Tanning
The following is the French mode of tanning all kinds of leather in a short time, highly important to the manufacturers of leather in this country, as it points out a secure and profitable mode of turning their capital twelve or thirteen times in a year, instead of once.
Washing Hides.
The best method of washing hides is to stretch them in a frame, and place them, thus stretched, in running water. If running water cannot be conveniently had, still water can be made to answer by frequent stirrings and agitations; the remainder of the operation of cleansing is performed as in the common way.
On taking off the Hair.
Begin by shaking some lime in a pit, to which put a great quantity of water, then stir this water well, that it may become saturated with the lime, then place your hides in the pit perpendicularly; for this purpose, several wooden poles should be fixed across the pit; to these poles the hides are to be fastened with strings at proper distances, each hide being first cut in two; whilst the hides were thus placed in the lime water, the lime itself, which had deposited on the bottom of the pit, was frequently stirred up to increase the strength of the water, and to make it more operative; the hair thus treated, will, in about eight days, come off the hide with great ease. A shorter and a better method may effect this purpose in two days; that is, to plunge the hides, after being washed and cleaned, into a solution of tan, which (having been already used) contains no longer any of the tanning principle, mixed with a five hundredth, or even a thousandth part of the oil of vitriol, commonly called sulphuric acid; this operation not only takes off the hair, but raises and swells the hide; as, in the old way, is generally effected by barley sourings. However, further swelling and raising is necessary, and the hides should again be plunged in another quantity of spent tan-water mixed with the one thousandth part of the oil of vitriol, and thus steeped a second time; their swelling and raising will be completed in about forty-eight hours; after this operation the hides will acquire a yellow colour, even to the interior part of their substance. To determine if the swelling and raising be sufficiently completed, let one of the corners of the hide be cut, and if it is in a proper state there will not appear any white streak in the middle, but the hide throughout its whole substance will have acquired a yellow colour, and semi-transparent appearance. Mr. S—— is of opinion, that swelling and raising hides is not necessary, and that the hides tanned without this operation are less permeable to water. On tanning on the new principle, as practised by Mr. S——, he places several rows of casks on stillings sufficiently elevated above the ground to place a can or tub under them; these casks were filled with fresh finely ground tan, then a certain quantity of water was poured into the first of them, which water, as it ran through the tan, exhausted and carried off the soluble part, and as fast as it ran into the vessels below, was taken away and poured on the second cask, and so on successively until the solution was sufficiently saturated, and thus it may have been brought to ten or twelve degrees of the arometer for salts. In order to exhaust the tan of the first cask, Mr. S—— continued pouring water on the first cask until it ran off clear; at which time the tan was deprived of its soluble part; these liquors, as it may be easily conceived, were carefully kept for future operations; large wooden vats are considered the best sort of vessels for holding this solution, as well as for making and preparing it; hogsheads, on a small scale, may be made to answer. It is particularly in the use of this solution that Mr. S——’s method consists; the quickness with which the solution acts is truly astonishing, and when we see it, there is cause of surprise in thinking why it was not found out before. As soon as the hides are taken out of the water, impregnated with sulphuric acid, Mr. S—— puts them into a weak solution of tan, in which he leaves them for the space of one or two hours; he afterwards plunges them into other solutions of tan, more or less charged with the tanning principle, in proportion to their strength, so that in the experiments at which we were present, some heavy hides were tanned in six or eight days, others in twenty and twenty-five days. In placing the hides in the solutions, some precautions are necessary; the hides should be suspended on a wheel, or in a frame where they should be stretched, and placed one inch apart, so as to admit the solution freely about them; Mr. S—— recommends cutting off the head and the neck of the hide, and a slip down each side, in which slip the feet and belly part are to be comprehended; and the circumstance which determines Mr. S—— to cut the hide in this manner is, that the feet, and the parts that are near the belly, are more spongy and more easily penetrated by the tan; and as they produce leather of an inferior quality they may be more advantageously tanned separately, than put promiscuously into the solutions of tan with the rest. The remaining part of the hide is to be divided into two or more parts or pieces, so as to be easily placed in the vats or casks.
Drying the Hides.
The hides, when taken out of the solution of tan, must be dried with the usual precautions, that is to say, so slowly, that the skin does not shrink on the flesh side. With respect to thinner hides, for the upper leather of shoes, Mr. S—— begins by washing and taking off the flesh in the manner already described, or, as is done in the common way for strong soal leather; he then takes off the hair by means of clear lime-water; he does not make them undergo the operation of swelling, but puts them immediately into weak solutions of tan, the strength of which he gradually increases, but without ever bringing it to the degree of contraction, which he gives it when it is to be used in tanning thick leather; two, three, or four days, are enough for tanning the thinner kind of leather. Leather which is not sufficiently impregnated with the tanning principle, is generally known by a white speck or streak, which is observable in the middle of its substance. We can affirm that those hides which were tanned in our presence, in a few days, were completely tanned, as the above mentioned white streak was not perceivable; we may also add, that Mr. S——’s method has the advantage of affording the opportunity of observing and examining, from time to time, the progress of the operation; for this purpose nothing more is necessary but to take a slip off the hide out of the vat, and cut off a corner of it, the white streak already spoken of will appear more or less thick, until the tanning is completed; it has been generally supposed, that the tan in the tanpits had no other effect upon the leather than that of hardening and bracing the fibres of the skin, which has been relaxed by the preliminary of tanning. Mr. S——, however, examined the operation more closely, and discovered that there existed in the tan a principle which was soluble in water, by which the tanning was brought about. That this principle afterwards became fixed in the leather in consequence of a particular combination between the said principle and the skin; and this combination produced a substance that was not soluble in water; all this has been demonstrated by Mr. S——, in the most evident manner. It is well known that if leather, which has not been tanned, is boiled in water, it is in a short time almost entirely dissolved therein. This solution, by being concentrated, produces a jelly, or size, which, by farther evaporation, and being dried in the air, becomes what is called glue. Mr. S—— having, in the course of his experiments, examined the effects of a solution of tan upon a solution of glue, observed that they were hardly mixed together before a white felamentous precipitate took place, owing to a combination of the glue with the tanning principle contained in the solution of tan. This precipitate is insoluble in water, either hot or cold, and acquires colour by being exposed to the light. The foregoing experiment furnishes a true explanation of the process of tanning; for it will easily be conceived that the solution of tan acts upon the hides (from which glue is produced) in the same manner as it acts upon glue; this is what really happens in common tanpits, and Mr. S——’s new method, in which the solution of tan gradually penetrates the hides, and as it penetrates combines with it, producing a gradual change of colour that is very observable, till at last the colour of the hide is changed throughout, and it acquires a compact texture and marbled appearance, like that of a nutmeg: by this it plainly appears, that a precipitation also takes place in the action of tanning, although the hide is not dissolved, but merely swelled so as to enable the solution to penetrate it more easily. The property which animal jelly, or glue, possesses, of being precipitated by a solution of the tanning principle, furnishes a means of discovering what substances may be useful in tanning: nothing more is necessary than to make a solution or infusion of the vegetable substance supposed proper for that purpose, and that upon being mixed with a solution of glue, will show by the greater or less quantity of precipitate produced, what probability there is that such substance might be advantageously employed in tanning.
Another Remark.
Lime-water also offers an excellent means of discovering such substances. If lime-water be added to a solution of tan, the mixture instantly produces a copious precipitate; and if a sufficient quantity of lime-water be added to neutralize the whole of the tanning principle, then the supernatant liquor, although still possessing colour, will not form any precipitate with glue; I mean in solution. In like manner the liquor separated from a precipitation, caused by the mixture of a solution of tan with one of glue, will not produce any precipitate with lime-water, if, during the precipitation, the tanning principle has been completely neutralized. This shows evidently that Doctor M’Bride’s method of exhausting the tan by means of lime-water is defective, and that by so doing a loss of the tanning principle takes place, in proportion to the quantity of it contained or combined with the lime dissolved in the lime-water.
Another Remark.
As in summer the solution of tan is disposed to run into the vinous fermentation, and, of course, from that into the acetous, and have its principal changed, no more of the solution of tan should be prepared in the summer season than is wanted for immediate use. In winter, this precaution in not necessary, as in that season it will keep, and may be then prepared for exportation to any part of Europe and thus converted into a profitable article of commerce.
A table showing the time different hides took to be completed, in the operations of preparing and tanning.
Ten ox hides, taken the 17th of August, were completely tanned by the 6th of September, in all, twenty days.
| Washing the hides, | 2 days. |
| Taking off the hair, | 5 do. |
| Raising or swelling, | 5 do. |
| Second washing, | 2 do. |
| Tanning, (properly so called,) | 6 do. |
| 20 days. |
Ten ox hides, taken the 19th of July, were tanned the 9th of August, making twenty-one days.
| Washing, | 2 days. |
| Taking off the hair, | 10 do. |
| Swelling, | 1 do. |
| Tanning, | 8 do. |
| 21 days. |
One ox hide, taken the 3d of September, was tanned the 2d of October, making twenty-nine days.
| Washing, | 1 day. |
| Taking off the hair and swelling, | 3 do. |
| Tanning, | 25 do. |
| 29 days. |
Another ox hide, taken the 5th of September, was tanned the 3d of October, making twenty-eight days.
| Washing, | 1 day. |
| Taking off the hair and swelling, | 2 do. |
| Tanning, | 25 do. |
| 28 days. |
N.B. The tanning solutions made use of to these hides was less strong, and of a cooler temperature than usual, by which the time employed in the tanning operation was prolonged.
Calf Skins.
Sixteen very thick calf skins, taken the 18th of July, were tanned by the 31st of the same month.
| Washing, | 1 day. |
| Taking off the hair, | 8 do. |
| Tanning, | 4 do. |
| 13 days. |
Six calf skins, taken the 19th of July, were tanned the 2d of August, making fourteen days.
| Washing, | 2 days. |
| Taking off the hair, | 9 do. |
| Tanning, | 3 do. |
| 14 days. |
Six dried calf skins, began the 14th of August, were tanned the 28th of August.
| Washing, | 2 days. |
| Taking off the hair and swelling, | 11 do. |
| Tanning, | 1 do. |
| 14 days. |
Six calf skins, began the 20th of August, were finished the 10th of September.
| Taking off the hair and washing, | 20 days. |
| Tanning, (properly so called,) | 1 do. |
| 21 days. |
Three calf skins were brought from another tan-yard, the operation of tanning had been begun upon them, they having been thirteen days in the tanpit, in which it was intended they should have remained eleven months, (which was the usual time allowed such skins in the old way of tanning;) two of these skins were tanned in twenty-four hours, the third was tanned in forty-eight hours.
Six other calf skins took thirteen days.
| Washing and taking off the hair, | 6 days. |
| Tanning, | 7 do. |
| 13 days. |
Three salted Cow Hides,
Began the 14th of August, were finished the 12th of September.
| Washing and taking off the hair, | 20 days. |
| Tanning, | 9 do. |
| 29 days. |
One fresh Horse Hide,
Began the 30th of August, was finished the 13th of September.
| Washing, | 1 day. |
| Taking off the hair, | 6 do. |
| Tanning, | 7 do. |
| 14 days. |
Another fresh Horse Hide,
Began the 4th of September, was finished the 19th of September.
| Washing, | 1 day. |
| Taking off the hair, | 7 do. |
| Tanning, | 7 do. |
| 15 days. |
Two dried Sheep Skins,
Began the 14th of August, were finished the 12th of September.
| Washing and taking off the wool, | 25 days. |
| Tanning, | 4 do. |
| 29 days. |
Three Goat Skins,
Began the 16th of August, were finished the 10th of September.
| Washing and taking off the hair, | 23 days. |
| Tanning, | 2 do. |
| 25 days. |
Five Goat Skins,
Began the 19th of August, were finished the 10th of September.
| Washing and taking off the hair, | 20 days. |
| Tanning, | 2 do. |
| 22 days. |
The End
Footnotes
1 Save five per cent. on brewery sales—a war tax.
2 By some this construction of a steep may be thought too dear; in that case, a rough wooden one may be substituted, which, instead of placing outside the house, I would place on the upper floor of the malt house, so as to afford the opportunity of getting down its contents to the lower floor by means of a plug hole, which will save the labour of shovelling; but in summer, when this steep is not employed, it should be filled with lime water to prevent leaking, and to keep it sweet.
3 Twenty-seven parts of oxygen gas, and seventy-three of azotic gas.
4 Count Rumford on the Economy of Fuel.
5 Of the different kinds of hops, the long white is the most esteemed; it yields the greatest quantity, and is the most beautiful. The beauty of hops consists of their being of a pale bright green color. Care should be taken to obtain all of one sort; but if different sorts are used, they must be kept separate in the field, for there is a material difference in their time of ripening; and if mixed in the field, will occasion extra trouble at the time of gathering them in.
6 Hops must be dressed every year, as soon as the frost will permit; on this being well done depends, in a great measure, the success of the crop. It is thought by many to be the best method to manure the hop yard in the fall, and cover the hills entirely with the manure, asserting, with other advantages, that this prevents the frost from injuring plants during the winter. Hops had better be gathered before they are full ripe than remain till they are over ripe, for then they will lose their seed by the wind, or on being handled. The seed is the strongest part of the hop, and when they get too ripe will lose their green colour, which is very necessary to preserve as the most valuable part of the [remainder of text is illegible]
7 Kilns covered with the splinters of walnut, or ash, will answer the purpose, and come cheaper than hair cloth.
8 Stum is a certain quantity of white wine, strongly impregnated with sulphur. The mode of preparing it is as follows: A hogshead half filled with good white wine, or what is termed in French vin de grave; from fifteen to twenty long matches of sulphur are successively burned to this hogshead, with the bunghole closed. After this operation, the white wine becomes so impregnated with sulphur, that it has acquired all its taste and flavour, and is thus used as a ferment.