# Popular Science Monthly/Volume 41/July 1892/The Development of American Industries Since Columbus: Leather Industry I

Next in series
Layout 4
* LEATHER-MAKING.
By GEORGE A. RICH.
XV. DEVELOPMENT OF AMERICAN INDUSTRIES SINCE COLUMBUS.
ZADOCK PRATT, the great leather manufacturer, once gave as his toast at a notable trade dinner, "There is nothing like leather." The determined, enterprising spirit indicated by that sentiment may be said to be the distinguishing mark of the modern tanner, and it is possible that therein lies the explanation why one in tracing the course of that industry must look so largely to recent years for progress and development. But the course of this development furnishes an interesting commentary upon the application, or more accurately, perhaps, the lack of application, of the principles of science to this one of the industrial arts. Now, the art of tanning is one in which a knowledge of science, especially of chemical science, could be made to do most effective service. The operation is essentially a chemical one. Yet, as a matter of fact, since the first demonstration of the union of gelatin and tannin, chemistry has done almost nothing to facilitate the operation. It is not to that that the industry owes its remarkable progress; rather, it is to the invention of improved apparatus for hastening old processes. Just estimate, of course, must be made of the fact that the scientific knowledge of the principles involved in tanning did much to make these inventions possible. At the same time, however, as Mr. C. T. Davis has remarked in his admirable treatise upon leather: "Take ​away our bark and hide mills, improved leaches and vats, handling and stuffing appliances, and other improved constructions; our splitting, scouring, boarding, whitening, polishing, pebbling, and other modern mechanical inventions, and our steam-power so economically derived from the use of spent tan as fuel; turn us out of doors to work among the rude contrivances of a century past, and would the result of our labor show an extraordinary gain either in time or quality over that of our predecessors?" Any review of this development, therefore, though it is a record of splendid achievements, is not one of the discovery or introduction
Fig. 1.—Section of Animal Skin (magnified), a, epidermis; b, dermis; c, corium, or base of the skin; d, fibrous tissue; e, fat-cells; f and g, ducts of the sweat-gland; h, sweat-glands; i, hair; k, hair-bulb; l, sebaceous gland.
of new principles. It is a record of mechanical improvements and business economy.
Unfortunately, history gives us little definite information regarding the origin of this one of the industrial arts. Surmises, however, go for considerable in this case. The skins of birds and animals formed a large part of the first clothing of man. Now these would be found to grow hard and horny in their natural state, and on exposure to moisture to become putrid and offensive. Efforts to counteract this, and at the same time to render the skins soft and pliable for use, would be most natural, and to these are traced the beginning of the leather industry—an industry which ​in its inception can properly bear no wider designation than the "dressing of skins."
Leather, in the broad application of the term, is a combination of gelatin and mineral salts, oil or tannic acid. The hide or skin Fig. 2.—Divisions of a Hide. A B C D is termed the "butt," and the halves of the butt marked by the dividing line E F are known as "bends." H H are the "cheeks," while the upper portion of the butt figures as the "shoulders." of an animal consists of two layers—the outer (epidermis), a hard cellular plate into which neither nerves nor blood-vessels penetrate; and the inner, or true skin (dermis), a dense membrane composed of fibers interlacing in a curiously complex manner. These connecting fibers consist almost wholly of gelatigenous tissues. They will dissolve in boiling water, thus forming gelatin, will enter into solution with concentrated acids and alkalies, and will combine with oil and tannin. As such this tissue forms the basis of all leather, and the labor of the tanner becomes one of bringing it into chemical or mechanical combination with these other components.
The original process of curing skins was probably the simple one of cleaning and drying them. Removal of the hair by maceration in water seems to have been common among the very early tribes, and one writer has suggested that the idea was obtained from the natural process of depilation. They must certainly have been familiar with it in the case of drowned animals, where maceration can be plainly observed. Following this, smoke, sour milk, oil, and the brains of the animals themselves were found efficacious. Many of these primitive methods are employed at the present time, thus bringing into novel conjunction the days of the roving Massagetæ and those of the thrifty American. An acquaintance of the writer, a Massachusetts tanner, traveling recently through the province of Winnipeg, chanced upon a small Indian village. The place was in no way interesting except in the employment of the squaws. They were all busily engaged in removing the hair and muscles from the skins, largely those of deer and moose, which the bucks had taken in the chase. This they did by means of sharpened bones which they plied in a vigorous manner, rubbing away both flesh and hair. The skins, it seemed, had been taken from the animals some time before, and together with the brains partially dried in the sun. After the squaws had completed this scraping process, the skins were steeped in a lather-like mixture made from water and dried brains, and were then reduced to a soft texture by frequent ​kneading and similar manipulation. Ten days later this same manufacturer was in Peabody, Mass., in one of the most complete of modern tanneries, and, though the space of time intervening was only a little more than a week, yet in it he had traversed the whole gamut of the art.
Fig. 4.—Old Putnam Tannery in Salem Mass.
​hand a considerable foundation upon which to begin the development of their art. But, once known, its extension could not be hindered. Herodotus states that the Libyans wore leather clothing, and that the Phœnicians, whose home was a barren stretch of shore, depended largely upon it in the construction of their
Fig. 5.—Dash-wheel.
ships. Persian and Babylonian leather was long celebrated, and as early as the beginning of the Christian era the Russians were famous as skilled tanners. Hungary, too, acquired an early name for its leather, having learned a peculiar process for making it from Senegal. Boucher carried the art into France; while Colbert, the enthusiastic patron of all the industries, did all that he could in the way of personal and public effort to extend it. Thus it was that leather became more and more an article of general use, and thus it was that by the time Columbus started on his hazardous voyages there had already grown up a considerable industry in England, France, Spain, Germany, and Russia.
But despite all this growth the processes involved in the operation of tanning were not really understood until the close of the eighteenth century, when they became objects of scientific study. Before that time the art was purely an empirical one. The immediate successors of Columbus brought with them to America such crude knowledge of it as was current at the time. Leather being a prime necessity, tanneries were started soon after the settlement of each community, either by the men of that craft or by the large farmers for their own convenience. Leather formed at that time no small part of people's clothing; indeed, leather breeches appeared clear into the eighteenth century, though the wearing of them was largely confined to servants and laborers. ​It figured in nearly all the arts. It was used for harnesses and saddles. It was fashioned into boxes and articles of ornament. It served both as a protection and defense. Nevertheless, but little progress could be made until the settlers had obtained a stock of domestic cattle. Columbus is said to have brought the first of these animals to America on his second voyage thither in 1493. By 1610 they had been introduced into Virginia, while Plymouth and the New Netherlands received a supply a few years later. Tanneries then were started North and South. In a list of tradesmen to be sent to Virginia in 1620 are enumerated tanners, leather workers, and shoe-workers. In 1649 Captain Matthews, an active
figure in Virginian history, received legislative commendation for his enterprise in the building of a tan-house, the manufacture of leather, and the employment of eight shoe-workers. The Virginia Assembly, however, a dozen years afterward had to come to the rescue of the industry, passing a law which required that ​tan-houses should be built in every county at the county charge, and that provision should be made for the employment of tanners and curriers. The rates of hides and shoes were fixed, and stringent efforts were made to prevent the exportation of hides. Maryland adopted similar measures; but Beverly, writing a few years later, says of these enterprises that "a few hides were with much ado tanned and made into servants' shoes, but at so careless a rate that planters don't care to try them if they can get others."
Fortunately, the industry fared better in its first planting in New England, and Higginson probably struck the secret of this good fortune when, in 1630, he called attention to the extraordinary increase of cattle in Massachusetts, and the "store of sumacke trees, good for dyeing and tanning leather." Cattle continued to multiply rapidly from 1630 to 1650, but the prices placed upon them were so high that few were slaughtered. But in the latter year the cessation of immigration from Europe caused a depression in the cattle market, and they began to be killed freely, thus supplying the tanners with the necessary hides. The Massachusetts General Court, in 1640, recognized the importance of the industry, and passed a law punishing those who slaughtered cattle and neglected to save the hides and have them tanned. But Connecticut, Massachusetts, and Rhode Island thought that they must take a stronger hand in the pushing of this industry those were in truth the days of infant industries, and of detailed trade regulations and so special laws were passed for that purpose. Protection, in the current political sense of the word, was not known then, but the same ends were attained through the guild privileges. The general law of Massachusetts, passed in 1642, is typical of these regulations. This declared that no leather overlimed or insufficiently tanned, or not thoroughly dried after tanning, should be exposed for sale. Tanners putting leather into hot or warm "moors," where the leather should heat and burn, were to forfeit twenty pounds for each offense. Curriers were not to dress any leather imperfectly tanned or dried, nor use "any deceitful or subtle mixture, thing, way or means to corrupt or hurt the leather, nor curry any sole leather with anything but with good, hard tallow, nor with less than the leather would receive; nor dress or curry any upper leather but with good and sufficient stuff, not salt, and should thoroughly liquor it until it would receive no more; they were not to burn or scald any leather in the currying, on forfeiture for every one marred by unworkmanlike handling, to be judged by the oath of sufficient witnesses."
Fig. 7.—Corner in a Beam House.
​stated that these laws were passed in consideration "of the damage or injury which many sustained by the ill-curing of leather, and by the shoemakers in making it up into shoes and boots." Thus left to shift for itself, the industry steadily though slowly progressed with the country until 1860, when new inventions and improvements in processes, and energetic men at the head of it, gave it a decided impetus which has constantly gained in force since.
As has been said, the fundamental processes of tanning have changed very little since the early days. The hides, as they came
Fig. 8.—Union Splitting Machine.
to the tanner, were first washed, and then, in order to remove the hair, soaked in vats of water and lime or ashes. After having been thus unhaired, they were put over a beam and scraped until every remnant of flesh had been removed. After another washing they were "laid away"—that is, packed in vats in alternate layers of ground hemlock or oak bark. The object of this was to bring about the desired union of the gelatin and tannin. The operation, however, was a slow one, and oftentimes many months were required to complete it. But study, of course, has been since given to the details of these various steps, which has resulted in a marked saving of time. In the preliminary process of depilation there are two methods which are now commonly followed by American tanners. The first is known as the "liming," which is used largely in the preparation of upper leather; and the second, known as "sweating," which is used for sole leather. In the "liming" process the hides are soaked in a solution of lime and water, as indicated above, until the hair-bulbs are loosened. In sweating there are two methods also: the warm sweat, with the temperature of the pit at 100°; and the cold sweat, with it at 50° or 60°. The former method is in general use in southern Europe, while the latter is not only American in origin, but is the ​favorite one with tanners on this side of the water. Again, the process of depilation is still further hastened by the use of a mineral acid, like sulphuric, or by the handling of the hides in the old sour liquors where the tannic acid has become largely converted into gallic acid. There are strong advocates of both cold sweating and warm sweating, and of acid and non-acid methods, but there are no data on which pre-eminence can be assigned to any one of them. All have played an important part in abbreviating the tanner's work. Following depilation the hides are colored or passed through a series of vats containing liquors of varying strengths, and then laid away. Here, also, it is a matter of opinion as to what is the proper time that should be given to each of these operations. The late Hon. Gideon Lee, in a course of lectures on the art of tanning, declared, that he found quick-tanned leather of firmer and closer texture, and at the same time heavier and more durable. By keeping the hides too long in the liquors or vats the gelatin was disolved. But, whatever the general census of opinion, these processes have reduced the time required in the tanning of a hide from twelve and eighteen months to four and six months. Visions of a still greater abbreviation have been common, and "quick tanning processes" appear about so often. Some of these are historical. They include attempts to force the tannin into the hide by
Fig. 9.—Belt Splitting Machine.
hydrostatic pressure, and by the pressure of the air under an exhausted receiver. They include the application of the principles of osmose and kyanizing. The latter experiment was made by a young English engineer, who in his early life had been engaged in preserving wood by kyanizing with chemical agents. He came to this country and spent ten thousand dollars in constructing a large iron, egg-shaped, copper-lined tank. This was capable of holding one hundred butts, and of resisting an immense pressure. He provided pumps so that he could exhaust the air of this tank, ​converting it into an almost perfect vacuum, and at the same time force liquor into it, producing a pressure of one hundred pounds to the square inch. Between the hides he placed cocoa matting, so that the free circulation of the liquor should be in no way interfered with. In the top of the tank, where it was impossible to put hides, some small blocks of wood were placed. He afterward exhausted the air in his tank, forced in the liquor, and then waited several days, but his experiment was a complete failure. On examining the contents of the tank, he found the wood thoroughly saturated with tannin, but the hides were scarcely colored. The pressure that would kyanize wood would not tan leather. Recently attempts have been made to employ
Fig. 10.—Scouring Machine.
electricity to hasten the operation, but as yet no practical and satisfactory "quick tanning" process has been found.
Few, if any, of the pioneer tanneries remain. That, however, which used to belong to Mathias Ogden and Colonel Oliver Spencer, at Elizabethtown, N. J., in 1784, was probably a good example of the original type. That consisted only of forty or fifty oblong boxes, without cover or outlet below, sunk into a bed of clay near a small stream. The boxes did duty as vats and leaches. On one side of them stood an open shed which fronted a half-dozen more boxes, the "limes" and "pools" of the beam-house, while on the other side was a circular trough, made of hewed timber, fifteen feet in diameter, in which the bark was crushed by alternate wooden and stone wheels propelled by two old horses. It was essentially a home-made plant. The wind swept through it without hindrance, and the rain and snow beat ​unchallenged upon it, hastening the decay of the vats and boxes, and giving an air of desolation to the tannery. But despite all this crudeness, as Bolles has said, and investigation tends to confirm, in this way throughout New England and the Middle States, leather, probably equal to that of any European country except England, was made even before the separation, to an extent more nearly approaching a sufficiency than any other article.
As already noted, the tanner owes more to the mechanic and machinist than to the chemist. In 1793 Deyeux, a French chemist, discovered that tannin was a peculiar body, and two years later Seguin proved that it was the active principle demanded in the operation of tanning. This led to something of a study of the properties of tannin and its distribution. In 1801 Banks, an English chemist, found that it was contained in terra japonica or catechu, and since then the list from which it can be extracted, and profitably, too, has been greatly enlarged. The use of liquor containing this active principle of hemlock or oak bark, the "ooze," as it is called, was suggested in England in 1759, but it was first rendered practically successful by Fay in 1790, and Seguin, of France, in 1795. The English had rendered their leather flexible by giving it a thorough beating with hammers by hand. Switzerland, as early as 1800, used water-power hammers, and subsequently replaced them with stamps. Berendorf, of Paris, in 1842, invented a pressing stamp, afterward supplemented by Harvey and Devergue with a roller which accomplished the same thing by passing it back and forth over the leather.
Fig. 11.—Boarding and Graining Machine.
​clayey side of a hill for its location. There was a fine spring of water just above his vats, and the natural flow of it was enough to keep them filled. Colonel Edwards's first improvement on the tannery of the day was the making of a place beneath the vats for carrying away the spent liquor. The Ogden and Spencer tannery, it will be remembered, had no provision for getting rid of
| Fig. 12.—Polishing Machine. | Fig. 14.—Pebbling Jack. |
Fig. 13.—Glossing Jack.
that refuse. Colonel Edwards, too, arranged his leaches in tiers, one above the other, and used a suction-pump for raising the liquor. He built a mill for grinding his bark, and, instead of the customary horse as motor power, used water. Perceiving that his leather tanned faster in summer, the application of heat was suggested, and the result was the invention of the copper heater. Dry hides had become very plentiful at that time, and Colonel Edwards had used a stone wheel to soften them. This, however, was a slow operation, and as an experiment the colonel took a ​few of the hides one day to a fulling mill that was near. The result of that venture was the hide mill. The work of Colonel Edwards was amplified and supplemented by others, until the leather industry had become one of the most firmly established in the country. Of these changes Mr. Pratt, to whom reference has been made, said in 1859:
"From 1815 to 1835 tanneries, which had previously been hostless though not homeless, were provided with roofs and shelter. From 1830 to 1836 we adopted several improvements in manufacturing, among which was a change in the method of unhairing the hides. Discontinuing the use of lime, we adopted, for sole leather, the process of sweating, a method which was falsely patented in this country, having been known in Pennsylvania, Maryland, and Germany. Another improvement was the substitution of fulling or softening in the hide mill in place of the old process of soaking and breaking over the beam. We also discontinued the wasteful operation of skiving, and by these improvements we succeeded in producing at less expense a larger quantity and a better quality of leather. The old method of thrashing the bark was replaced by the rotary grinding stone, and this plan in turn was replaced by the bark mill, invented by Tobey and others, worked at first by horse-power and afterward by steam and water power. As the principles of tanning became better understood, the bark was ground fine, instead of coarse, as before. The old lever pump made way for the press and screw pump; the old slicker of wood, stone, or glass gave place to the rollers made of brass. The water, also, was no longer applied cold to the bark, but heat was added to the leaches, by heaters, pan and steam, and thus the tannin was more effectually extracted. Larger leaches came into use, and the leather was put through a series of baths containing ooze of different strengths. Manual labor gave place to the more economical force of steam and water power. The change from the tanneries of the past to those of the present may be described as a change from chaos to system, from waste, confusion, and long delay, to method, economy, order, and dispatch."
These changes are represented in the hide mill, the bark mill, the splitting machine, the stuffing-wheel, the scouring machine, and the boarding machine. The hide mill was the invention, or rather adaptation, of Colonel Edwards, of Northampton, to whom reference has already been made, and the patent granted him by the Government bears the date of December 30, 1812. The next patent on this mill was not taken out until 1867, the patentee being Mr. J. M. Brown, of Boston, thus showing how comparatively few and slow were the changes in it. The object of these mills is to soften the tough, dry hides so as to render them not only easier of manipulation but readier to absorb the tannin. The mills, as ​used at the present time, vary in construction according to the grades of leather desired. Some of them are simply great drums, the interiors of which have been stuck over with rows of oak pins. In this way, when these drums are put in motion, the hides, one hundred and fifty to two hundred in number, fall upon the pins and are thoroughly beaten and their fibers loosened. The more common form of the mill, however, consists of a reservoir into which are projected a number of arms or beaters connected by rods to a shaft outside, and this latter as it revolves imparts a reciprocatory vibrating motion to the beaters. But how little advance even this is upon the ancient Egyptian fuller is apparent to
Fig. 15.—Stuffing-Wheel.
one who will take the trouble to look over some of the old prints. These show the rolls of cloth wetted and manipulated between a block and concave inclined table, with the water passing into a trough at the bottom. These all have their counterparts in the modern fulling or the modern hide mill. The hide mill was introduced among American tanners about 1830, at Salem, but it did not really come into general use, especially among the hemlock tanners of New York, until 1850. Perhaps the invention best entitled to the term "epoch-making" is that of the splitting machine. Indeed, it was the pioneer of the great improvements in the industry, and the effect of it was no other than to revolutionize the currying and finishing business in this country. Previous to its invention the tanned hides had been shaved down to
Fig. 16.—Interior Finishing-room in Upper-leather Factory.
​the desired thickness by hand, entailing obviously a great waste not only in time but in the large portions of the hide which it was necessary to throw away. By the use of these machines, however, these same hides may be split into two, three, or even five parts, of such thickness as is desired, and each part rendered available. This machine was not really perfected until about 1860. As early as 1800 rough attempts had been made to split leather by machinery, and in 1809 Seth Boyden, of Newark, N. J., secured a patent for such an invention. But there were serious obstacles which
Fig. 17.—Bark Mill.
rendered it impracticable, and it was left to the ingenious mind and skilled hand of Alpha Richardson, of Boston, to overcome them. He secured his first patent in 1831, but he continued to make improvements upon this device until 1856. Then all were grouped, and what is known as the Union splitting machine was the result. This machine is the one which is now in common use among American tanners. Its machinery is somewhat complex. It consists of a small cylinder upon which is placed the hide or leather to be split. As this cylinder turns, the leather is drawn against a sharp knife firmly bolted to the bed of the machine. Above the knife is a stiff spring which holds the leather closely to the edge of the blade, and a gauge-roller, which by means of ​screws regulates the thickness of the side, and by sectional tubes or rings serves as a friction-roller. When it is desired to split
Fig. 18.—Hoyt Spent Tan Furnace. The above illustration is from the Hoyt furnace at Wilcox, Pa. which consists of two pairs of ovens connected with three horizontal boilers. The portion in the cut consists of a section through one of the ovens and one of the boilers, showing the oven, ash pit, grate, holes for feeding the tan into the oven, the boilers, and the door to sweep out the flues.
whole hides, a still more complicated machine is employed. This is known as the belt-knife splitting machine, and was invented in 1854 by Joseph F. Flanders and Jere. A. Marden, of Newburyport, Mass. The knife in this machine consists of an endless band of steel, which revolves at a high speed, with its cutting edges close to the sides of a pair of rollers. Through these latter the leather is fed and pressed closely against the knife. The lower roller is made up of a series of rings which are capable of yielding so as to accommodate themselves to the varying thickness of the hides. The thickness of the splits is determined by a small hand-screw, by which the upper roller is raised or depressed as the case may require. The knife itself in its course of revolution comes in contact with an emery-wheel and thus is kept keen. These machines present a blade varying between fifty-seven and seventy-two inches in length, and by them an ordinary cow-hide can be split into three or four distinct parts with the utmost precision.
​It would be impossible to even enumerate the many inventions that have been made to save hand labor and hasten the various processes of finishing. Among the most serviceable is the scouring machine. When the leather is taken from the vats it is usually covered with dust and sediment and stained with resinous matter. Formerly these defects were removed by hand with brush, stone, and slicker; now, however, it is done by "scrubbers" and scouring machines. There is a variety of these, but in general they consist of a level table or platform which is freely movable in all directions. Mounted above it is a reciprocating frame, in which are fixed brushes and pieces of slate and thin stone. By the movement of this, with a small jet of water, the whole surface of the leather is scoured and brushed. Another invention—this to replace the work of the currier in paring and evening and bringing out the grain of the leather—is the whitener. Essentially this machine is like a lawn-mower. It performs its work through the cutting action of a small cylinder with sharp, oblique edges. The cylinder itself moves to and fro over the leather while the knives revolve at the rate of two thousand times per minute. In the machine invented by Mr. Charles Korn, one of the most skillful leather-finishers in the country, these knives are fastened to an endless leather belt, and are set diagonally, so that when the cut is made on the beam as it passes down in front of the operator it is a sliding one. The knives are cleared on the edge by an automatic finger and sharpened by an automatic hand. In the Union leather whitener the belt contains thirty-two knives, while the cylinder revolves 2,780 times per minute, and the pendulum swings to and from the operator at a speed of ninety a minute. These machines can do the work of from four to eight men, and do it as well. Still another finishing machine is the stuffing-wheel, by which the tallow and oil are worked into the leather. This was patented in this country in 1855 by L. W. Fiske, of Louisville, Ky., though it had been previously used in France and Germany. The crude idea of a stuffing-wheel is a revolving hogshead into which the leather and grease are put and a current of steam or heated air passed through. The success of this wheel did much to revolutionize the character of the upper leather of this country. By it the oil and tallow were worked into the center of the fiber, thus making the leather soft and yielding instead of stiff and hard as of old. These devices nearly all had their origin about the time of the civil war, when workmen were scarce in the North, and when manufacturers had to turn their attention to some means of supplying the deficiency.
Fig. 19.—Modern Tannery. Haight & Co., Ballston Spa, N. Y.
​tan. Both were economical devices. The New England tanners had long been accustomed to dry their spent tan during the summer and store it for winter use. It was then brought into service to heat liquors, and in some cases to generate steam for general tanning purposes. It was found, however, that nearly a half of it was lost in drying. The result was, that attention began to be given to the problem of utilizing it to greater advantage. In 1852 Joseph B. Hoyt conceived the idea that the wet spent tan might be burned in a detached brick furnace. He made the experiment at his tannery in Woodstock, Ulster County, N. Y. After several trials he was successful, and got from the utilization of this hitherto useless product enough power to drive his whole machinery. Since the success of Mr. Hoyt a number of furnaces have been devised for burning this wet tan. That of Mr. Hoyt, as perfected by him, consisted of two pairs of ovens, each pair being connected with three horizontal flue boilers. Each oven, with its boiler, was independent of the other, and each had a separate feed-pipe, steam-pipe, and water-tank. The only things in common between the ovens were the fire-room and the chimney. The ash-pits were the entire width of the grate, and the distance from the under side of the grate-bars to the bottom of the ash-pit was nearly five feet. This permitted a double current of air to. form in the ash-pit, the cold one entering at the front near the bottom, passing toward the back end, becoming gradually warmed by the intense heat from the grate, a part entering the oven through the grate, and the rest finally passing out of the ash-pit at the front at a temperature of 300°. By closing the furnace so as to prevent the return current, the temperature of the ash-pit could be raised to 500°. The success of these furnaces worked an immediate change in the whole tannery economy. Hitherto tanneries had been limited to the banks of streams, where they could get good water-power. Now such power was not necessary. Tanneries could be located in the open flats, where access was easy, and where the inconveniences and expenses of elevations could be avoided. Fuel was no longer an item of importance. Tanners, therefore, were not obliged to confine themselves to one great building, but they could spread out into as many smaller ones as their convenience and business demanded. They, furthermore, were no longer obliged to consider the cost of generating steam, and as a result labor-saving machinery commended itself to all. The discovery of this method of burning wet spent tan has been the determining element in the construction of the modern tannery. At the same time it has been one of the most important factors in reducing the cost of the production of leather.
From the definition of leather already given—a chemical or ​mechanical combination of gelatin and tannin or mineral salts or oil it is evident that tanned leather is not the only kind of leather. Indeed, there may be said to be three kinds, depending on the constituent elements. There are (1) tanned leather, in which the gelatin is combined with tannin or tannic acid; (2) tawed leather, in which the gelatin is combined with mineral salts; and (3) shamoyed leather, in which the gelatin is combined with oils and fatty substances. Sir Humphry Davy has distinguished between the first of these and the second and third by the statement that tanned leather is a chemical combination, its characteristic being that water will not separate its constituent elements or dissolve their connection, whereas in the case of the others it will return them to their original components. All three kinds of leather are made largely in this country. Tawed and shamoyed leather are used extensively for gloves, clothing, and domestic purposes. Some of the finer qualities have a wide use for fancy finish and ornamentation; but red tanned leather is the oldest in this country, and overtops the others by far in extent and importance, and the processes described have been those pertaining to its manufacture. And there is a wide variety in that. The heavier grades of leather, such as are used for trunks and the soles of boots and shoes, are made from the butts or the back of the hides of the buffalo, ox, and cow. The lighter grades, such as kip or upper leather, are made from the hides of young cattle older than calves and from the hides of a small breed of cattle common to India, Russia, and Africa; while all the spongy leather and morocco, or its imitation, is prepared from sheep and goat skins. These distinctions, however, are only general, but they indicate the lines along which the various branches of the industry divide. American tanners, too, have not been slow about introducing new varieties of leather. Japanned leather, used largely for fancy work and for certain styles of shoes, was first made in this country in 1818 by Seth Boyden, of Newark, N. J. In the manufacture of this the leather is first coated with a compound of linseed oil, umber, and lampblack, applied three or four times, and then is treated to a varnish made of Prussian blue and linseed oil. The leather, which had previously been stretched over frames, is afterward run into ovens heated up to 175° Fahr. Newark, too, was the original home of the enameled leather industry, David Crockett having introduced that finish. This is made much like the japanned leather, except that it is less smooth and less highly polished, the aim being to bring the grain into relief. This is used almost wholly in the coverings of carriages, and it is a branch in which America has always held the lead. Alligator skins were first tanned in Louisiana about 1855, and a considerable business has since grown up in some of the States. ​The leather, however, is to be regarded rather as a novelty than as a permanent addition to the industry. American tanners, too, have been quick to learn the methods of making the best of the foreign varieties of leather, and in some cases they have even improved on the original processes. Among these leathers of foreign origin are russia, a strong and pliant variety, generally of a red or black color, and with a peculiarly penetrating odor due to the oil of birch; and Cordovan, a small-grained, soft leather, which takes its name from the Spanish city of Cordova. It was from the gradual modification and improvement of this last that the so-termed morocco leather has resulted. This, with its brilliant colors and beautiful finish, has come to be very widely used. The manufacture of it is carried on in nearly all places where the leather industry flourishes at all, but the centers of the business are at Philadelphia, Pa., Newark, N. J., Wilmington, Del., and Lynn, Mass.
The distribution of the tanneries in this country, and as a result the centers of the leather trade, has been largely determined by the distribution of tanning materials. Tannin, the active vegetable principle of tanning, has been found in a wide variety of plants and trees. As a matter of fact, however, the only substances used largely here are the bark of the oak, the hemlock, and the sumach. Hemlock bark is found generally north of central Pennsylvania, throughout northern New York, north of Lake Michigan, and through Maine and Canada. Oak bark, on the other hand, is found abundantly in the vicinity of the Cumberland and Alleghany Mountains, and the lesser ranges of the Blue Ridge, while the sumach flourishes in Virginia and Maryland. Southern sumach, however, is not so highly esteemed as that obtained from Sicily, and much of this is imported. Some other varieties of tanning materials also are imported, like terra japonica, but the staff of the tanner in this country is the oak and hemlock. It is in those sections of the country that the tanneries are found. New York is the largest general leather market in the United States, while Boston stands close to it, especially in upper leather. Philadelphia, Cincinnati, Chicago, and Baltimore, too, are leading trade centers. The growth of the industry has been very marked since 1830. In 1850 the total product of leather in the United States was valued at $32,861,796, and the capital invested was estimated at $18,900,557. New York State stood at the head of the list, with an output valued at $9,804,000; while Pennsylvania came next, with $5,275,492; and Massachusetts third, with $3,519,123. In 1880 the value of the output had increased to $113,348,336, and the capital invested to $50,222,034. There were then 3,105 tanneries in the country. The position of the six leading States is well represented by this table:
| State | Establish- ments. | Capital. | Hides. | Skins. | Total value of products. |
| Pennsylvania | 642 | $15,608,635 | 2,970,680 | 635,280 | $27,042,068 |
| New York | 386 | 11,710,415 | 2,503,855 | 4,171,290 | 23,652,366 |
| Massachusetts | 133 | 2,712,130 | 1,625,344 | 3,724,897 | 13,536,721 |
| Maine | 83 | 2,439,700 | 879,160 | 2,202,158 | 7,100,967 |
| Illinois | 34 | 2,220,114 | 395,030 | 1,486,570 | 5,402,070 |
| Ohio | 302 | 2,022,990 | 436,015 | 434,732 | 4,357,273 |
There were, besides this, 2,319 currying establishments in this country, with a product valued at more than $71,000,000. The census figures for 1890 will undoubtedly show even larger increases in production. This increase is reflected in the importation of hides, which for the year 1891 aggregated $27,930,759. During the decade important tanneries have been started in some of the Southern States, and the industry is constantly expanding. This fact appears in the extension of the American leather trade abroad, but this is by no means what it should be. The exports of leather in 1891 aggregated $12,026,556, a gain of a little more than a million dollars as compared with the previous year. Sole leather led, with a sale of 40,084,833 pounds abroad, at a total sum of $6,430,764. It is interesting further to compare the exports of leather and the manufactures of it for the past five years:
| Year. | Value of Exports. |
| 1886 | $14,865,087 |
| 1887 | 16,235,922 |
| 1888 | 19,578,489 |
| 1889 | 23,712,814 |
| 1890 | 27,000,134 |
| 1891 | 30,736,319 |
The gain in the exports of leather, indeed, have kept pace relatively with the sale of the manufactures of it abroad, such as boots and shoes. But Americans possess certain important advantages in the making of leather that should give them a stronger hold in the European markets. The continental tanneries have no better facilities for getting hides, and they are handicapped by the lack of oak and hemlock bark which our own manufacturers have at hand. But, despite all this, the leather industry stands among the first in this country in dignity, enterprise, and magnitude. Important advances are yet to be made: but with the natural advantages of our tanners, their thrift and inventiveness, with a constantly expanding home market and a possible foreign one, there appears to be no reason why it should lose its relative rank.