BOOK V.
The science or art of Tanning is the process by which the animal hide or skin is converted intoleather, thus rendering it subservient to the use of man. The art of tanning in its most simple form was known to antiquity, and consisted simply in the drying and cleansing the skins, which were then converted into articles of clothing. Thus used, they answered but a temporary purpose, as the re-absorption of moisture would speedily cause them to decay. The Egyptians were among the earliest tanners of whom we have any definite account, and Thebes was justly celebrated for its artificers in leather. But unlike most of the arts in which the Egyptians excelled, they do not seem to have reached an equal degree of skill in the preparation of leather, although it was wrought by them into tapestry, and made to subserve various useful purposes. In later times this useful art has been reduced to scientific principles, owing to the investigations of Sir H. Davy, Sequin Proust,and others. Leather considered chemically is a compound of tannin and gelatine, possessing the qualities of durability, pliability, and insolubility in water.
The important elements in the manufacture of leather are, first,cleansing and softening the skins. Second, the depilation or removal of the hair. Lime is principally used for the latter purpose, although any agent which possesses the power to soften or destroy the roots of the hair, and facilitate its removal is equally desirable.
The process of depilation with lime is slow, and tanners have yet to learn that practically there are other chemical processes which will greatly facilitate it. Hydrosulphuret of calcium is recommended.
The great secret of tanning consists in so preparing the cuticle or porous surface of the hide as that the gluey or gelatinous tissue shall unite with the tannin. This is produced by immersing the skins in an infusion of oak bark, or other substances containing tannin. Therefore any process which will open the pores of the unhaired skins so that they become light and spongy and thus facilitate the union of the tannin with the tissue of the skin, is desirable. The name oftantakes its origin from a coarsely powdered bark, which contains the active principle in the tanning process. The component is calledtannin.
To Seguin, a celebrated French chemist, the discovery of a property in nut-galls of combining with the albumen and gelatine of skins, thus forming an insoluble and unalterable compound, is due. This is the key to the theory of tanning.
Morfit’s definition of the principle is, “to saturate a skin with tannin in such a manner as to promote the slow combination of this principle with the gelatine, albumen and fibrine contained in the former, so as to form with them a new compound. This reaction, in the operation of tanning, does not proceed spontaneously, but is the result of a slow process, requiring great care and skilful manipulation.”
Tannin exists in the bark of the trunks of nearly all perennial trees, and especially that portion of the bark next to the fibre and sap wood. It is found in the leaves of trees in small quantities. The oak-tree bark, leaves and fruit, contain a larger amount of tannin than any other tree species in North America. The bark is usually gathered from May to July, as during those and the intervening months they contain more tannin than during the other portions of the season. There are various kinds of oak in the United States, all of which yield a large amount of tannin. There is a species of oak which grows in Delaware, Maryland and Virginia, known by the name of Spanish Oak, which is superior for its tannin properties. The rock-chestnut oak, the black and white oaks, and Spanish oak, are considered the most valuable, and are used almost exclusively by the manufacturers of leather in the United States. The wood of almost every tree, the bark of which contains tannin, is also useful for the same purpose. There are several varieties of tannin. The pure tannin and the impure tannin is a generic term for the different varieties. It was a long time before tannin was separated in a pure state. It is so intimatelycombined with other extractive matter that it was with difficulty separated.
Chemists give us four varieties.
Natural tannin, comprising several species, originating from the different proportions of extractive and gallic acids. Also three kinds of artificial tannin, obtained by the action of nitric acid upon charcoal; also upon indigo and the various resins; also that obtained by the action of sulphuric acid upon the resins and camphor.
The best kinds of hides suitable for tanning into leather are those of heifers. The large ox hides are those which are used chiefly for conversion into sole leather. The skins of horses, cows, bulls, and buffaloes, are used for thick sole leather. For upper, thin, and the various fancy leathers, the skins of small animals, dogs, sheep, goats, seals, &c.
The quality of the leather depends upon several circumstances; the nature of the skin, its condition in curing, upon the method of tanning, also the nature of the food upon which the animal fed, and its healthiness. Hides from cattle slaughtered in cold weather are said to produce five per cent. more leather than when taken in the warm months. Dry hides produce more leather than salted hides. For the production of 40 pounds of leather, the average is estimated 30 pounds of dry hide—60 pounds of salted, or 74 pounds of market hide. Large supplies of skins are imported from Buenos Ayres, Brazil, California, and Texas. Sheep skins are received from the Cape of Good Hope and Buenos Ayres; goat skins from Barbary; lamb and kid from Italy.Very few hides, comparatively, are obtained at home. In order to form some idea of the extent of the leather trade, as represented in the tanning establishments, a few figures will enable the reader to judge.
There are, according to Morfit, 6,263 Tanneries in the United States, the largest number being in Pennsylvania. These unitedly employ 20,909 persons, and in which business is invested the sum of $18,900,557. The value of the products is $32,861,796. About 6,000,000 skins of sheep, goats and other small animals, are tanned and dressed annually, which are not included in the above estimate.
TheScientific American, in alluding to Morfit’s excellent work on the “Arts of Tanning,” had the following notice which we here insert:
“In looking over this book, and reading the different plans for improving leather, and for reducing the time occupied in tanning a skin or hide, we are more and more convinced of the important fact that the tanning art has been greatly improved by modern discoveries and application—a contrary opinion to that held by the universal mass of the people. We know it is very difficult to introduce new plans of tanning, for tanners are, like others, wedded to old things; thus the rolling of leather—an operation now generally practiced—was opposed with much bitterness by some of our most experienced tanners, one of whom said ‘he never would roll a hide while he lived,’ an assertion which he wisely lived either to forget or repudiate.
“The whole science of tanning depends on two principles, one the removal of the hair from the skin,with the least injury to the gelatinous matter of which it is composed, and the other is the rendering of the skin insoluble in water, and to resist the action of the atmosphere, and yet be flexible. The hair can be removed by lime, sweating, and other means, but the employment of a substance or substances that will combine with the gelatine of the skin to form a new substance, insoluble in water and incapable of being injuriously acted upon by the atmosphere, offers a wide field for the historian of the tanning art, and presents a subject for the study of every tanner at least in our country. The art of tanning was known, we suppose, before the flood; it is practised among all nations, civilized and savage, and the gist of it lies in soaking the skins in different solutions of various vegetable substances of an astringent character, until the tanning juices of those substances have combined with the whole skin and rendered it a new substance named leather. Oak and hemlock barks, sumac, willow, blackberries, catechu, kino, &c., are employed. Those who wish to get an account of the various processes and substances employed, must consult this book.
“We have only another remark to make, it is this, we have never known any of the metallic solutions to be employed in tanning, and from their nature, in rendering some vegetable substances insoluble, we believe that it would be worth the trouble for some of our tanners to make a few experiments. We would recommend the chloride of tin; it is made by feeding drop-tin into muriatic acid until effervescence ceases. The way to try it would be to make up asolution of it in a tub of cold water, until it stood about 1½° in the hydrometer; the skin should have undergone through the whole tanning process before it is placed in this solution, in which it should lie about two hours, and be stirred up two or three times. After this it should be well washed in cold water, and then finished in a milk-warm water bath, when it will be ready for drying. It is our opinion that a superior leather would be produced by this addition to any of the present processes.”
CHAPTER II.TANNING AND THE TANNING WOODS OF AMERICA.
The following letter in 1851 was addressed by Dr. Reid, of Rochester, New York, to Dr. Gale, of the United States Patent office, respecting the art of Tanning, and the various substances which are, or may be used in the processes. It is a very able and elaborate document, and will be found to contain not only facts, but important suggestions which must be valuable to all interested in tanning.
Dr. Gale—Dear Sir: As a chemist interested in the discovery of new chemical facts, and as an American citizen in the development of all branches of industry of our common country, permit me to call your attention to the following remarks and suggestions.
For two years and a half past I have been engaged, more or less of the time, in the investigation and development of an improved system of tanning, founded, as I flatter myself, upon a more correct knowledge of the chemical affinities and qualities of the various substances used, and of the processes employed in making leather.
The art of making leather embraces two species of operation, viz., the chemical and mechanical: the first includes all the changes produced in the raw hide, by means of other substances applied to it, till it becomes leather. The second, all the physical labor expended upon it, whether by manual tools or machinery. The first is by far the most essential and important, and yet it is that which is least understood by practical tanners. For the want of chemical knowledge they are, in a great degree, incapable of understanding and appreciating the chemical phenomena daily passing before their eyes; hence improvement in the art of leather-making has been very slow: and those improvements which have been attempted belong chiefly to the tools and machinery employed. Very few tanners have ever ventured upon an improvement in the chemical branch of their art; and when they have, their supposed inventions or discoveries were in direct contradiction of chemical laws, and of course were impracticable and soon abandoned: as, for instance, patents have been taken out for the use of potash and soda ash, dissolved in the tan liquor or ooze. One man, a few years since, actually obtained a patent for the suspension of bags of ashes in the tan vats. If he were a tanner he must have known, what every practical tanner knows, that lime, remaining in the hide, prevents the process of tanning, besides making bad leather; but he did not know that lime and potash were both alkalies, and that tannin was an acid, and that alkalies and acids neutralize each other, and therefore for his purpose, incompatible, or he never would have made such an absurd mistake.
For the last fifty years, nearly all the improvements, real or supposed, that have been patented, were chiefly for tools or machinery, for the purpose of expediting the mechanical labor necessarily employed, but the discovery and improvements which I have been investigating appertain solely to the chemical processes of tanning. They were first proposed by Harmon Hibbard, to whom letters patent were granted, as you are already aware; and with which improvements, and the chemical principles on which they are founded, you are familiar, having given them a careful and patient examination pending his application for a patent. But it is not my purpose to discuss these topics now, and I will dismiss this part of my subject by a quotation from Dr. Ure, and by offering a remark or two thereon.
In his dictionary of the Arts, Dr. Ure says:—“Various menstrua have been proposed for the purpose of expediting and improving the process of tanning; among others, lime-water and a solution of pearlash; but these two substances form compounds with tannin, which are not decomposable by gelatine; it follows that their effects must be prejudicial. There is very little reason to suppose that any bodies will be found, which, at the same time that they increase the solubility of tannin in water, will not likewise diminish its attraction for skin.”
Now the very objects here supposed by Dr. Ure to be unattainable, are literally and perfectly accomplished by Hibbard’s method, viz., a menstrum has been found “for expediting and improving the process of tanning,” and that, too, by “increasing atthe same time both the solubility of tannin and its attraction for gelatine or skin;” by means, also, so simple, direct and obvious, that it is wonderful that so learned a chemist as Dr. Ure should not himself have made the discovery.
But I come now to the principle object in view in this communication.
During the experiments and investigations above alluded to, my attention has been directed to two important branches of the manufacture of leather.
First. The chemical principles involved in the several processes of making the various kinds of leather, whether it be in “tawing,” as in making kid glove leather, or in oil dressing, as in making buckskin and chamois leather, or in tanning proper, as in making morocco, upper and sole leather.
Second. The various species and qualities of the tannin materials used, viz., the bark of hemlock, several varieties of oak, American and Sicily sumac, and terra japonica: these embrace the chief kinds used in this country.
It is to this latter—the materials for tanning—that I wish more particularly to call your attention.
We greatly need both a qualitative and quantitative analysis of the several kinds of substances used for tanning, especially of the hemlock bark—of the white, black, red, Spanish, chestnut, oak, and other varieties of the Quercus; also of the American and Sicily sumacs, and of catechu or terra japonica. We have many native trees and shrubs, of whose barks an analysis might prove to be something more than mere scientific curiosities.
A writer in one of our scientific journals asserts that the bark of the chestnut contains more tannin than oak, and more coloring matter than logwood of equal weights and qualities. On what authority he makes this statement, I know not, but if the fact be so, it should be established and known.
I am not ignorant that Sir Humphrey Davy and other distinguished foreign chemists have investigated this subject to considerable extent, but the barks and substances examined by them were not our indigenous products; besides, since their day, better and more accurate methods of analysis have been discovered, so that even their experiments need revision, and many of their conclusions may need correction.
According to Sir H. Davy, terra japonica contains about 54 per cent. of tannin, and is equal in tannin properties, to 6 or 7 lbs. of English oak bark, and to three lbs. of Sicily sumac. The tanners of this country consider American sumac as possessing only half the amount of tannin of the foreign and imported article; and it is worth only half as much per ton: hence it would require 6 lbs. of it to equal 1 lb. of terra japonica or catechu, and is, therefore, equal in tanning to English oak bark. But the hemlock of this country has probably double the amount of tannin that the white oak of the Northern States has; hence it holds a middle rank between Sicily sumac and terra japonica, and would consequently require 4 or 5 lbs. of it to equal one of the latter.
But the quality of the tannin, or rather the quality of the leather produced by these different kinds of tanning materials, is a matter of quite as muchimportance as the relative or absolute quantity of tanning contained in each of them. While terra japonica possesses the greatest quantity of tannin, it is considered as producing the most inferior quality of leather. So hemlock, which, excepting the Sicily sumac, possesses the next highest quantity, produce the next worst quality of leather; while the oaks, which are the lowest in the scale of quantity, afford the most superior in quality. And although the American and Sicily sumacs may be considered to be on a par with the oaks, as to quality, yet the same law seems to hold with respect to each other; that is, the American sumac, which possesses only about half the amount of tannin, makes a better quality of leather than the Sicily sumac.
Nowpuretannin is probably the same in all cases, then why this great diversity of quality in the leather? A careful chemical analysis of the substances used, would determine the question; but, in the absence of such analysis, we readily and perhaps correctly conjecture, that very different vegetable gums, resins, acids, extracts, &c., must be combined with the tannin in these several tanning materials, which being also soluble in water, combine in some way with the gelatine of the hide as well as the tannin, and become fixed, although none of them could alone be made to unite thus permanently with the hide. It becomes, therefore, a matter of much importance to the tanner to know what these several vegetable products are which are combined with the tannin of each species of bark, or substance used for tanning, and as they are not merely useless, but injurious, to know how,if possible, he may get rid of them. Among these products, there is in hemlock bark a large amount of resin or pitch, a small portion of which, however, is soluble, unless very hot water is used in leeching the bark; but in all barks there is, besides extractive or coloring matter, a large amount of acetite of potash, which is nearly as soluble as tannin itself, and which is always leeched out of the bark and forms a part of the tan liquor or ooze in which the tanner steeps his hides. That the potash, which abounds in all barks, is leeched out, is evident from the fact, that ashes, obtained from burning the leeched bark of tan yards, will not afford a ley sufficiently strong to make soap. The same thing is true of wood that has been long soaked in water. The black oak or Quercitron—the Quercus Tinetosia which is so valuable for its coloring properties, is among the richest of barks in tannin, and makes the best quality of leather, but it is generally abhorred by tanners, and avoided in the first stages of tanning. It abounds in a rich, deep yellow precipitate, which attaches itself, like paint, so tenaciously to the surface of the hides, that the tannin penetrates very slowly. But by the Hibbard process of tanning, the hydrochloric acid used decomposes and neutralizes both the potash and coloring matters leeched out of the bark, in a great degree, so that the process of tanning is more rapid, and the color of the leather much fairer and more beautiful, besides it, the leather, being tougher and more pliable.
Here then, in the analysis of our indigenous barks, is a field large enough to give useful and honorableemployment to all the first chemists of the country. Not possessing, myself, either the time, skill, or requisite means to pursue this subject, but believing that you possessed them all, in addition to a taste and zeal for such pursuits, I have taken the liberty to present those views and suggestions for your consideration.
There are other matters connected with this subject which belong rather to the commercial and agricultural business of the country, but are not wholly devoid of interest to the naturalist and chemist. I allude to the quality and quantity of tanning materials as produced and influenced by latitude, locality, and climate. In the Eastern, Northern, and Western States the quality and quantity of tan barks are far inferior to those of the Middle, Southern, and South-western. The facilities and natural resources of the South for manufacturing leather, over those of the North, as far exceeds those of the latter, as the actual amount of leather and shoes manufactured by the North exceeds those manufactured by the South.
The South, in fact, ought to furnish the North with leather; and should, moreover, produce all the sumac needed for home consumption, both for dyeing and tanning, of which we now import large quantities. By procuring from the coast of the Mediterranean the best varieties of sumac, viz., the Rhus Coriana and the Rus Cotinus—the former used chiefly in tanning, and the latter in dyeing, the South might grow enough in a few years for export, and find it a profitable branch of industry.
CHAPTER III.PRACTICAL HINTS ON TANNING.
The Hon. Zadock Pratt, one of the largest Tanners in the State of New York, has given some very valuable information concerning the various tanning processes which his experience and knowledge have afforded him. We shall select a few of the most important as furnished by him to Morfit’s valuable work.
Skins with the hair on are first soaked in cold water for forty-eight hours, and are then subjected to the action of the machine (Monier & Ray’s Mill) for an hour and a half; exposure for which time is generally sufficient to render them pliable. Eight or ten skins, according to their size and thickness, are generally contained in the apparatus. The water is then allowed to drain off, a sufficient quantity of cream of lime is poured in and the skins are again beaten for four hours, when they are taken out and piled up. After having been left to drain for five hours in this position, they are again fulled for a time in the machine, and then are deprived of their hair and fleshed by the workmen. They are thenbeaten for an hour and a half in the machine, and cleaned and scraped with the slate. In order to remove the lime, some of which remains attached to the skins, they are now soaked in water containing one hundredth part of sulphuric acid, and, after being constantly stirred in this liquid for an hour, are washed and rinsed in running water.
This method of preparing skins for tanning dispenses with the laborious manipulations to which they are commonly subjected, and preserves their quality, not injured as they are in the old way, by the hands of the workmen. It also presents the additional advantage, that they do not require the long exposure to the action of lime which is so apt to injure their tissue.
Since I first commenced business, the gain of weight in converting hides into leather, has been increased nearly 50 per cent. That is, from a quarter to a third more leather can now be obtained from a given quantity of hides, than at the time when I learned my trade at my father’s tannery, conducted in the old fashioned way, some forty years ago. The great improvement in weight seems to have been gained by the judicious use of strong liquors, or “ooze,” obtained from finely ground bark, and by skilful tanning.
The loss and wastage upon hides, from hair, flesh, &c., may be estimated at from 12 to 15 per cent.
To green hides, particularly, nothing can be more injurious than to suffer them to remain too long in weak ooze. On the other hand, however, the effects of an early application of ooze, that is too strong andtoo warm, to green hides, is very injurious. It contracts the surface fibres of the skin, tanning at once the external layers so “dead,” as it is termed, as to shut up the pores, and prevent the tannin from penetrating the interior. In the impossibility of adapting fixed rules to the innumerable variety of cases, nothing can be depended upon but the judgment of the practical tanner. In softening hides, and preparing them for the process of tanning, a great deal depends upon the judgment of the one superintending the operation.
In “sweating,” the character of the hides, and the temperature, are essential, but ever-varying considerations. As a general rule, however, the milder the process for preparing the hides for the bark, the better. Too high a temperature is particularly to be avoided. Hides that are very stiff and hard, resisting all the ordinary modes of softening, are assisted by a solution of ashes, potash, or even common salt will be found beneficial; and particularly so in hot weather.
The following table may be found useful in conveying an approximation to a definite idea of the practice in my tannery:
I would here remark that I changed the process from liming to sweating in the sole leather in 1836—theonly change I have made in tanning for twenty years; and for sole leather, it has been proved to be quite as good as liming, if not better, and somewhat cheaper; besides yielding a greater gain of weight, and when well tanned, making leather more impervious to water. Liming and “bating,” however, for light leather, is preferable. Salted hides do not require more than two-thirds the time to soak; but generally rather longer to sweat. After the hides are prepared for tanning, the next process is what is commonly called “handling,” which should be performed two or three times a day in a weak “ooze” until the grain is colored. New liquors, or a mixture of new and old, are preferable for Spanish or dry hides—old liquors for slaughter. They are then, after a fortnight, laid away in bark, and changed once in two or four weeks, until tanned. Much care and judgment are necessary in proportioning the continually increasing strength of the liquors to the requirements of the leather in the different stages of this process. The liquors should be kept as cool as possible, within certain limits, but ought never to exceed a temperature of eighty degrees; in fact, a much lower temperature is the maximum point, if the liquor is very strong; too high a heat, with a liquor too strongly charged with the tanning principle, being invariably injurious to the life and color of the leather. From this it would seem that time is an essential element in the process of tanning, and that we cannot make up for the want of it by increasing the strength of the liquor, or raising the temperature at which the process is conducted, anymore than we can fatten an ox or horse by giving him more than he can eat.
Hides that are treated with liquor below the proper strength become much relaxed in their texture, and lose a portion of their gelatine. The leather necessarily loses in weight and compactness, and is much more porous and pervious to water. The warmer these weak solutions are applied, the greater this loss of gelatine. To ascertain whether a portion of weak liquor contains any gelatine in solution, it is only necessary to strain a little of it in a glass, and then add a small quantity of a stronger liquor. The excess of tannin in the strong, seizing upon the dissolved gelatine in the weak liquor, will combine with it, and be precipitated in flakes, of a dark, curdled appearance, to the bottom. At the Prattsville Tannery, the greatest strength of liquor used for “handling,” as indicated by Pike’sbark-ometer, (an instrument to test onlyFRESHLYmade liquors,) is sixteen degrees; of that employed in laying away, the greatest strength varies from thirty-five to forty-five degrees.
After the leather has been thoroughly tanned and rinsed, or scrubbed by a brush-machine or broom, it will tend very much to improve its color and pliability to stack it up in piles, and allow it to sweat until it becomes a little slippery from a kind of mucus that collects upon its surface. A little oil added at this stage of the process, or just before rolling, is found to be very useful.
Great caution is necessary in the admission of air, in drying when first hung up to dry. No more airthan is sufficient to keep the sides from moulding, should be allowed. Too much air, or in other words, if dried too rapidly, in a current of air, will injure the color, giving a darker hue and rendering the leather harsh and brittle. * * * *
The average time of tanning in 1842, was five months and seventeen days; of 1843, five months and twenty-two days; 1844, six months; 1845, six months and eleven days; average of the whole time, five months and twenty-seven days. The average weight of the leather was over eighteen and one-half pounds per side. This, according to the best authorities we have, is considerably below the time employed in England. There, it is no uncommon thing for eight or ten months to be employed in tanning a stock of leather, and some of the heaviest leather, it is said, takes fourteen and eighteen months. Such deliberation undoubtedly insures a fine quality of leather, but it may be questioned whether there is not a great loss of weight—a loss of interest on capital, and in consequence an unnecessary enhancement of price, which does not suit the American market.
The tanning of leather, more than almost any other manufacture, is a chemical process, the success of which depends almost wholly upon the skill and judgment with which its complicated manipulations are conducted. To attain the requisite skill in the laboratory of the chemist, is evidently impossible; it can only be acquired in tanning itself, by long and careful attention and observation.
The labor in the loft and peeling bark during theabove five years was 8820 days. One man will work through the beam-house, in one year, 6260 sides. One man will tan and finish 2228 sides. One cord of bark tans 196 pounds.
The question has been frequently asked me, how long does it take to tan sole leather. I answer, from four to six months, according to the strength of the liquor and the number of sides in the vats; and the quicker tanned the better.
If the hides are fresh, they are capable of being properly softened, and, if so, the process of tanning may be completed much sooner than in the case of old and hard hides, that cannot be softened with the same facility.
If the hides have sufficient room in the vats, so as not to lay crowded, they will tan much faster.
As the tanning advances, the liquor should be renewed seasonably, and its strength increased in a ratio proportionate to each stage of tanning.
The question, “Is the leather to be tanned so as to barely pass in market, or to be well prepared, so as to make firm and solid leather?” involves a consideration of much importance.
Every one interested in the science of tanning should purchase and study the able and elaborate work upon the subject by Morfit. No portion of this important art is left untouched, and the work gives abundant evidence of laborious research, and intelligent compilation, combined with a thorough knowledge of the subject.
CHAPTER IV.HIBBARD’S PROCESS OF TANNING.
We herewith give the specification of this important patent, allusion to which is made in the letter of Dr. Reid:
To all whom it may concern:—Be it known that I, William W. Reid, of the city of Rochester, in the county of Monroe, and State of New York, assignee of Letters Patent of the United States, granted to Herman Hibbard, of the town of Henrietta, in the county and State aforesaid, for certain improvements in “Tanning by Tannin and acids,” which Letters Patent, bearing date the 16th day of October, 1849, were assigned to me on the 23d day of October, of the same year, by deed, which deed was duly recorded on the 24th of Nov., year aforesaid, believing that said Letters Patent are inoperative, and invalid by reason of a defective specification, have surrendered the same, and according to the requirements of the Acts of Congress in such case made and provided, have applied for a re-issue of Letters Patent, for the same improvements under the specification of the words following, viz.: The invention and discoveryof Herman Hibbard, consist in new and useful improvements in the preparing of hides and skins for tanning, and in the art or mode of tanning the same, with or without the hair or wool upon them, thereby making leather suitable for the various purposes to which hides and skins thus tanned may be applied.
First, the nature of his invention, so far as relates to the preparation of hides and skins for tanning, consists in the use of a composition of lime, wood-ashes or potash and salt, for the purpose of removing hair or wool, and also for the process of “Liming,” so called, instead of using lime alone as in the old method.
Lime and ashes or potash, and even salt in weak solution, have been used separately for the purpose of removing hair and wool, and also for the process of “Liming,” that is for removing grease, mucus, and other impurities from hides and skins, but not as above combined.
It requires several days and sometimes weeks to effect these several objects, by the use of lime alone. Moreover, lime being nearly insoluble, the hides become impregnated therewith, so that bates and drenches and much labor are required to remove it, before the hides are in a suitable condition to receive the tannin, in consequence of which, their muscular fibre and texture are materially injured. But potash being very soluble, is easily washed or worked out by water alone; besides, it has a greater affinity for fat or oil, and makes a soluble soap, which is also easily worked out; but lime makes an insoluble soap, which is removed with more difficulty; potash beingsoluble, penetrates and softens the hide more speedily, and thus enables the lime itself to act sooner than it could alone. But fresh quick lime loosens hair sooner than potash. Thus the two conjoined, subserve a better purpose than either singly.
Salt, in solution, also aids in softening dry or hard hides. It protects the substance of the hide from the too caustic action of the alkalies—loosens dirt, grease, &c., and thereby purifies the skin. It might be omitted in treating salted hides unless soaked too long in water. But in all cases it preserves the substance and weight of the hides, while undergoing the liming process.
Second, the nature of Hibbard’s invention, so far as it relates to the process of tanning, consists in the use of a composition of salt, sulphuric acid, and sumac, oak, hemlock bark, or any other tannin used for tanning.
The salt, sulphuric acid, and tannin being mixed together in water, in certain proportions hereafter mentioned, a portion of the salt is decomposed by the sulphuric acid, forming sulphate of soda and setting the muriatic acid free, which (the muriatic acid) being absorbed by the water acts directly and rapidly on whatever of the alkalies may yet remain in the skins, dissolving and removing them, while it acts with equal rapidity on the hide itself, “raising it,” or opening its pores, prepares it to receive the tannin, which, being present also in the mixture, immediately unites with the gelatine of the hide, forming leather more expeditiously than by the old method.
To enable others skilled in the art of tanning to use this method, let them observe the following:
For unhairing and liming, so called, and for pulling wool, prepare and use the following composition, which we denominate—
Composition No. 1.—Good wood ashes, 1 bushel (or potash about 5 pounds); fresh slaked lime 4 quarts; salt about 3 quarts; water about 100 gallons.
These ingredients may be mixed together and the hides be put into the mixture, for unhairing and liming. But for pulling wool, take lime and ashes equal parts, and salt 1 quart, to one bushel of the mixture and mix with water sufficient to make a thin paste, which is to be applied to the flesh sides of the skins in the usual way, and kept at a temperature of 60° to 68° F.
Or a better method may be to leach the ashes, or, when potash is used, to dissolve it in the water. To the clear ley add the lime and salt, and use the mixture for unhairing and liming. But for pulling wool mix 1 bushel of lime and 1 quart of salt with good strong ley, making a thin paste, which apply to the flesh sides of the skins, as already described.
A little practice will enable the operator to judge of the proper strength of composition No. 1. It should have a slippery feel and quite a sharp alkaline taste. It is readily made stronger by the addition of more materials, or weaker by adding water.
The above quantities and proportions serve as a general guide. The lime and ashes or potash may be used in various proportions, but it is desirable thatas little lime as possible to produce the desired effect, should be used, because of its insolubility and of its insinuating itself into the substance of the hide. The hides or skins having been properly soaked, softened, and broken, are to be put into composition No. 1, in a vat or vats, and handled in the usual way. The temperature may be kept at 50° to 60° F.
As soon as the hair will come freely, they must be taken out and put into clean soft warm water, and soaked several hours, then thoroughly worked, flesh and grain, on the beam. Then put back into the water, soaked again and worked again, till they are sufficiently reduced. They are then ready for the tanning process. As a general thing, bates and drenches will not be required, because the potash being soluble, and the little lime used, are easily washed out with water, and because composition No. 2, about to be described, used in the tanning, accomplishes the identical objects to be obtained by bating and drenching. If any prefer, they may prepare their hides and skins after the old method. They can be tanned just as well by composition No. 2, but skins and hides prepared by the foregoing method will make heavier and stronger leather, than when prepared by the old process of tanning and bating.
For tanning, make and use the following which we denominate—
Composition No. 2.—Take sumac, oak bark, quercitron, or any other tanning material, either singly, or combined; leach and make a strong infusion or ooze. To every 100 gals. of ooze add salt, 20 lbs.; sulphuric acid 2 pints.
These quantities serve as a general rule. A little experience will enable a workman to determine by the color and taste, as to the requisite proportions and quantities and strength of the composition without weighing or measuring.
The salt should always be in excess over the acid. If it is considerably more so, no harm can accrue, but if the acid should be in excess, injury might be done. There should be sulphuric acid enough to decompose enough of the salt to liberate an equivalent of muriatic acid, of which there should be as much as is sufficient to give the hides a uniform color, and cause them to swell or puff up slightly.
The muriatic acid thus generated by the decomposition of the salt, by means of the sulphuric acid, attacks the alkalies that may remain in the hides, dissolves or converts them into soluble muriates of lime or potash, and thus acts as a bate and drench on the hides, to clean them, while at the same time it opens their pores, so that they imbibe the tannin more rapidly. It also precipitates or decomposes a portion of the coloring matter of the ooze, and thereby renders the color of the leather lighter, more lively and beautiful.
If there is a deficiency of acid, so as not to neutralize all the alkalies remaining in the hides, they will be spotted or dark colored. They will not raise or swell up. In such case, more of the sulphuric acid must be added for the purpose of decomposing more of the salt (which is supposed to be in excess) and thus furnish more of the muriatic acid.
N. B.—Muriatic acid of commerce may be addedto the tannin and salt, and they will produce nearly the same result; the sulphate of soda would be wanting, but this also may be added, and then we should have the same composition, and precisely the same results; and when economy would warrant it, this course might be adopted, but at the present cost of these materials, it is cheaper to use sulphuric acid and salt, and thus generate both the muriatic acid and sulphate of soda; this method is also more simple.
The hides and skins having been prepared in Composition No. 1, as already described, they are then to be put into Composition No. 2, prepared as above, in suitable vats, and handled often in the usual way. The strength of the composition must be kept up by additions of strong ooze, and also of salt and acid when necessary, and in such quantities as will give the original taste, color, &c.
The time required to accomplish the process of tanning will depend on the quality and size of the hides or skins, or kinds of leather to be made, and on the strength and temperature of the composition. It the strength be good, the temperature about 80°, and the handling properly conducted, most kinds of leather may be tanned in less than half the time required by the old method of tanning now in use in our country. When the hides are sufficiently tanned, those designed to be curried may be curried and finished in the usual way. If the process has been properly conducted, they will require much less scouring, whereby some hard labor is saved.
When it is intended to black and finish on the grain, in order to remove any excess of salt and acid that may remain in them and interfere with the finishing, after removing them from the vats, soak them an hour or less in a clear ooze, made of the same kind of tannin used in tanning them; then rinse and strike them out of clear soft water, after which immerse them in the following composition:—To every gallon of soft water add, of good soft soap 1 quart; best sperm or cod oil, 1 pint. Mix and beat these ingredients well together; after being dipped in this mixture let them “sammy” or dry partially, then sham set and stuff them. For stuffing, use common stuffing and soft soap, equal parts, or sad and cod oil, equal parts; after which, if to be finished on the flesh side, proceed in the usual way, but if it be blacked on the grain, wet or sponge them, when nearly dry, on the grain side with a weak solution of potash or sal soda, then apply a thin coat of blood and acetate of iron, as used by morocco dressers; let them nearly dry, then repeat the coat of sal soda and mixture of blood and acetate of iron. Then set them smooth on both sides, and oil and dry them.
Deer, sheep, and similar skins, designed for buck, or imitation of buck, such as are used for gloves, mittens, and military trimmings, should be “frized” after being prepared in Composition No. 1, and unhaired; and then tanned in Composition No. 2, prepared with sumac. When tanned, rinse and strike them out of clean soft water, then hang up to dry. When dry, finish on a perch with a stake, moon-knife, and pumice stone; or, to make them soft andelastic, they may be milled first, before quite dry, and then finished with perch, moon-knife, &c., the same as in oil dressing, but without any oil.
In order to tan hides or skins with fur, hair, or wool on, they must first be washed thoroughly clean in a weak potash ley, or in soft soap and water (care being taken not to keep them in so long as to start or loosen the fur, &c.,) then flesh and break them; rinse in clean soft water, then tan them in composition No. 2. To make white leather, sumac should be used in making composition No. 2. What I claim and desire to secure by Letters Patent, is, first, the process of removing the hair and wool from hides and skins, and of liming them, so called, preparatory to tanning by the use of a composition of lime, wood ashes or potash, and of salt, called Composition No. 1, in the manner above described.
I also claim the use of a composition of lime and wood ashes or potash, without the salt, but I do not claim either of these materials separately by itself.
Second, I claim the process of tanning hides and skins by the use of any kind of tannin, in combination either with the muriatic acid of commerce, or with muriatic acid generated by a mixture of sulphuric acid and salt in water, with the tannin, in the manner substantially as above described.