Another subject to which I gave some attention, while paying my respects to the tanners, was that of liming, and ob served that a wide difference .existed among them in relation to the time occupied in putting the hides through this process, and divesting them of the hair, which is of course the object of liming, primarily considered. Some of the best and most extensive manufacturers are so thoroughly satisfied of the in-j urious influence of lime upon the gelatin of the hide, that they have abandoned the use of lime altogether. That much of the gelatin can be extinguished by its too free application to the hide there now remains no doubt upon the minds of those who have fully tested it; others claim that by allowing the hides to remain in the lime from six to ten hours, they avoid any injurious influences. The superintendent for the firm of Craigan Co., Chicago, 111., informed me that he only allowed the hides to remain in the lime eight hours, during which time they are suspended on reels, kept by the application of steam up to 110 Fahrenheit, and the position of the hides frequently changed by turning the reels, after which they are taken off and placed in a pool containing pure water of a few degrees higher temperature, where they remain for twenty-four hours, during which time the water is changed two or three times, but constantly kept at the necessary tern-perat re, after which the hair is easily removed without in jury to the hands of the workman. The advantages claimed for this method are, that the hide does not by this rapid movement become so thoroughly im-preganted with lime, consequently less loss is sustained in gelatin. This is to be accounted for upon the principle, which perhaps is not generally known to those who have given but little attention to the influence of lime upon animal matter in a chemical relation, that by bringing the hide in direct communication with caustic lime and allowing it to remain too long, the texture and strength of the fiber are impaired to a greater or less extent, or in proportion as the lime is allowed to penetrate the hide, entering the pores and remaining in them in the form of caustic, carbonate, or lime soap, and cannot be entirely purged out by any amount of fulling, working, or baiting, without destroying a portion of the gelatin of the hide ;' and which was dislodged under the primitive method of working the stock through the beam house by low baiting, at the expense of a large portion of the gelatin, and was mainly the reason why the gain was so small in those days when thirty-five to forty per cent was considered all the best hide was capable of. Another evidence of t,he advantage of low liming,which is known to all practical tanners who have given the subject their attention, is, that all high limed leather is not only loose, and pervious to water, but will not produce the amount of gain that hides will that have been low limed, or divested of their hair, through the sweating process ; and under any process tanners should always bear in mind, that it is important that those who have charge of this department should not only be skilled thoroughly in their art but be con, stantly on duty, and observe closely the condition of the stock while passing through the Beam House ; and at the very earliest indication manifested by the hide, of yielding up the hair, it should be removed from the influence of the lime at once, and placed in a soak containing clean water, at a temperature a few degrees higher than the lime liquor they are taken out of, for the reason that it not only prevents the pores of the hide from contracting, but slightly expands them and aids the hide in its effort to give up the hair ; this will also avoid set-, ting the hair, which is often the case, when the hide alter being taken out of the lime, is thrown into cool water ; and by wrenching the hides in the pool through two or three baths of warm water the lime is purged out without the loss of gelatin which is incurred through the wrenching wheel ox fulling stocks, while the hide is in this loose and porous condition ; at which stage of its progress, great care should be observed that its substance is not wasted ; for therein consists; in a large degree the profit. While much has been said upon the subject of gain made by the manufacturer, I took considerable pains to inform myself upon this subject, also the average length of time occupied in tanning out a stock of sole or belting leather, and am satisfied, basing my calculations upon the most reliable data,, that the average gain made throughout the entire fraternity, is not over fifty per cent, and the time required to tan out the stock, six months. Some tanners make sixty and as high as sixty-eight per cent on some stocks, but these are the exceptions, and not the rule. And as further evidence of the influence of time upon the stock, I found, that in every instance where the greatest gains were made the hides had either been sweat or very low limed. It is supposed to be generally known that a new lime is more caustic than one that has been made for some time, whether it has been used or not; and will to a considerable extent bind the hair during the first few hours, rather than cause the hide to yield it up. This is caused by the influence of the caustic upon the cuticle of the hide, which, being very delicate, shrinks or contracts to a certain extent when brought directly in contact with the strong alkaline properties of the lime ; this can be modified to a great extent, bv allowing the lime to remain in the vessel in which it is slacked, for at least twenty-four hours. The water should be placed in the vessel first, and the lime thrown into it, and after the contents are thoroughly slacked it should be frequently plunged or stirred to allow the oxygen generated by the slacking process to escape, or become modified, and thereby changing the caustic properties into what is chemically known as lime soap, the influence of which upon the hides is, to soften it, without distending the fibers so severely, as will fresh slaked lime. Probably most practical tanners who have given the beam house much attention, have observed one fact, that when a pack of hides is taken from a new lime, they present a stiff, harsh appearance and feel, and the hair does not slip as freely, although longer going through the process, as when put through a lime liquor that has been used for several months, and which turns the hides out in a soft, pliable condition, and as a consequence yields up the hair much more readily. Some tanners only make entirely fresh or new limes, two or three times during the year, because their experience has instructed them, that a hide is more thoroughly and rapidly denuded of hair, through the medium of an old lime, than in a fresh one ; because the former is less caustic, and operates more directly upon upon the earthly matter deposited around the roots of the hair,and peihaps this is the reason why acids have been adopted by some, as a substitute for lime, as they are known to act more immediately upon the roots of the hair which are impregnated and surrounded with a material that partakes largely of carbon, which is to a greater or less extent imparted to the hair, and renders it almost invulnerable to decomposition. This element has a strong affinity for acetic acid, and is readily disolved by being brought in contact with it. Submitting these facts for consideration of the trade, we will pass on to give our view upon other matters no less important to the leather interest.
This article was originally published with the title "Practical Suggestions on Tanning Leather" in Scientific American 20, 17, 258-259 (April 1869)