removed, they are put into a pit of water impregnated with pigeon dung, called a grainer, forming an alkaline ley, which in a week or ten days soaking out the lime, grease, and saponaceous matter (during which period they are several times scraped over with a crooked knife, to work out the dirt and filth), softens the skins, and prepares them for the reception of the ooze. They are then put into a pit of weak ooze, in the same manner as the hides, and being frequently handled, are by degrees removed into a stronger, and still stronger liquor, for a month or six weeks, when they are put into a very strong ooze, with fresh bark ground very fine, and at the end of two or three months, according to their substances, are sufficiently tanned: when they are taken out, hung on poles, dried, and are fit for sale. These skins are afterwards dressed and blacked by the curriers, and are used for the upper leathers of shoes, boots, &c.

The lighter sort of hides, called dressing hides, as well as horse hides, are managed nearly in the same manner as skins; and are used for coachwork, harness work, &c.

As the method of tanning above described, and all others in general use, are extremely tedious and expensive in their operation, various schemes at different times have been suggested to shorten the process, and lessen the expence.

Much light has been thrown by modern chemists upon the theory of tanning, though it does not appear that any considerable improvements have been made in the practice of this art. M. Seguin, in France, has particularly distinguished himself by his researches on this subject, and much improved the art in his country.

In 1795, Mr. William Desmond obtained a patent for practising Seguin's method in England. He obtained the tanning principle, by digesting oak bark or other proper material in cold water, in an apparatus nearly similar to that used in the saltpetre works. That is to say, the water which has remained upon the powdered bark for a certain time, in one vessel, is drawn off by a cock, and poured upon fresh tan. This is again to be drawn off, and poured upon other fresh tan; and in this way the process is to be continued to the fifth vessel. The liquor is then highly coloured, and marks from six to eight degrees upon the hydrometer for salts. This he calls the tanning lixivium.

The criterion for ascertaining its strength is the quantity of the solution of gelatine which a given quantity of it will precipitate. Isinglass is used for this purpose, being entirely composed of gelatine. And here it may be observed, that this is the mode of ascertaining the quantity of tanning principle in any vegetable substance, and consequently how far they may be used as a substitute for oak bark.

The hides, after being prepared in the usual way, are immersed for some hours in a weak tanning lixivium of only one or two degrees; to obtain which, the latter portions of the infusions are set apart, or else some of that which has been partly exhausted by use in tanning. The hides are then to be put into a stronger lixivium, where, in a few days, they will be brought to the same degree of saturation with the liquor in which they are immersed. The strength of the liquor will by this means be considerably diminished, and must therefore be renewed. When the hides are by this means completely saturated, that is to say, perfectly tanned, they are to be removed, and slowly dried in the shade.

It has been proposed to use the residuum of the tanning lixivium, or the exhausted ooze (which contains a portion of gallic acid, this forming a constituent part of astringent vegetables), for the purpose of taking off the hair; but this liquor seems to contain no substances capable of acting upon the epidermis, or of loosening the hair; and when skin is depilated by being exposed to it, the effect must really be owing to incipient putrefaction.

The length of time necessary to tan leather completely, according to the old process, is certainly a very great inconvenience; and there is no doubt but that it may be much shortened by following the new method. It has been found, however, that the leather so tanned has not been so durable as that which has been formed by a slower process.

The public is much indebted to Sir Humphrey Davy, professor of chemistry in the Royal Institution, for the attention which he has paid to this subject. From his excellent paper "On the Constituent Parts of Astringent Vegetables," in the Philosophical Transactions, we present the reader with the following extract.

"In considering the relation of the different facts that have been detailed, to the processes of tanning and of leather-making, it will appear sufficiently evident, that when skin is tanned in astringent infusions that contain, as well as tanning, extractive matters, portions of these matters enter, with the tanning, into chemical combination with the skin. In no case is there any reason to believe that gallic acid is absorbed in this process; and M. Seguin's ingenious theory, of the agency of this substance, in producing the de-oxygenation of skin, seems supported by no proofs. Even in the formation of glue from skin, there is no evidence which ought to induce us to suppose that it loses a portion of oxygen; and the effect appears to be owing merely to the separation of the gelatine, from the small quantity of albumen with which it was combined in the organized form, by the solvent powers of water.

"The different qualities of leather made with the same kind of skin, seem to depend very much upon the different quantities of extractive matter it contains, The leather obtained by means of infusions of galls is generally found harder, and more liable to crack, than the leather obtained from the infusion of barks; and in all cases it contains a much larger proportion of tanning, and a smaller proportion of extractive

matter.

"When ekin is very slowly tanned in weak solutions of the barks, or of catechu, it combines with a considerable proportion of extractive matter; and in these cases, though the increase of weight of the skin is comparatively small, yet it is rendered perfectly insoluble in water, and is found soft, and at the same time strong. The saturated astringent infusions of barks contain much less extractive matter, in proportion to their tanning, than the weak infusions; and when skin is quickly tanned in them, common experience shews that it produces leather less durable than the leather slowly formed.

"Besides, in the case of quick tanning by means of infusions of barks, a quantity of vegetable extractive matter is lost to the manufacturer, which might have been made to enter into the composition of his leather. These observations shew that there is some foundation for the vulgar opinion of workmen, concerning what is technically called the

feeding of leather in the slow method of tanning; and though the processes of the art may, in some cases, be protracted for an unnecessary length of time, yet in general they appear to have arrived, in consequence of repeated practical experiments, at a degree of perfection which cannot be very far extended by means of any elucidations of theory that have as yet been known."

As a vast quantity of bark may easily be obtained in countries that are covered with natural forests, such as many parts of America, New Holland, &c. it has been suggested, as a method of lessening the expense of freight in bringing it over, to make an extract from the bark, which might be very easily transported, and which would serve purpose of the tanner as well as the bark itself.

the

It was first suspected by Sir Joseph Banks, and afterwards confirmed by the experiments of Professor Davy, that a substance called catechu or terra Japonica, brought from the East Indies, contained a vast quantity of tannin; so much so, that it far excels every other known substance in this respect. One pound of catechu contains as much tannin as eight or ten pounds of common oak bark, and would consequently tan proportionately as much more leather. It is an extract made from the wood of a species of mimosa, by decoction and subsequent evaporation.

Oak bark being a very expensive article in the process of tanning, various substances have been proposed as substitutes for it. All the parts of vegetables which are of an astringent nature, contain tannin (which may be known by their giving precipitates with gelatine, insoluble in water), and will answer this purpose. The leaves, branches, fruit, flowers, of a vast number of plants; every part of the oak, as the leaves and acorns, oak saw-dust, and the bark of almost all trees, contain more or less tannin.

Mr. Biggins has made a great many experiments upon the quantity of tanning principle in various barks from which he has constructed the following table:

Currying. The art of currying consists in rendering tanned skins supple and of uniform density, and impregnating them with oil, so as to render them in a great degree impervious to water.

The stronger and thicker hides are usually employed for making the soles of boots and shoes, and these are rendered fit for their several purposes by the shoemakers after they are tanned; but such skins as are intended for the upper leathers and quarters of shoes, for the legs of boots, for coach and harness leather, saddles, and other things, must be subjected to the process of currying.

These skins after coming from the tanners, having many fleshy fibres on them, are well soaked in common water. They are then taken out, and stretched upon a very even wooden horse; where with a paring knife all the superfluous flesh is scraped off, and they are again put in to soak. After the soaking is completed, the currier takes them again out of the water, and having stretched them out, presses them with his feet, or a flat stone fixed in a handle, to make them more supple, and to press out all the filth that the leather may have acquired in tanning, and also the water it has absorbed in soaking.

The skins are next to be oiled, to render them pliant and impervious to wet. After they are half dried, they are laid upon tables, and first the grain side of the leather is rubbed over with a mixture of fish-oil and tallow; then the flesh side is impregnated with a large proportion of oil. After having been hung up a sufficient time to dry, they are taken down and rubbed, pressed, and folded in various directions, and then spread out, when they are rolled with considerable pressure upon both sides with a fluted board, fastened to the operator's hand by a strap; by this means, and by repeating the rolling, a grain is given to the leather.

After the skins are curried, it may be required to colour them: the colours usually given to them are black, red, green, yellow, &c.

If the skins are to be blacked, the process varies according to the side of the skin to be coloured. Leather that is to be blacked on the flesh side, which is the case with most of the finer leathers intended for shoes and boots, is coloured with a mixture of lamp black, oil, and tallow, rubbed into the leather. And what is to be coloured on the grain side is done over with chamber-ley, and then with a solution of sulphate of iron (green copperas), which turns it black.

CHAP. XI.

JAPANNING.

JAPANNING is properly the art of varnishing and painting ornaments on wood, in the same manner as is done by the natives of Japan in the East Indies.

The substances which admit of being japanned are almost every kind that are dry and rigid, or not too flexible, as wood, metals, leather, and paper prepared.

Wood and metals do not require any other preparation, but to have their surfaces perfectly even and clean; but leather should be securely strained, either on frames or on boards; as its bending, or forming folds, would otherwise crack and force off the coats of varnish. Paper should be treated in the same manner, and have a previous strong coat of some kind of size; but it is rarely made the subject of japanning till it is converted into papier machie, or wrought by other means into such form, that its original state, particularly with respect to flexibility, is changed.

One principal variation from the method formerly used in japanning is, the omitting any priming or undercoat on the work to be japanned. In the older practice, such a priming was always used; the use of which was to save in the quantity of varnish, by filling up the inequa lities in the surface of the substance to be varnished. But there is a great inconvenience arising from the use of it, that the japanned coats are constantly liable to be cracked, and peeled off, by any violence, and will not endure near so long as the articles which are japanned without any such priming.

The French still retain the use of this undercoat; and their japanned goods are upon that account less durable than those manufactured at Birmingham, where it is not used.

Of the Nature of Japanned Grounds.-When a priming is used, the work should first be prepared by being well smoothed with fish-skin or glass-paper, and being made thoroughly clean, should be brushed over once or twice with hot size, diluted with two-thirds water, if it is of the common strength. The priming should then be laid on as even as possible, and should be formed of a size of a consistency between the common kind and glue, mixed with as much whiting as well give it a sufficient body of colour to hide the surface of whatever it is laid upon, but not more. This must be repeated till the inequalities are completely filled up, and then the work must be cleaned off with Dutch rushes, and polished with a wet rag.

When wood or leather is to be japanned, and no priming is used, the best preparation is to lay two or three coats of coarse varnish, composed in the following manner:

Take of rectified spirits of wine one pint, and of coarse seed-lac and resin each two ounces; dissolve the seed-lac and resin in the spirit, and then strain off the varnish.

This varnish, as well as all others formed of spirits of wine, must be laid on in a warm place; and, if it can be conveniently managed, the piece of work to be varnished should be made warm likewise; and,