour by passing it through a madder bath, after it has undergone the usual process for yellow, which has already been described. The strength of the madder bath is always to be proportioned to the shade required. Brazil wood is sometimes employed with yellow substances, or mixed with cochineal and madder. Snuff, chestnut, musk, and other shades are produced by substituting walnut-tree root, walnut peels, or sumach, for weld.

II.—Of Dyeing Silk Orange, &c.

Logwood, Brazil wood, and fustic, communicate to silk a marone and cinnamon colour, together with all the intermediate shades. The silk is scoured in the usual manner, alumed, and a bath is prepared by mixing together decoctions of the three different woods mentioned above, made separately, varying the quantity of each according to the shade intended to be given; but the proportion of fustic should be greatest. The silk is turned in the bath on the skein sticks, and when it is taken out, if the colour be uniform, it is wrung and again dipped in a second bath of these three ingredients, according to the effect produced by the first, in order to obtain the shade required.

The blue vat is not made use of when an olive colour is to be communicated to silk. After being alumed, it is dipped in a bath of weld, which is made very strong. To this is afterwards added the juice of logwood, with a small quantity of solution of alkali when the silk is dipped. This converts it into green, and gives the olive colour. It is dipped again in this bath till it has acquired the shade wanted.

To communicate to it the colour known by the name of rotten olive, fustic and logwood are added to the bath after welding, without any alkali. If the colour wanted is to incline more to a red, the addition of logwood alone is sufficient. A sort of reddish olive may likewise be obtained by dyeing the silk in a fustic bath, to which a greater or less quantity has been added of sulphate of iron and logwood.

III.—Of dyeing Cotton and Linen Orange, &c.

A cinnamon colour is communicated to thread and cotton by commencing the process for dyeing them with verdigris and weld; they are afterwards to be dipped in a solution of sulphate of iron, denominated by the French bain d'asservage, and then wrung out and dried. As soon as they are dried, they are galled in the proportion of three ounces to the pound of stuff; then dried again, alumed as for red colours, and maddered. After being washed and dried, they are put into hot soap suds, and turned till they have acquired a sufficient degree of brightness. It is the practice of some dyers to add to the aluming a decoction of fustic.

By boiling four parts of weld and one of potash in a sufficient quantity of water, M. d'Apligay informs us, a fine olive colour is communicated to cotton and thread. Brazil wood which has been steeped for a night is boiled separately with a small quantity of verdigris, and these solutions are mixed together in various proportions, according to the particular shade required. The thread or cotton is dipped in the compound solution in the usual way.

Sect. IV.—Of the mixture of Black with other Colours.

The compound colours which are obtained from the brown mixture of black and other colours, are brown, gray, drab, &c. according to the nature and proportions of the simple colours employed.

I.—Of dyeing Woollen Stuffs Brown, Gray, &c.

To give a browning to cloth, as soon as it has been dyed, it is dipped in a solution of sulphate of iron, with the addition of an astringent, which makes a black bath. It is more common to mix a small quantity of solution of iron with a bath of water, adding more till the dyed stuff dipped in it has received the intended shade. Sulphate of iron is sometimes added to the dye bath; but by dipping the dyed stuff in a solution of this salt, the end is more easily attained. It is the usual practice of M. Poerner to soak the stuff in a solution of sulphate of iron, to which other ingredients are sometimes added; and after having taken it out of the mordant, it is dipped in the dye bath.

In order to obtain coffee and damascene colours, with other shades of browns of the common dye, the first method is adopted; a colour more or less deep is communicated to them, according to the shade intended to be obtained by the browning; and a bath is made of galls, sumach, and alder bark, with the addition of sulphate of iron. Those stuffs are first dipped to which the lightest shades are to be communicated, and when these are finished, the browner ones are dipped, a quantity of sulphate of iron being added for each operation, proportioned to the effect intended to be produced.

Bluish grays are communicated to stuffs, according to Gray. Poerner, by the solution of indigo in sulphuric acid, combined with a mixture of decoction of galls and sulphate of iron, varying the shades according to the different quantities of these ingredients made use of. If to a bath composed of cochineal, fustic, and galls, sulphate of iron be added, other shades are obtained.

For marone, and such other colours as bear a strong resemblance to it, sanders and galls are employed, and sometimes a browning with the addition of logwood. If dyed in the remains of a cochineal bath, these colours may be made to incline to a crimson or purple; and the same effect is produced by adding a small quantity of madder or cochineal to the bath. A little tartar gives a greater degree of brightness to the colour. With a mixture of galls, fustic, and logwood, and a greater or smaller quantity of madder, with the addition of a little alum; those colours may be communicated to stuffs which are known by the name of hazel.

M. Guhlche produces what is called a pace colour, by Puce co-boiling for fifteen minutes a pound of woollen stuff with four two ounces of alum, a certain proportion of vinegar and solution of iron, after which he leaves it in the mordant for twelve hours. He then makes a bath with the decoction of two ounces of white galls carefully poured off from the sediment, and mixed with four ounces of madder, in which, when it grows hot, the stuff is immersed, after being taken out of the mordant, allowing it to remain there, while the temperature is gradually increased, till the colour intended has been imparted to it; after which it is boiled for two minutes, washed, and dried in the sun. The colour thus obtained possesses a great degree of durability. It is of a deeper brown by the omission of the alum and vinegar in the mordant; and after these colours the lighter shades are dyed. Sumach may be employed as a substitute for Compound half of the madder. Different brown colours, possessing considerable permanency, may likewise be produced by the use of Brazil and logwood, if more or less of a solution of iron be mixed with a decoction of these substances. The wool being previously alumed and galled, is dyed in it.

II.—Of dyeing Silk with Mixtures of Black, &c.

M. Guibiche imparts to silk a purple violet without a blue ground, with a mixture of one part of galls dissolved in white wine, with three parts of water, in which a pound of silk is macerated for twelve hours, soaked in a mordant made up of two ounces of alum, one ounce of solution of tin, and half an ounce of muriatic acid. After wringing the stuff, it is dyed in a bath composed of two ounces of cochineal and a small quantity of solution of iron, till the intended shade has been communicated; and for shades which are lighter, the residua of these baths are sufficient, either separately or mixed together. Madder may be used in the same way, macerating a pound of silk in a solution of alum mixed with an ounce of muriatic acid and a quantity of solution of iron. When the stuff is wrung out, it is dyed in a bath made of eight ounces of madder. When deeper colours are wanted, some of the solution of galls in white wine is mixed with the madder and cochineal baths.

Silk may be dyed in a bath made of equal parts of Brazil and logwood juice, adding a certain quantity of solution of iron after the stuff has been soaked in a solution of two ounces of alum and an ounce of muriatic acid. If solution of galls be added, the colour becomes deeper.

Colours resembling that of brick may be produced by immersing silk in an anotta bath, after preparing it with a solution of galls mixed with a certain quantity of solution of iron. By the mixture of Brazil, logwood, archil, and galls, and by a browning with sulphate of iron, a number of different shades are produced; but the whole of them have more or less a tendency to fade, although their brightness is very pleasing to the eye.

III.—Of dyeing Cotton and Linen with Mixtures of Black, &c.

A permanent violet colour may be given to thread and cotton, when scoured in the ordinary way, by preparing a mordant with two quarts of the bath of what is called the black cask, and four quarts of water, for each pound of stuff, which is made to boil, and the scum is removed which forms on the surface, till it wholly disappears. The liquor is poured into a vat, and, when warm, four ounces of sulphate of copper and one ounce of nitre are dissolved in it. The skeins are left to soak in it for ten or twelve hours, wrung out, and dried. If it is required to produce a deep violet colour, two ounces of verdigris must be added to the bath; and if the nitre be omitted, the colour becomes still deeper by galling the thread more or less prior to its being put into the mordant. If the nitre be increased, and the sulphate of copper be diminished, the violet colour becomes more inclined to lilac. A number of various shades may be produced by different modifications of the mordants employed.

Cotton is galled, dipped, and wrought in the common way, when different shades of marone colour are wanted. To the bath employed must be added more or less of the liquor of the black cask. The cotton is then washed in a bath mixed with verdigris, next welded, and dyed to a fustic bath, to which a solution of soda and alum is sometimes added. When the cotton prepared in this manner has been thoroughly washed, it is next well maddered, dipped in a weak solution of sulphate of copper, and last of all in soap suds.

For some hazel and snuff colours, a browning is communicated to stuffs by means of soot, after the welding and madder bath, to which galls and fustic have been added; sometimes soot is mixed with this bath, and a browning is likewise imparted by means of a solution of sulphate of iron; and for browning colours, walnut peels are sometimes employed as a substitute for solutions of iron. For such wools as are designed for the manufacture of tapestry they are very advantageous, because the colour is not changed into yellow by exposure to the air, as is the case in browning, which is imparted by means of iron, but remains a considerable time without any sensible change. The hue is indeed rather dull, but its goodness and very moderate price are sufficient to recommend a more extensive use of it for grave colours, which in common stuffs are sometimes fashionable.

CHAPTER VI.

OF CALICO-PRINTING.

Calico-printing is the art of communicating different colours to particular parts of the surface of cotton or linen cloth, while the rest of the cloth retains its white colour; or the whole of the cloth may be dyed one colour, as red or blue, except particular parts, to which some other colours, as yellow, orange, green, &c., are given. The process is not confined to linen and cotton cloth; it may be applied also to silk and woollen cloth; but as the nature of the processes is in all cases the same, it will answer our purpose sufficiently if we give a sketch of the methods followed by the calico-printers.

There is a curious passage in Pliny's Natural History, from which it is evident that calico-printing in his time (the first century) was understood and practised in Egypt. The following is a translation of this passage.

"There exists in Egypt a wonderful method of dyeing. The white cloth is stained in various places, not with dye by the stuffs, but with substances which have the property of absorbing (fixing) colours. These applications are not visible upon the cloth; but when the pieces are dip into a hot caldron containing the dye, they are drawn out an instant after dyed. The remarkable circumstance is, that though there be only one dye in the vat, yet different colours appear on the cloth; nor can the colours be afterwards removed." It is evident enough that the substances employed to stain the cloth, as Pliny expresses it, were different mordants, which served to fix the dye upon the cloth. Thus if we suppose certain parts of a piece of cotton cloth to be impregnated with alumina, and the cloth afterwards dyed with madder, after the clearing, those parts only impregnated with the mordant would retain their red colour, while the remaining parts will continue white.

The general opinion is, that this ingenious art originated in India, and from that country made its way into Egypt. Whether this notion be well or ill founded, it is certain that calico-printing was known and executed by the Indians at a very early period. Their colours were beautiful and fast, and the varieties of pattern and the number of colours which they understood to fix on different parts of the cloth gave to their printed calicoes a beauty and a value of no ordinary kind; but their processes are so tedious and so clumsy that they could be put in practice only where labour was exceedingly cheap.

1 Plini Hist Nat. xxxv. 11. It is not more than a century and a half since calico-printing was transferred from India to Europe, and little more than a century since it became common in Great Britain. The nations with whom it has made the greatest progress are Switzerland; France, especially in Alsace; some parts of Germany; and Great Britain. In Europe the art has been in a great measure created anew. By the application of machinery, and by the light thrown on the processes by the improvements in chemistry, the tedious methods of the Indians have been wonderfully simplified; and the processes are remarkable for the rapidity with which they are executed, and for the beauty and fastness and variety of the colours which are applied on the surface of cotton and linen cloth.

We shall endeavour in this chapter to give a sketch of the different processes of calico-printing, such as they are at present practised by the most scientific printers in Lancashire, and in the neighbourhood of Glasgow.

The different processes to which the cotton cloth destined to be printed is subjected, are the following: singeing, bleaching, callendering, printing, stoving, duning, dyeing, brightening.

1. The singeing is intended to remove the fibres of cotton which protrude on the surface of the cloth. This is done by passing the cloth rapidly over the surface of a red-hot iron plate, which burns off all the hairs or protruding fibres of cotton without injuring the cloth. Of late years singeing has been effected by a very ingenious coal gas apparatus. But we need not dwell upon this preliminary process, because the singeing has been described already in this Encyclopedia under the article BLEACHING, to which we refer the reader.

2. The methods of bleaching and callendering cotton have been already given at sufficient length under the article BLEACHING.

3. There are two modes of printing; namely, block-printing and cylinder-printing. The former has been practised from time immemorial; the latter is a modern invention, and originated probably after the introduction of the art of printing into Great Britain. The figure intended to be communicated to the cloth is cut out upon a block of sycamore, the parts which are to make the impression being left prominent, and the rest of the block cut away, just as practised for wooden engravings. When the figure is too complicated, and the lines too fine, to admit of being cut in wood, it is made by means of small pieces of copper, which are very ingeniously driven into the block, and the intervals are filled up with felt. Great patience and ingenuity are displayed in making these blocks for use, and calico-printers are under the necessity of keeping a number of workmen at high wages for that express purpose.

The cylinder is a large circular copper plate, being a circular ruler, several feet long, and several inches in diameter, upon which the different figures to be given to the cloth are engraved; and by its circular motion the whole of these figures are impressed upon the cloth as it moves through under the cylinder. But the usual method of cylinder-printing is to have the intended figures engraven upon a flat copper plate about a square yard (or more) in size. Upon this plate the colour to be applied is spread. It is then pulled. As it passes along, an elastic steel plate called a doctor takes off all the colour except that which fills the engraving. It is then pressed against the white cloth, on which it thus leaves exactly the impression of the engraving. This is a very common method of printing pocket handkerchiefs.

Whether the printing is applied by the block, the cylinder, or by flat copper plates, the treatment of the goods is nearly the same.

Most commonly the printing process is applied to fixing mordants on the cloth, which is afterwards dyed in the common way, those parts only retaining the colour which have imbibed the mordant, while the other parts of the cloth remain white. Sometimes it is applied to cloth already dyed, in order to remove the colour from certain portions of it which are either intended to remain white, or to receive some other colour afterwards.

Sometimes it is applied to cloth before it is dyed blue, in order to prevent the indigo from being fixed on those parts to which it is applied, that they may remain white, or be afterwards made to receive other colours. Substances possessed of this property are called resist pastes.

Finally, it is frequently employed to communicate mordants and colouring matter at once to the cloth. Let us take a view of all these different uses.

I.—Mordants.

The principal mordants employed by the calico-printers are the following:

1. Alumina.—The usual aluminous mordant of the calico-printers is alum, partly decomposed by acetate of lime. The liquid is made by dissolving alum in water, and adding acetate of lime to the solution. The liquid has a specific gravity of 1-08, and contains about as much alum undecomposed as the liquid can hold in solution.

For particular purposes calico-printers make a mordant by mixing three parts of acetate of lead with four of alum. This mordant consists of a mixture of acetate of alumina and alum, for about a third part of the alum remains undecomposed.

When cloth to be dyed red is impregnated with this mordant, it is not thickened. When applied only to particular parts of the cloth by the block or the cylinder, it is thickened with flour or calcined starch, or gum senegal, according to the nature of the style of work.

2. Oxide of tin.—Perchloride of tin is very much used as a mordant. The colouring matter is previously mixed colours with it, and both are applied at once. Such applications what are called chemical colours. The mixture is allowed to dry on the cloth, which is then merely washed with water. Colours so applied are easily altered by light, soap, &c. Hence, in common language, a chemical colour means a fugitive colour. The colours produced in this way are, pink, from Brazil wood, peach wood, and cochineal; purple, from logwood; and yellow, with Persian berries.

Perchloride of tin is much used in another and pretty common process of the calico-printers, known technically by the appellation of steam colours. It is decomposed and converted into stannate of potash. The whole piece of cloth is immersed in the liquid containing the stannate of potash, and dried. The peroxide of tin is then precipitated upon the cloth, by immersing it into a solution of sal ammoniac or sulphate of magnesia, but most commonly into a very weak solution of free sulphuric acid. The different colouring matters previously thickened with starch are then printed on the cloth, and the whole subjected to the action of steam. The consequence is, that by the joint action of moisture and heat, a combination takes place between the colouring matter and the oxide, which is thus rendered insoluble; and no considerable quantity of water is ever present to carry off the colouring matter before it has combined with the mordant.

In this way pink, purple, and yellow are obtained of every variety of shade that can be produced by mixture of these colours with each other, or with Prussian blue.

3. Peroxide of iron.—This metallic oxide is much used as a mordant. It is employed in the state of acetated protoxide of iron, by dissolving metallic iron in pyrolignic acid. In a few days after being applied to the cloth, especially if exposed to a moist atmosphere, it loses its acid, and the iron becomes peroxidized.

Acetate of iron, of specific gravity 1-05, gives a black with madder. Various shades of purple are obtained by adding different proportions of the mordant and dyestuff. Various shades of red, from brown red to pink, are obtained in the same way, substituting the aluminous mordant of various strengths for the iron. Chocolates are got by mixing the aluminous and iron mordants, and then dyeing with madder.

These are the principal mordants employed by the calico-printers. Several substances have so strong an affinity for the cloth that they require no mordant. This is the case with indigo, sesquioxide of manganese, peroxide of iron, and chromate and dichromate of lead.

II.—Substances used for discharging Colours.

Most colours are fixed in the cloth, either by means of mordants or by being in a particular state of oxidization. Thus madder is fixed by means of alumina, and cochineal by means of oxide of tin. Sesquioxide of manganese loses its fixity and is washed away by water the moment that it is converted into protoxide. Hence, when the printers wish to discharge a colour from cloth, they employ something that will dissolve the mordant, or, if no mordant be present, will de-oxidize the colouring matter, which in that case is a metallic oxide. The dischargers, then, are either acids, or substances having a strong affinity for oxygen. We shall point out the chief of these, and the way of applying them.

Method of using:

1. Citric acid is much used by printers to dissolve alumina and peroxide of iron, and thus to prevent the colours which these mordants would fix from remaining on the cloth. It is obtained by evaporating lemon juice, and thickening it with gum-senegal for the cylinder, or with gum and pipe-clay for the block. It is occasionally assisted by bisulphate of potash or sulphuric acid.

Sometimes the citric acid is printed on white cloth, and the aluminous or iron mordant slightly thickened and dried immediately, to prevent the swelling of the acid figures. At other times the mordants are first applied, and the acids printed over them.

In both cases the goods are afterwards passed through hot water containing cow's dung, and well washed before drying. By this means all the mordant is removed from those parts on which the acid was applied, which of course remains white when the cloth is dyed.

2. Tartaric acid thickened with gum is applied by the block or cylinder to cloth previously dyed Turkey red. It is then passed through an aqueous solution of bleaching powder. The acid disengaging the chlorine, the red colour is discharged from those places to which it had been applied, while all the other parts of the cloth retain their red colour.

When oxide of lead is deposited on the cloth along with the acid, and the cloth, after passing through the aqueous solution of bleaching powder, is made to pass through water impregnated with bichromate of potash, the parts which would otherwise have become white are changed into a fine yellow. This beautiful process is not confined to Turkey red.

3. Protchloride of iron is used to discharge the manganese brown and substitute a buff. This it does by depriving the manganese of its oxygen, and thus rendering it soluble; while the protchloride of iron converted into perchloride deposits peroxide of iron on the cloth, which combines and produces the characteristic buff or orange Print colour of that oxide.

Protchloride of iron is used in a variety of ways. It deoxidizes indigo in the indigo vat, and renders it soluble in lime water. It produces gold, buff, &c., colours, and makes a good chemical black with logwood.

4. Protchloride of tin, when applied to cloth dyed brown by sesquioxide of manganese, immediately reduces it to the state of protoxide, and thus discharges the colour and leaves the parts white. If it be mixed with Brazil wood or cochineal, it discharges the manganese as before, but leaves a pink. When mixed with logwood it leaves a purple, and when with Prussian blue, a blue.

To produce a yellow upon manganese, ground chloride of tin is mixed with sulphate of lead. The mixture thickened with calcined starch is printed on the manganese brown. As soon as it is dry, the manganese being reduced to the state of protoxide, may be washed off; but the sulphate of lead adheres to the cloth, from an affinity which exists between them. The cloth being now passed through a solution of bichromate of potash, those parts containing the sulphate of lead are dyed a beautiful yellow by the formation of chromate of lead.

Chloride of tin is capable also of removing peroxide of iron from cloth, by reducing it to protoxide, as it does the sesquioxide of manganese. For this purpose it is printed on a deep colour, composed of peroxide of iron and quercitron yellow. The protchloride of iron is formed and washed away, while the oxide of tin remaining, constitutes a mordant for the quercitron. And thus the parts to which the protchloride of tin was applied become yellow.

The protchloride of tin is also employed occasionally to discharge the orange, consisting of dichromate of lead fixed upon cloth. This it does by reducing the chromic acid to protoxide. As the green oxide of chrome still continues attached to the cloth, the discharged parts do not assume a good white colour. But this does not much affect the blue and purple colours substituted for the orange, by mixing the protchloride of tin with Prussian blue or with logwood.

When protchloride of tin is decomposed by carbonate of soda, protoxide of tin is obtained. This protoxide is used along with potash to render indigo soluble. The protoxide de-oxidizes the indigo, and the potash dissolves the yellow base. It is then applied to the cloth in the way that will be explained afterwards.

III.—Resist Pastes.

These pastes are substances which have the property of restoring the blue colour to dissolved indigo, and thus of preventing it from being fixed to those parts of the cloth on which the resist pastes have been applied. Any substance which has the property of parting with oxygen readily answers this purpose. Thus sulphate of copper, or any salt containing black oxide of copper, when put into the indigo vat, instantly revives the indigo, by communicating oxygen to it. The hydrated black oxide has the same effect, and so have the sesquioxide and the dioxide of manganese.

The calico-printer's indigo vat is a very deep large vessel filled with water, into which indigo, sulphate of iron, resist and an excess of lime are put. The lime decomposes the paste-sulphate of iron, and the protoxide of iron thus disengaged coming in contact with the indigo at the bottom of the

---

1 An impure acetic acid, obtained by distilling wood. vat, deprives it of an atom of oxygen, and thus renders it capable of combining with the lime, and of forming a compound which dissolves in water and forms a yellowish-coloured solution. Where this solution is in contact with the atmosphere the indigo is revived, assumes its blue colour, and loses its solubility. Hence the blue scum which always covers the surface; but this scum in some measure protects the rest of the vat. When cloth is dipped into this vat it comes out yellow; but the indigo, from its exposure to the air, gradually absorbs oxygen, so that the cloth becomes at first green, and finally blue. But if to any parts of the cloth before dipping something has been applied which has the property of giving out oxygen to the indigo, all the indigo which would have been imbibed by these parts has been revived before it has had time to come in contact with the cloth; and in the blue state it has not the property of uniting with the cloth, but may be easily washed off. Hence the parts to which the resist pastes, as they are called, have been applied, remain white. The principal resist pastes are the following:

1. Blue paste, or vitriol paste, consists of a mixture of sulphate and acetate of copper, and the solution is thickened with gum-senegal and pipe-clay for the block, and with flour for the cylinder. When the cloth on which this paste has been printed is dipped into the indigo vat, the indigo is oxidized before it reaches the surface of the cloth. After dyeing, the piece is passed through weak sulphuric acid, to remove the oxide of copper which has been precipitated.

2. Mild paste consists of sulphate of zinc, gum, and pipe-clay. It is used along with other colours which copper would injure, or which would be destroyed by immersion in sulphuric acid. It resists a pale blue, and the removal of the oxide of zinc afterwards by an acid is not necessary, as when copper is employed.

Sulphate of zinc, as well as all the other metallic salts, and all the acids, precipitate indigo from its solution in lime. It does not revive indigo like the salts of copper; but when the base of indigo is precipitated, it is not so readily fixed as when in a state of solution. The oxide of zinc, with the gum and pipe-clay, act mechanically in keeping it at a distance.

3. Red paste consists of the aluminous mordant already described, mixed with acetate of copper, gum, and pipe-clay. It resists pale blues; and the alumina remains upon the portions which are white, to be afterwards dyed with madder and produce a red, or with quercitron for a yellow.

4. Neutral paste is the name given by calico-printers to a compound of lime juice, sulphate of copper, gum, and pipe-clay. It resists during a short dip in the blue vat; and the lime juice gives it the property of remaining white when the piece is dyed in madder, even where the preceding aluminous paste goes over it. This acid also prevents the lime of the blue vat from precipitating copper upon the cloth, which would give the cloth a deep-brown tinge in the madder vessel.

5. Chrome yellow resist paste consists of a mixture of a salt of copper to resist the blue vat, with a salt of lead to produce a yellow with bichromate of potash after having been dyed blue in the blue vat.

These five constitute the principal resist pastes. There are indeed a few others, but they are of little importance, and they will easily suggest themselves to those who understand the principles of chemistry.

Instead of describing the mode of printing mordants and colouring matters at once, or of applying chemical colours, as they are called, we think it will be better to make a few observations on each particular colour in succession, without minding whether it be applied by dyeing or printing.

1. Red.

The usual dyestuff for red among the calico-printers is madder. Goods which have received the aluminous mordant applied in figures either by the cylinder or the block, are first passed through hot water containing cow-dung, and well washed. They are then put into a dye vessel along with madder and cold water, to which heat is gradually applied either by means of steam or fire. The pieces are kept constantly moving in the vessel till they have gained the requisite depth of shade, when they are taken out and washed again. The colour given by the madder to those parts of the cloth which have received no mordant, is removed by boiling the cloth in water containing either bran or soap, both of which substances have the property of removing it without injury to the red figure. Afterwards the white portion of the cloth is further improved by rinsing it in a weak warm solution of bleaching powder.

When Brazil wood or peach wood is used instead of madder, the mordant and method of dyeing are the same. The cloth, however, does not bear the same treatment after dyeing, and does not require it, because these colours are much more easily removed from the parts of the cloth destitute of mordant.

2. Pink.

The most beautiful pink to be seen on calico is given by means of cochineal. The mordant is alumina, and the method of proceeding similar to that already described. Madder, when mixed with bran to remove the brown colouring matter, gives what is called a brown pink.

Safflower cannot be applied to cloth in figures, but it is frequently employed for giving a uniform pink dye to pieces of cloth. It is first steeped in water containing a carbonated alkali, which dissolves its colouring matter. The solution freed from the fibrous part of the dyestuff is then saturated by an acid, which is commonly lime juice. A piece of cloth immersed in this saturated solution extracts the pink colouring matter from it, which is afterwards heightened by immersion in weak cream of tartar. By this means a very beautiful but fugitive colour is communicated.

3. Yellow.

The most usual substance now employed by the calico-printers for communicating this colour is chromate of lead. The use of this very beautiful and fixed colour does not go farther back than ten or twelve years. The writer of this article endeavoured about fourteen years ago to prevail upon some of the calico-printers in the neighbourhood of Glasgow to try it, but unsuccessfully. At last, after much entreaty, Mr Ramsay, at that time an extensive manufacturer of colours for calico-printers, was induced to make a small quantity of bichromate of potash, so as to put it in the power of those who chose it to try how it would answer. Soon afterwards the use of it was introduced into some of the printing works of France. From that country it soon made its way to Lancashire, and thence to Glasgow. The bichromate of potash, when first prepared, sold as high as a guinea per pound. Of late years it has been as low as tenpence. The method of using this beautiful dyestuff is this:

Acetate or nitrate of lead is applied to the cloth, either by means of the block or cylinder. The cloth is either immediately passed through a solution of bichromate of potash, or the oxide of lead is in the first place set free from its acid by immersing the cloth in lime water, or in some cases into an aqueous solution of bleaching powder. Indeed the processes for applying chromic acid are varied in a great many ways, to suit the different colours which are applied along with the yellow; as in the yellow discharge for bronze, and the yellow resist on blue already described, the yellow discharge on Turkey red, &c. &c.

Quercitron bark is also often employed to communicate a yellow by the calico-printers. The alumina mordant is first applied, and the cloth is cleaned in the dung vessel in the way described when giving an account of madder dyeing. Quercitron bark gives out its colouring matter at a lower heat than madder; and the parts of the cloth to which no mordant has been applied remain tolerably white after the cloth has been washed in cold water.

A decoction of Persian berries constitutes likewise a common yellow dyestuff for calico-printers. The decoction is mixed with the requisite portion of alum to act as a mordant; but a combination between the alumina and the yellow colouring matter takes place without the intervention of a third agent. It is effected either by exposing the cloth to the action of steam, or by putting the piece into water containing an alkali or its carbonate.

4. Blue.

The usual dyestuffs for giving a blue colour to calicoes are indigo and Prussian blue.

The method of forming the indigo vat has been already mentioned. The cloth is dipped in the clear solution. When taken out it is yellow, and gradually becomes blue by absorbing oxygen from the atmosphere. If a deep shade is wanted, the cloth is immersed again, when it receives an additional quantity of indigo, which must be oxidized, as the former was, by exposure to the air. These alternate dips and airings are repeated till the requisite shade is attained.

What is called pencil blue, is a solution of indigo in caustic potash or soda, the indigo being de-oxidized by means of orpiment. The solution is thickened by means of British gum, or gum-senegal, and printed upon the cloth either by the block or cylinder. When upon the cloth, the indigo attracts oxygen from the air, and thus becomes blue and fixed. The gum, alkali, loose indigo, &c. are washed away in water.

Prussian blue may be applied to cloth in various ways. We shall mention some of the principal of these.

1. An iron mordant is first applied to the cloth, and allowed to remain untouched till the iron has had time to be peroxidized, and in that way become fixed. The piece is then cleaned as for dyeing, and dip into a solution of prussiate of potash mixed with sulphuric acid, to disengage the acid or cyanogen which it contains.

2. Prussian blue is dissolved in muriatic acid, oxalic acid, perchloride of tin, or nitrate of iron, and the solution applied immediately to the cloth in the usual way.

3. Ferrocyanic acid is printed upon the cloth, and decomposed by means of a steam heat, hydrocyanic acid escapes, and cyanodide of iron remains in the cloth. It becomes blue by exposure to the air, or by being put into a weak solution of bleaching powder, or of bichromate of potash.

Logwood forms a bluish compound with the salts of copper; but this colour is exceedingly fugitive, and the use of it has been long laid aside.

5. Black.

Various methods are employed by the calico-printers to produce a black upon cotton. An iron mordant of the specific gravity 1·05 gives a black with madder. The common alumious mordant gives a black when cloth impregnated with it is dyed in logwood. A chemical black is made from a decoction of nutgalls mixed with nitrate of iron. Another chemical black is formed by mixing a decoction of logwood with a solution of sulphate of iron.

If cloth be dyed successively blue, red, and yellow, it becomes black.

6. Buff.

To produce this colour, the cloth is printed with a mixture of sulphate and acetate of iron. After having had time to be partly peroxidized and partially decomposed, it is washed in water; or if a stronger buff is wanted, it is rinsed in cream of lime till the protoxide is converted into the red. No mordant is required, as the peroxide of iron has a strong affinity for cotton cloth.

7. Gold.

For this colour the process is the same as for buff. The only difference is, that the solution is stronger.

8. Orange.

The most beautiful orange is given by means of dichromate of lead. It is obtained by saturating bichromate of potash with potash or lime, and immersing in it while hot, cloth printed with a salt of lead. Nitric acid changes this orange into yellow, by uniting with half the oxide of lead.

9. Green.

The fast green, discovered by Mr James Thomson of Primrosehill, near Clitheroe, and commonly known by the name of Warneck's green, is a mixture of the pencil blue already described, and aluminated potash. The mixture is thickened and applied as the blue is. The alumina is then precipitated from its alkaline solution by being passed through a weak solution of sal ammoniac or sulphate of magnesia. The cloth is then dyed yellow in quercitron bark. It is sufficiently known that the two colours blue and yellow form a green.

Carbonate of copper makes a poor faint green upon cloth, while the hydrated black oxide forms a bright blue. It is obtained by printing on a strong solution of copper, and dipping the cloth, when dry, into strong caustic potash or soda.

The colour called Scheele's green is a mixture of arsenite of copper and the hydrated black oxide. It is obtained by printing on the cloth a strong solution of copper thickened with gum, and then dipping it into a mixture of arsenite of potash and caustic potash. Hot water destroys this colour, by depriving the oxide of copper of its water.

A green is obtained from Prussian blue and yellow berries, by mixing together ferrocyanic acid, yellow berries, and an alumious mordant, and subjecting them to the action of steam.

Various other greens are attained by printing yellows over blues previously produced.

Saxon green is produced by printing a solution of cerulin over a yellow formed by dyeing the alumious mordant with quercitron bark or weld. The cerulin adheres to those parts of the cloth which have been dyed yellow, but very slightly to the white cloth, from which it is easily washed away.

10. Lilac.

This colour is communicated to cloth by printing on a much diluted mixture of the iron and alumious mordants thickened with gum-senegal. The cloth is then dyed in madder exactly as described for producing a red. 11. Chocolate.

The same mordants, but much stronger, and dyeing in madder in the same way, produces this colour.

12. Purple.

The iron mordant, diluted to the shade required, is printed on the cloth, which is then dyed in madder in the usual way.

When the cloth, after a weak aluminous mordant has been printed on it, is dyed in logwood, a purple colour is obtained.

13. Brown.

By far the finest and most fixed brown is communicated to cotton by means of the sesquioxide of manganese. The process is rather a recent one, but of late years it has become very general. A neutral solution of sulphate of manganese is thickened with gum, and printed on the cloth. It is then dipped into rather strong caustic potash ley, which precipitates the protoxide of manganese. By exposure to the air, or by immersion in bleaching powder solution, or in bichromate of potash, this protoxide absorbs more oxygen, and becomes fixed on the cloth. Though the state of oxidization has not been determined by experiment, yet it is probable that the manganese is in the state of red oxide, which is a compound of two atoms sesquioxide and one atom protoxide.

14. Drah.

This is made by printing on an iron mordant, and then dyeing in quercitron bark.

15. Olive.

Formed by printing on a mixture of the iron and aluminous mordants, and dyeing in quercitron bark.

16. Dove.

A weak iron mordant dyed in cochineal.

17. Slate.

A weak iron mordant dyed in nutgalls or in sumach.

18. Cinnamon.

The aluminous mordant, with the addition of a little iron, dyed in a mixture of madder and quercitron bark.

Such are the principal colours given to calicoes, and such are the methods of applying and fixing them.

We have now finished our account of calico-printing; for the duning and brightening processes have been described while treating of the various colours; and the storing, which consists simply in drying the goods in a room raised by artificial heat to a temperature higher than the boiling point of water, requires no description.