GLUE, GELATINE, ANIMAL CHARCOAL,
PHOSPHORUS, CEMENTS, PASTES,
AND MUCILAGES,

COMPRISING

THE RAW MATERIALS AND MANUFACTURE OF SKIN AND BONE GLUE,
DIFFERENT VARIETIES OF GLUE, ANIMAL CHARCOAL, PHOSPHORUS,
GELATINE AND PRODUCTS PREPARED FROM IT; ISINGLASS AND
FISH-GLUE, METHODS OF TESTING GLUE AND GELATINE,
AND THE PREPARATION AND APPLICATION OF
CEMENTS, PASTES AND MUCILAGES FOR USE
IN THE WORKSHOP, LABORATORY,
AND OFFICE.

BY
F. DAWIDOWSKY,
TECHNICAL CHEMIST.

EDITED FROM THE GERMAN, WITH EXTENSIVE ADDITIONS, INCLUDING A DESCRIPTION OF THE MOST RECENT PROCESSES.

BY
WILLIAM T. BRANNT,
EDITOR OF “THE TECHNO-CHEMICAL RECEIPT BOOK.”

ILLUSTRATED BY FIFTY-NINE ENGRAVINGS.

SECOND EDITION, REVISED AND LARGELY RE-WRITTEN.

PHILADELPHIA:
HENRY CAREY BAIRD & CO.,
INDUSTRIAL PUBLISHERS, BOOKSELLERS AND IMPORTERS,
810 Walnut Street.
1905.

Copyright, by
HENRY CAREY BAIRD & CO.,
1905.

PRINTED BY THE
WICKERSHAM PRINTING CO.,
53 and 55 North Queen Street,
Lancaster, Pa., U. S. A.

PREFACE TO THE SECOND EDITION.

The first edition of this work has been out of print for some years, but nevertheless there is a constant demand for it, and this together with the fact that frequent inquiries are received for information in this department of industry, are the inducements which have led to the preparation of the present treatise.

The book is arranged in two parts, Part I. comprising Glue, Gelatine and Allied Products, and Part II. Cements, Pastes and Mucilages, and it is fully illustrated with engravings of various types of apparatus.

Since the appearance of the first edition much progress has been made in the manufacture of glue and allied products. Old and wasteful methods of working have been replaced by more approved processes, and in the present volume it has been endeavored to place before those interested in these industries, a practical and comprehensive account of modern methods of operation.

In order adequately to represent this advancement and development, the best authorities have been freely consulted and drawn upon, special acknowledgments being due to the following works: “Bone Products and Manures,” by Thomas Lambert, and “Glue and Glue Testing,” by Samuel Rideal.

As the demand for phosphorus is steadily increasing, and the manufacture of this product from bones and bone-ash forms an important branch of the utilization of bones, it has been deemed advisable to devote a chapter to this subject.

The receipts for cements, pastes, and mucilages given in Part II. have been gathered from numerous sources. They have been critically examined, and are offered, with the full conviction, that they will not be found wanting in efficacy.

The Table of Contents and Index have both been carefully prepared, and being very full, will make reference to any subject in the volume easy and satisfactory.

W. T. B.

Philadelphia, Pa., August 10, 1905.

CONTENTS.

GLUE, GELATINE, CEMENTS, PASTES.

[PART I.]
GLUE AND GELATINE.

[CHAPTER I.]
NATURE OF GLUE.

1. SOURCES OF GLUE.

The organisms of all animals, but more especially of the higher classes, contain tissues which are insoluble in cold, as well as in hot, water. However, by continued boiling they become dissolved, and yield on evaporation of the solution a glutinous, gelatinizing mass. By further drying this mass exhibits, according to the degree of purity of the material, a more or less transparent and brittle substance, which in its pure state is devoid of color as well as of smell; it swells up in cold water and dissolves by boiling in that liquid. This substance, i. e., the product of the conversion of the so-called glue or gelatine-yielding tissue, is what is known in the trade as glue.

Among the glue-yielding tissues, the following are the most important: Cellular tissue, the corium, tendons or sinews, the middle membrane of the vasa lymphatica and veins, the ossein or organic matter of bones, hartshorn, cartilage, the air bladders of many kinds of fishes, etc.

Neither glue nor gelatine exists ready formed in the animal organism, except under abnormal conditions as a phenomenon of disease, but they are the products of various transformations. The first of these transformations evidently takes place in drying the hide, since the result of boiling to glue a green hide prepared in the usual manner by liming, etc., but not previously dried, will be an entirely different product of less consistency than that obtained by drying the hide after liming and then boiling. A second transformation seems to take place in boiling the material, and a third in drying the jelly obtained, and this may explain the fact that the latter, which is not converted into actual glue, differs in its behavior from glue solution. The series of transformation does not end even with the actual glue, for it is a well-known fact that glue dissolved in water and boiled for some time does not gelatinize on cooling, but remains liquid. We have here to deal with organic combinations which are distinguished from the more solid organic compounds by passing more readily into decomposition. However, it is an established fact that glue is an organic combination presenting itself in different modifications. In the animal organism it occurs ready formed only under abnormal conditions as a phenomenon of disease, and hence it is only produced by first drying and then by continued boiling of the glue-yielding substance, and finally by evaporating and further drying the gelatinous mass obtained by boiling.

2. TRANSITION STAGES OF GLUE.

We therefore distinguish:

a. Glue-yielding substance.

b. Crude glue.

c. Jelly.

d. Glue.

a. The glue-yielding substance of the animal body is produced from proteïne substances, albumen, fibrine and caseïne, in a manner similar to that in which new substances are formed in the ripening fruit by the transformation and disintegration into constituent parts of others previously present.

b. By crude glue are understood glue-yielding materials free from all foreign matter and physically prepared by drying. It forms an intermediate link between glue-yielding substance and jelly.

This distinction between glue-yielding substance and crude glue is justified by experience. If, for instance, fresh calves’ heads, such as the tanner cuts off after swelling the skins, be carefully limed and then boiled without previous drying, the result will be a turbid liquor containing, though everything be dissolved, no jelly whatever, or at least, very little.

c. Jelly is obtained by boiling the crude glue. Its adhesive power is far less than that of solution of finished glue, and it will become more quickly putrid than the latter.

d. The finished product glue is, in most cases, not a definite chemical compound, but a mixture of substances, with two of which scientific research has made us thoroughly acquainted.

3. CONSTITUTION OF GLUE.

Independent of impurities and accidental constituents, glue consists of two distinctly distinguishable combinations, namely, glutin or gelatin and chondrin, the former being formed from the hide and osseous parts, and the latter from young bones while still in a soft state, and the “permanent” cartilages, such as those of the ribs and joints.

The manufacturer has it, of course, in his power to allow either of these substances to predominate in his product, but since experiments have shown glutin or gelatin to possess much greater adhesive power than chondrin, it is advisable to separate as much as possible the cartilaginous matter from other glue-yielding material.

As an accurate knowledge of these constituents of glue is of great importance to the manufacturer, brief reference will here be made to what scientific research has made known to us in regard to them.

Pure glutin or gelatin is obtained by treating buckshorn, etc., with water containing hydrochloric acid, until the phosphate of lime which serves, so to say, as a frame for the glue-yielding substance, is dissolved, and the organic tissue called collagen or ossein, remains behind. After freeing the latter from fat by steeping in milk of lime and careful washing, it is boiled, and the resulting jelly, when cold, mechanically distributed in cold water, in which it softens but does not dissolve. By thoroughly stirring the mass the glutin yields its coloring matter to the water, the latter being replaced by fresh water until all the coloring matter is extracted. Then pour off the water and after dissolving the jelly in hot water, filter the solution through a cloth. By mixing the filtered solution with an equal volume of alcohol, a precipitate of pure glutin is obtained. By the precipitation with alcohol, the separating glutin carries down inorganic salts, especially phosphates, which may be present in the solution. To free it from them, dissolve it in a small quantity of lukewarm water, acidulate the solution with hydrochloric acid and bring it into a dialyser. The salts and the acids diffuse in the water which has from time to time to be renewed, and finally a jelly of pure glutin remains behind; this is evaporated to dryness in shallow vessels.

Pure glutin, in a dry state forms a glassy substance, almost colorless, transparent to translucent, brittle or slightly elastic, free from odor and taste, and remains unchanged in the air. Its specific gravity is greater than that of water. It is neutral, exerts no influence whatever upon vegetable colors and is insoluble in alcohol, ether, hydrocarbons or oils. In cold water it swells up, absorbing as much as 40 per cent., and becomes opaque, but does not dissolve. It dissolves in hot water and on cooling forms a jelly even if the solution contains only 1 per cent. of glutin. It gelatinizes at a lower temperature than chondrin.

An aqueous solution of glutin is precipitated by chlorine, platinic chloride, tannin and alcohol, but not by hydrochloric acid, acetic acid, lead acetate, alum and ferric sulphate. Concentrated sulphuric acid decomposes glutin, forming, besides other products of decomposition, chiefly glycocoll and leucine.

When heated, glutin softens, swells and diffuses an odor of burnt hartshorn. In the air, it takes fire with difficulty, smokes, flames only for a few minutes, and leaves a bulky charcoal difficult to incinerate, the ashes of which consist principally of calcium phosphate.

Glutin, when in the jellied state, and treated with alcohol, undergoes dehydration, under the influence of which it contracts greatly. It was by this means that Gonnor succeeded in reducing in a remarkable degree the size of a print obtained in a very hydrated film of glutin, and transferring it, so reduced, to stone, from which he obtained a new impression, quite similar to the first, but more or less diminished.

By taking these prints, on the contrary, with glutin very little hydrated, and afterwards steeping them in water, a dilatation of the plate is obtained, which enlarges the figures with the same regularity.

Pure chondrin is prepared by boiling for from 24 to 48 hours the cartilages of the ribs, of the larynx with the exception of those of the epiglot, or of the windpipe and the bronchi.

Chondrin is precipitated from its solution by alcohol. The precipitate is redissolved in warm water, evaporated, and dried. It forms a semi-translucent mass of a slightly yellow color and resembles glutin as regards fracture and all external properties, but differs from it in being precipitated from its aqueous solution by mineral acids, acetate of lead, alum and ferric sulphate, and also by organic acids such as vinegar, citric and oxalic acids, none of which precipitate glutin.

As regards its chemical composition, chondrin is poorer in nitrogen than glutin, and contains more sulphur. Its formula approaches more closely that of albumen, which corresponds also with the origin of chondrin, for cartilages may be considered as transition-links between the proteïne and glue-yielding substances.

By the action of concentrated sulphuric acid upon chondrin, leucine is only produced but no glycocoll. By potassium hydrate chondrin is converted into glutin and yields then, like the latter, leucine and glycocoll. By boiling with concentrated hydrochloric acid chondrin is decomposed; a peculiar variety of fermentable sugar, to which the term chondroglucose has been applied, being formed.

It may finally be remarked that chondrin possesses less adhesive power than glutin and its presence in glue may be considered detrimental. To avoid its formation, the glue manufacturer should separate as much as possible cartilages from bones. Chondrin, however, is useful for size.

4. PROPERTIES OF GLUE AND ITS BEHAVIOR TOWARDS OTHER SUBSTANCES.

The product designated by the general term glue, is always a mixture of glutin, chondrin and other substances not yet accurately determined. Glue is formed by evaporating and further drying the jelly, and its properties depend on the crude glue and glue-yielding material used for the production of the jelly.

It may here be remarked that even if the quantity of glutin contained in the different products could not be determined by scientific means, the glue obtained from various materials can be readily distinguished by external characteristics. Every manufacturer knows that hides and bones yield a distinct quality of glue as regards adhesive power, elasticity and fracture, and that the jelly from glue-yielding substances of older animals is more solid and gives a larger yield than that obtained from the tissues of younger and weaker animals. Glue from the bladders and scales of fishes, though consisting mainly of glutin, differs materially from hide or bone glue.

Generally speaking, the jelly, no matter whether consisting of glutin or chondrin, possesses, before drying to glue, different properties from glue solution. It has less adhesive power and spoils more quickly. At a temperature of 68° to 72.5° F., jelly putrefies inside of 24 hours, smells of ammonia, and decomposes, while glue solution can be kept much longer without suffering deterioration.

The jelly absorbs ozone with avidity and is decomposed by it, this being the reason why an approaching thunderstorm may cause great damage by destroying the coagulating power of the glue liquors, or causing the glue to turn on the nets, i. e., to lose its consistency and become liquid and foul.

The behavior of glue solution towards different salts also deserves attention.

By adding potassium or sodium carbonate, neutral potassium tartrate, Rochelle or Epsom salts to a lukewarm fluid containing 15 to 20 per cent. of glue, the latter coagulates by the salt withdrawing the water from it. A lukewarm solution saturated with common salt, sal ammoniac, saltpetre, or barium chloride does not gelatinize.

By adding to glue solution a large quantity of alum, the glue is precipitated as a transparent mass.

Glue compounded at a high temperature with dilute acids, does not gelatinize by itself, but will do so on adding common salt.

Boiling with slaked lime deprives glue solution of its power of gelatinizing, and, on evaporation, changes it into a colorless gummy mass which is soluble in cold water and in saturated solution of common salt.

From a glutin solution compounded with oxalic acid, the latter can after some time be again separated by the addition of lime, the result being a non-gelatinizing fluid which, however, possesses great adhesive power. This is the so-called meta-gelatin.

Glue solution also loses its property of gelatinizing by repeated boiling and cooling (for about six days).

Tannin enters with the jelly, as well as with glue solution, into characteristic combinations which are formed even in solutions containing only 0.005 per cent. of jelly or glue. Glue is, therefore, an excellent agent for the detection of tannin.

When quite concentrated glue solution is treated with tannin, a heavy, flocculent precipitate of a dirty-yellow, caseous character is formed, which turns brown on exposure to the air and, after drying, constitutes a hard brittle mass, easily reduced to powder and soluble in hot potash lye, but insoluble in water, ether and alcohol. This precipitate, if not identical with, is closely allied to the combination of tannin with skin, called leather.

Glue exposed to a dry heat melts, diffuses a strong disagreeable odor of burned horn and leaves behind a charcoal which has a powerful discoloring effect like animal charcoal. When subjected to destructive distillation, glue yields an aqueous solution of ammonium carbonate and a thick brown oil consisting of a mixture of ammonium carbonate, sulphur, ammonium cyanide, etc.

The chemical composition of glue is such as to bring to mind that of starch and cellulose derived from the vegetable kingdom. It contains:

Carbon 49.1 per cent.
Hydrogen 6.5 per cent.
Nitrogen 18.3 per cent.
Oxygen and sulphur 26.1 per cent.

which may be represented by the formula: C₁₂H₁₀N₂O₄.

The composition of glue differs but little from that of the glue-yielding substance. Isinglass is composed of:

Carbon 49.5 per cent.
Hydrogen 6.9 per cent.
Nitrogen 18.8 per cent.
Oxygen 24.8 per cent.

This justifies the assumption that glue in its various transition stages does not represent different chemical combinations, but only modifications of one and the same combination distinguishable from each other by physical characteristics, as is the case with starch, which without suffering an alteration in its composition, appears as dextrine and grape-sugar, or as with cellulose, which, without altering its composition, can be transformed into amyloid and grape-sugar.

[CHAPTER II.]
USES OF GLUE.

An inquiry into the various technical uses of glue must be of interest to the manufacturer so as to enable him, when acting, as is frequently the case, as salesman, to know to whom to offer his product; and also to learn what special demands he has to satisfy, as not every glue is adapted to every purpose, different qualities being required for special uses.

Glue as a joining medium. In Chapter I, treating of the nature of glue, special attention has been drawn to the fact, that the adhesive power of glutin is greater than that of chondrin; and that glutin obtained from skin and tendons possesses still greater adhesive power than the product from bones. This is the reason why good sound glue made from scraps of skin is preferred by those artisans who may be considered the principal consumers, such as cabinet-makers, carpenters, turners, instrument-makers, wood-carvers, carriage-builders, brush-manufacturers, bookbinders, paper-manufacturers, etc., all of them requiring glue of the greatest possible adhesive power. It must, however, by no means be understood that a good quality of bone glue cannot be used for the same purposes; because much bone glue of excellent quality and at a low price is brought into the market by manufacturers of animal charcoal and bone meal, and is used in glueing wood, etc.

Glue suitable as a joining medium for the above purposes should be of an amber or brown-yellow color, transparent or translucent, clear, dry and hard, and show a glassy fracture which should not be brittle, but somewhat elastic. Placed in cold water it should swell up and absorb as much of it as possible without actually dissolving, even if it remains there for 48 hours. The supernatant water should be free from a putrid odor and contain but a small quantity of foreign substances in solution. Such glue passes into solution at 122° F., and dissolves entirely on heating to 144.5° F. Heating to a higher temperature should be avoided.

Glue as a binding agent. Glue solution is used for bind-together pulverulent substances, such as mineral colors in the manufacture of colored paper and paper-hangings, in painting in distemper, in the size of the gilder; or it is mixed with plaster of Paris or chalk for the manufacture of plastic masses which become hard on drying, such as stucco-work, papier-maché, etc. Generally speaking, it is best to use only good sound glue for these purposes, though it may sometimes be possible to utilize defective and cheap qualities without injurious consequences. For color mixtures, the glue should at all events be free from acids and alkalies, as they exert a decomposing and altering effect upon the colors. The gilder should always use the best quality of glue, as otherwise the work he applies later on to the size will spoil.

A very large quantity of glue is consumed in the manufacture of matches, and much depends on its quality and drying properties. The dipping composition for matches containing phosphorus is a bath of glue of 25 to 50 per cent. strength to which the requisite amount of an oxidizing agent, like potassium nitrate or chlorate has been added, kept at a temperature of 100.4° F. The phosphorus is cautiously put in; it melts, and is stirred to an emulsion, when the sand, glass or other friction-agent is incorporated. The object of the glue is to protect from oxidation, without diminishing the sensitiveness. Glue is also used as the binding material in the heads and rubbers of safety matches.

Book binders require for the better classes of work a glue which should naturally be pale and strong, and without marked odor. Some inferior glues which have been chemically bleached turn almost black in the pot, owing to the bleaching agent not having been properly removed or neutralized.

Sand, glass and emery papers and cloths are made by coating the surface with a thin uniform layer of strong glue, and sifting the powder evenly on.

Glue in sizing. The principal object of sizing goods is to impart to them a certain degree of stiffness, to give them a nice appearance and a good feel.

As glue would injure the color of white goods, it cannot be used for sizing them, but, on the other hand, much is employed for preparing size for the use of hat and cloth manufacturers, weavers, etc. Before the introduction of the paper machine and invention of rosin glue, animal glue was exclusively used for sizing paper, but at the present it is only used for sizing paper manufactured from rags, and for pasteboard, and also by manufacturers producing drawing paper sized with animal substances. The paper, after leaving the machine, is passed through a glue solution and then dried in the air.

For actual sizing purposes good and fine varieties of glue are only used, or sometimes the manufacturers prepare their own size by boiling to glue dried calves’ heads, or rabbit skins deprived of their fur, scraps of parchment, etc. For cheap woollen hats, glue is used in place of shellac. The cloth manufacturer procures his glue mostly in the form of a jelly. This variety of glue deserves special attention and the mode of preparing it will be referred to later on.

Glue for culinary and medicinal purposes. The use of glue for these purposes is based upon three properties:

1: Upon its power of coagulating and inclosing while in this state, substances mechanically dissolved and finely divided in a fluid, which, being specifically as heavy as the fluid itself, render the latter turbid and cannot be got rid off by settling. The glue in this case acts as a clarifier.

Large quantities of isinglass and gelatine, specially prepared for the purpose, are used for clarifying and fining beer, wine and other liquids, as well as for preparing jellies. The material to be used for jellies and other culinary purposes must, of course, be colorless and entirely free from odor. Jellies are made palatable by flavoring with spices, sugar, essences, etc., before congealing, A vegetable gelatine, Agar-Agar, which will be referred to later on is now brought from China, and being cheaper and perfectly free from odor, has become quite a competitor with isinglass and gelatine.

Prior to the introduction of Liebig’s and other beef extracts, bouillon tablets, consisting of a mixture of bone-jelly, meat broth, extract of pot herbs and flour, were largely used. One hundred and ten pounds of meat repeatedly boiled yield five pounds of bouillon tablets. A good meat broth, though not equal to that from Liebig’s or other meat extracts, is obtained from these tablets by the addition of thirty times their weight of water.

If glue be dissolved in water, it gelatinizes at the ordinary temperature, and if the solution be mixed with other fluids, for instance, meat broth, fruit juices and essences, which in the form of jelly are to serve as food, it effects their solidification.

Glue acts as a healing agent by preventing the access of air to wounds. Court plaster is prepared from gelatine. When cabinet-makers cut themselves, they apply glue to the wound with the best success. In hospitals a compound of gelatine and glycerine is used as the best means of closing wounds, the same compound having also been successfully used for preserving articles of food such as eggs, fruit, and even meat.

Every good quality of glue can be used for the above purposes.

Medicines of a disagreeable taste are frequently inclosed in gelatine capsules, so that they can be taken without causing inconvenience to the patient. The use of these capsules has grown to such an extent as to form a special branch of industry. The mode of manufacturing them will be described later on.

Glue for elastic masses and as a partial substitute for rubber. Glue mixed with glycerine forms an elastic mass resembling rubber. The same effect can be produced by an addition of molasses. This elastic mass, the preparation of which will be described later on, is of great importance for the manufacture of printers’ rollers, for moulds, etc. Some manufacturers prepare the mass ready for use, so that the printer or lithographer need only remelt it, and cast it in a mould.

Glue is of great importance in photolithography as, mixed with chromium salts, it is the only known means of transferring a photographic negative to the stone. In photography, gelatine is used for negative pictures upon glass. For the manufacturer of casts of plaster of Paris or cement, this glue mass, which is generally used without an addition of glycerine, is indispensable for making moulds which are much undercut.

Glue mixed with glycerine may be used as a substitute for rubber in manufacturing elastic toys, such as dolls’ heads, animals, etc. For these purposes it is advisable to select glue which forms a very solid jelly, even if it possesses but little adhesive power, pure bone-glue being the best.

Glue mixed with glycerine (1 part glue, 1 part glycerine) is used as hectograph mass for the transfer of matter written with concentrated solution of aniline color.

Glue for fancy articles. Great progress has been made in the use of glue and gelatine in the manufacture of fancy articles.

The best known of all these products are perhaps the gelatine foils. They form thin, transparent sheets, brilliantly colored, and are used for printing sacred images, visiting cards, labels, etc.

Gelatine veneers were first shown at one of the Paris International Exhibitions. They consist of sheets varying in thickness, which have been deprived of their translucency by an admixture of colors in imitation of various crystallization of salts, and such stones as lazulite, malachite and avanturine. Glue imitations of mother of pearl, tortoise shell, and ivory were shown which closely resembled the genuine articles. These veneers have been largely introduced in the manufacture of fancy articles, cabinet ware, buttons, etc. The most brilliant use to which they have been put is in the manufacture of fans, for which ivory and tortoise shell were formerly used, and there are perhaps few ladies that are aware that these glittering toys are manufactured from horse bones from the knacker’s yard.

The successful introduction of gelatine veneers was soon followed by a substitute for horn in general, and combs, buttons, snuff-boxes, and hundreds of other fancy articles have been manufactured from these imitations.

In the foregoing statement only some of the principal uses of glue have been enumerated, and there can be no doubt that with an increase in the knowledge of its nature and properties, a wide field is still open for progress in this industry.

[CHAPTER III.]
RAW MATERIALS AND THEIR PREPARATION FOR THE MANUFACTURE OF GLUE.

The raw materials used for the manufacture of glue consist of a variety of animal offal. The principal substances employed are refuse from tanyards, such as scraps of ox and other thick hides, the waste of the workshops of leather dressers, morocco leather manufacturers, etc. The tendons and intestines of many animals, rabbit and hare skins deprived of their fur, cat and dog skins, scraps of parchment, waste of turners and button makers, and offal from butcher shops and households, help to swell the series of materials used for the manufacture of glue.

The materials are collected and sold either directly to the glue boiler, or to dealers making a specialty of glue stock.

As a thorough knowledge of these waste products is of importance to the manufacturer, this chapter will be devoted to their detailed description, the success of the enterprise depending largely on the selection of the raw materials and their careful sorting and preparation. By bearing in mind the varied products—from the most ordinary black glue to the colorless glassy gelatine for photographic and culinary purposes—it will be understood that entirely different raw materials have to be employed for the finer products than for the ordinary qualities of glue.

According to their derivation the raw materials may be divided into three groups, namely:

1. Skin-like raw materials: Skin, leather, tissues.

2. Bone raw materials.

3. Materials obtained from fishes: Air bladders, scales, etc.

1. ANIMAL SKIN.

Fig. 1.

This consists of three layers, namely: 1. The thin upper-skin—the epidermis—which consists only of cellular tissue, and is of no special importance for the manufacture of glue. 2. The actual leather-skin, or corium, which consists of fibres of connective tissue and forms the actual object of the tanner as well as of the glue boiler. Underneath the corium lies the under-skin, which consists only of cellular tissue contaminated with particles of flesh and fat, which are detrimental to the manufacture of glue. Fig. 1 represents a section of the animal skin. O, is the epidermis, L, the corium, U, the under-skin. The epidermis consists of two layers. The first, superficial one, H, is known as the cuticle or lamellar layer, and the other deeper layer, S, as the mucous or malpighian layer. The corium also consists of two layers, the upper one C, and the lower one C₁, which is the actual leather-skin. The under-skin, U, is an elastic tissue containing many deposits of fat, F, and perspiratory glands, D, which are connected with ducts, D₁, with the surface of the skin.

For the manufacturer of leather and glue, the corium is the only material of value.

The tanner trims the skins before steeping them in the ooze. From sheep and calf skins he removes the head portions, it being more advantageous to use them for glue stock. He also cuts off the skin covering the lower part of the thighs, and, to give the skin a neat finish, the ragged edges of the belly part. Of bullock hides, the ears, tails and foot pieces are utilized for glue stock, while the head parts are tanned. Such tannery waste may yield 44 to 46 per cent. of glue. Scarf skin of bullocks’ hides and waste in fleshing the hide, tendons and hinder parts of cattle yield from 30 to 35 per cent.; horse sinews from 15 to 18 per cent.

Scraps of parchment and bullocks’ feet are highly valued as glue stock, since they are in fit condition for boiling without further preparation. They may yield up to 62 per cent. of their weight in glue.

Calf and sheep skins yield a superior glue; that from horse hides is usually dark and poor in quality, although with careful working a strong product can be obtained from the latter.

Of great value to the glue boiler are the so-called calves’ heads, which, after liming and drying, form a special article of commerce.

Skins of hogs, hares and rabbits yield a light-colored glue of little consistency. It is, therefore, best to use these last-named raw materials for the preparation of jelly, such as is used in sizing, in the manufacture of paper, etc.

The older the animals from which the skins have been derived, the more solid the glue will be. In many cases, especially where a certain quality of glue is to be produced, it may be recommended to separate the different kinds of skin refuse into lots, provided there is enough of each kind to boil it separately.

A considerable number of skins used for packing various articles, such as indigo from South Africa, have been so much damaged in transit as to render them useless for tanning, but they form good material for glue, frequently yielding 50 to 55 per cent.

In reference to judging glue stock some valuable notes are given in an article on glue, published by the American Provision Co., Chicago, Ills.:

“Dry, uncured or salted stock, such as raw hide or South American, if soaked for twelve hours in cold water, gains about 50 per cent. in weight, and still remains tough, and the water sweet. The moisture, dirt, and salt should not be over 10 per cent.

“Green salted stock, such as hide pieces, sinews, calf heads and pates, should have no excess of salt, nor be foul, discolored or heated; should be tough, with the hair not loose, and have a mild animal odor. Moisture and salt not over 40 per cent.

“Dry limed stock soaked twelve hours develops a characteristic odor, and should be firm, fibrous, and have no slimy pieces. The water should not be dark. Lime, sand and dirt, not over 5 per cent.

“Green limed stock should be smooth and soft, any remaining hair being easily detachable, while the liquor should be fairly clean, sweet, and not too alkaline.

“A large quantity of waste bones accumulates in the preparation of tinned provisions. If these have not been overheated and are in good condition, a considerable amount of glue can be obtained from them, the bones of the head, ribs, and feet giving a better yield than those of the thighs and legs.

“Horn piths should not contain over 12 per cent. moisture, and should not have been overheated in drying; they should have been cleansed from skin and hair, which are of little value to the glue-maker.

“The age of the animals yielding glue stock has an important influence on the product. While from younger animals the product, as a rule, is of lighter color, more abundant and more easily obtained, it contains more chondrin, so that from solutions of equal strengths, those from mature animals will be found to be of greater consistence and the glue more solid.

“Abroad, dry hides are often, for weighing, soaked in chlorbarium, a solution of barium chloride, and then in a bath of dilute sulphuric acid, 1½ per cent., which readily soaks in, combines with the barium to form the white insoluble powder of barium sulphate, leaving weak hydrochloric acid in the fibre, to be afterwards neutralized in liming, the chloride of calcium dissolving out. This treatment affects considerably the subsequent making of glue, as, beside the effects of the acids, the sulphate of barium will render the liquors cloudy and difficult to clarify. Of course if colored glues are to be made this will be no detriment.”

To prevent putrefaction, which is always accompanied by decomposition of glue-yielding substance and consequent loss, the scraps must be carefully preserved, especially in summer.

The tanner prepares the waste by liming, i. e., steeping it during fifteen to twenty days in milk of lime which is frequently renewed. By the action of the lime, adhering particles of blood and flesh are dissolved and the fatty matter is saponified. After this treatment the glue-stock is dried.

In case this work is not done carefully in the tanyard, as is only too frequently the case, the stock is of but little value to the glue-boiler.

By allowing the refuse to lie too long in a heap, as is sometimes done, putrid fermentation sets in, the injurious effects of which cannot be remedied by subsequent liming, or the lime bath has not yet been strong enough, or has not acted sufficiently long upon the scraps to destroy the adhering particles of blood and flesh. The lime bath, on the other hand, may have been too strong, so as to attack the glue-yielding substance. Frequently it is also the case that the scraps having been dried under unfavorable circumstances, mould has commenced to form, and finally they may be spoiled in winter by allowing them to freeze. Frozen glue leather yields glue of very little consistency.

It will be seen from the foregoing that great precaution and care are required when buying glue leather. The manufacturer should especially see that it is dry and tough, free from mould and all organic and inorganic substances, and not too strongly limed.

The glue-boiler should, in all cases, be prepared to undertake the preparation of the glue stock himself. The following arrangements are required for the purpose:

Let us assume that the glue factory is located on a stream of water. In the immediate neighborhood of the stream a sufficient number of pits to prepare all the glue stock used, each about 6½ feet deep and 6½ to 10 feet in diameter, and lined with cement, are so arranged that their bottoms are about 3 to 3½ feet above the level of the water. They are supplied with water by means of a pipe line connecting one with the other. Each pit is provided with a discharge pipe to draw off the dirty water.

As the glue-stock, before undergoing other operations, has to be freed from the lime by washing with water, the simplest plan is to place the limed stock in nets or wicker baskets suspended in running water by means of a traveling crane or other contrivance erected on the bank of the stream. This elementary method, however, is open to several disadvantages, as it fouls a large volume of water and may lead to legal interference, and its very simplicity is apt to lead to neglect of precautions, such as brushing away solid particles of lime or softened animal matters. Further, the great quantities of water carry off small pieces of glue-stock and fat, if catch-basins are not provided sufficiently large to allow fat, glue-stock, hair and lime to separate from the water.

The object is better accomplished and in a shorter time by the use of a washing drum. This consists of a perforated iron cylinder about 6 feet in diameter and 4 feet in length, and open on both ends. Around the inside of the cylinder are fixed a number of wooden shelves 6 inches broad, which, as the cylinder revolves, carry the glue-stock partly round, ultimately falling to the bottom again, the movement dashing it about under a spray of water. In the cylinder is also arranged an iron plate supported by stays from the outside. While the washing is in operation the plate is turned perpendicular; on completion it is brought to a horizontal position, forming a table, on which the glue-stock falls, and the latter is then removed to a hand-press to squeeze out the water. The washed stock is then removed to the drying ground, which should be in a sunny and airy location, and provided with an inclined floor of planks or cement so arranged as to allow of the admittance of air from beneath.

As it is well known that small quantities of liquid, frequently renewed and thoroughly drained off each time, effect the most complete and economical washing, and in the shortest time, S. Rideal recommends the use of pits or vats with proper arrangements for stirring, draining and inspection. The lime scum from the pits can be used in the manufacture of fertilizers.

The glue-stock washer shown in Figs. 2 to 5, is the invention of W. A. Hoeveler (American patent), and it relates to the construction of apparatus for washing glue-stock.

In apparatus for this purpose the stock is very commonly damaged by being broken up too much, and considerable loss results, besides, from the fact that the small particles are allowed to escape with the wash-water. By the present construction and arrangement these defects are remedied and other advantages derived.

Fig. 2 is a transverse vertical section on line x-x of Fig. 3 of this apparatus;

Fig. 2.

Fig. 3 is a longitudinal vertical section of the same;

Fig. 3.

Fig. 4 is an enlarged plan illustrating the screen and hinged covers, one being opened and one closed; and

Fig. 4.

Fig. 5 is a detail of the hub, stems and part of one paddle.

Fig. 5.

The apparatus is constructed in the form of a rectangular trough-like structure, with its sides and ends, A, substantially water-tight by means of the double walls, a a. The upper portion of the interior is occupied by the swinging wash-box, B, semicircular in shape, with flat sides and rounded bottom throughout, the bottom being perforated.

Upon a transverse shaft, c, journaled at the axis of box, B, is set a paddle-wheel composed of a suitable hub, d, and adjustable paddles, each composed of the radial stem, e, and the blade, f, or spoon. The spoons, f are set on the stems, e, so as to be capable of being reversed or turned half-way round, more or less. One side of the spoon, f, is rounded off, so that while passing through the stock the latter will not cling to or remain upon it. The other side of the spoon is flat, but slightly skewed or bevelled, so that when turned to face with the direction of motion of the wheel it not only gathers up the stock and holds it till out of the box, B, but upon further elevation causes it to roll or slide along the paddle to a predetermined point, where it falls off gently into a discharge-spout, g, which carries it off for further treatment practically undamaged. During the operation the box, B, and the body, A, are kept supplied by a stream of clean or chemically-prepared water, and the wheel, e f, revolves slowly in the box, the edges of the paddles sweeping around, while the box, B, or its bottom, is kept oscillating, thus preventing an injurious clogging of the perforations in the box-bottom. After the stock is placed in the box, B, and the latter filled with sufficient water, the wheel, e f, is caused to slowly revolve (by motive or hand power), with the rounded sides of the spoons, f, presented forward. This operation thoroughly agitates and cleanses the stock, while the rounded form of the spoons prevents the breaking up of the natural condition of the stock. The inventor gathers the finer particles as follows, after they have escaped through the perforated bottom of the wash-box, B. At the lower part of the trough, A, elevated on crossbars or blocks, h, he places two parallel strips, i, and between these, which are grooved to form ways, k, inside, is set a long screen, l, placed on rollers, m, and movable thereby on the rails or ways, k. To give movement to the screen, l, the inventor attaches to its end a rod, n, which projects outwardly through the walls, a a, by means of the packing-box, p, and cap or door, q, which, when opened, allows the withdrawal of the screen, l, and its burden. The shaking of the screen is accomplished by a suitable motor applied to rod, n, and is kept going during the operation as required. To the strips, i, which are placed at a little distance from the side walls, a (to leave a passage for the water and refuse to go through), are hinged the two doors, r, which shut down upon the rod, s, as a support, in which case nothing can fall upon the screen, or which open up and rest against the sides, a a, in which case the screen is exposed and the side passages closed by the doors, r. During the initial or rough-washing stage the doors, r, are kept closed, and the dirty water and refuse pass freely down the side passages and out at a suitable opening at the bottom. After this stage it becomes desirable to catch the particles which get detached from the stock in box, B, and come through the perforations therein. Then open up the doors, r, thus closing the side passages and compelling all the water and small stock to go to the screen, l, which catches the remaining stock. When sufficiently accumulated the screen may be drawn out and the stock thereon removed. When the main body of stock in box, B, has been cleansed, the paddles or spoons, f, are reversed, so as to present their flat, skewed faces to the stock, and in revolving the paddles now gently lift the stock and discharge it into the spout or hopper, g. The washing and removal of the stock when washed are thus accomplished without further manipulation than to reverse the paddles, which obviously could be done by a reversing-gear on the motor, thereby reversing the direction of movement of the paddle-wheel.

Instead of the whole box B being oscillated back and forth, its bottom may be set on slides or rollers and oscillated, while the sides remain stationary.

In the drawings the box B is shown as hung upon the shaft c as a centre; but as the provision of means of reciprocating or oscillating the box or its bottom is within the skill of any machinist, it is not necessary to describe any specific form. As the box with its contents will be very heavy, the inventor prefers a special motor for it, which may also be geared up to reciprocate the screen l.

Instead of the door q, as located in Fig. 2, it can be located as at q’, same figure.

The entire plant must of course be arranged according to sanitary regulations, especially as regards river pollution, etc.

The sheds for sorting and storing the glue-stock should, if possible, be in close proximity to the pits and washing drums, and be dry and airy. In arranging his plant, the glue manufacturer must, in short, exercise his ingenuity with a view to carrying on the business with as little loss of material, and as much saving of time and labor as possible.

The work in a factory arranged in the above manner, is carried on as follows:

The raw materials brought by the dealer are weighed, and if in green state, the customary percentage—generally 50 per cent.—taken off. To facilitate future operations, and to enable the manufacturer to produce different varieties of glue, the dry materials are sorted and stored in different compartments of the store-shed.

Green waste, i. e., such as has not been limed must be taken in hand at once, as otherwise it would taint the air, be attacked by rats and other animals, and suffer injurious alterations by decomposition. The manner of operation is as follows:

Liming. Prepare “milk of lime” by filling the pits, which are to serve for the reception of the skin waste, with the required quantity of water and dissolve in it 2 per cent. of calcium hydrate obtained by slaking a good quality of quick lime. Stir thoroughly, and in order that the water may become thoroughly saturated with the lime, let the liquor stand for 8 or 10 days before placing the waste in it. The liquor should stand about 9 inches deep over the waste in the pits. The length of time the waste has to remain in the milk of lime varies according to the material; calf skins requiring 15 to 20 days, sheep skins 20 to 30 days, and heavy ox hides 30 to 40 days. The milk of lime should be renewed once or twice a week, and thoroughly stirred.

For the purpose of liming, the quality of the lime used is of the utmost importance, the milk of lime being frequently quite valueless by reason of having become carbonated or a bad quality of quick lime having been originally employed. It should be borne in mind that only the hydrate of lime which is present in solution in lime water is of use, whereas in milk of lime so much carbonate and other impurities may be present that the liquid, though thick, may be quite useless. The value of a lime should always be tested by determining the amount of real calcium hydroxide, Ca(OH)₂, contained in it. The operation according to S. Rideal, is conducted as follows: Water free from carbonic acid is first prepared by boiling distilled water for half an hour in a strong, round-bottomed Bohemian or Jena flask. While steam is still issuing, the flask is removed for an instant, closed by a well-fitting greased cork or a rubber stopper, and allowed to cool. When the temperature has somewhat fallen, the cooling may be cautiously accelerated by dipping into a pail of warm water, then transferring to the cold stream from a tap. The water may be preserved in the flask or, preferably, a number of bottles with vase-lined stoppers should be filled quite full and retained for use.

From the sample of lime, well mixed, a small portion (about 0.25 gramme) should be accurately and rapidly weighed, placed in a wide-mouthed, stoppered bottle holding about 300 cubic centimeters, 250 Cc. of the boiled water added, and then allowed to settle. The whole of the calcium hydrate will now have dissolved. Fifty cubic centimeters of the clear liquid should now be withdrawn by a pipette, transferred to a flask, colored with an indicator—either phenol-phthalein, methyl-orange, or litmus may be used—and its alkalinity determined by running in decinormal hydrochloric or sulphuric acid from a burette till the change of color occurs. Each cubic centimeter of the acid corresponds to 0.0028 gramme of calcium oxide, or 0.0037 gramme of the hydrate, Ca(OH)₂. The amount by calculation will give the percentage of real lime present in the sample. It is well to notice that any soda or potash present will equally neutralize the acid, and be returned as lime, but as these are of almost equal efficiency their presence in small quantity has no disadvantage. For special work it will be necessary to have a full analysis. As a rule the product made from limestone, or “stone lime,” is the best article in commerce, and is much more free from stones and clay than “gray lime” or “shell lime.” The best stone lime contains sometimes only ½ per cent. of impurities, and seldom more than 5 per cent., while inferior kinds of gray lime may contain as much as 50 per cent., and would be of little use in glue-making.

After removal from the lime pit, the material is placed in willow baskets or nets, and immersed in the stream to remove the greater portion of the lime, which is generally effected in a few days. It is still more effectively accomplished by placing the waste, after soaking in the willow baskets, in the wash drums. After taking it from the baskets or wash drums it is spread in the drying yard to drain and dry, the desiccation being accelerated by turning it over with a fork several times a day. While drying, the quick-lime is converted into carbonate, the latter exerting no disturbing effect in the manufacture of glue. When sufficiently dried, the material is ready for boiling, and the crude glue thus obtained can be stored for any length of time, until wanted for further manipulation.

In summer it is scarcely possible to cleanse the raw material as rapidly as it is brought to the factory, and to work it immediately without putrefaction setting in, and for this reason it would frequently be risky to purchase larger quantities of it, even if offered at very favorable terms. During the colder season of the year, drying of the cleansed raw material is such a slow operation, that in order to prevent putrefaction, recourse would have to be had to artificial heat.

These drawbacks can, however, be overcome by the use of carbolic acid, which possesses in a high degree the property of preventing putrefaction. It is quite cheap, and as but a comparatively small quantity of it is required, the additional cost need scarcely be taken into consideration, since the value of glue-stock annually destroyed by putrefaction is considerably greater than the expense for carbolic acid.

The raw material is thoroughly cleansed, and while in a moist state is gradually brought into a brick cistern or large vat, carbolic acid solution being poured over each layer, so that, when the cistern or vat is filled, it stands about an inch or two deep over the material. The latter may be left in this state until wanted.

The carbolic acid solution is prepared by dissolving 2 lbs. of carbolic acid in 1000 quarts of water; the fluid thus obtained possessing a slight odor of smoke. The washed glue-stock treated as above described with carbolic acid remains absolutely unchanged, and when wanted needs only be taken from the cistern and worked like fresh material.

In plants having no running water at their disposal and depending entirely on well water, and where the waste water has to be discharged into rivers or creeks, water containing carbolic acid should be used for all the washing operations, a fluid containing 1 to 2 parts of carbolic acid in 10,000 parts of water being sufficient for this purpose. Such an addition of carbolic acid prevents the wash-water from becoming foul.

Carbolic acid has the tendency of hardening the glue-stock and imparting its odor to the glue, and among other antiseptics, formaldehyde and boric acid have been recommended for the purpose of preventing putrefaction for a reasonable time. Formaldehyde in weak solution (1 part in 10,000 to 100,000 parts water) has been found beneficial. In this small quantity it does not harden the stock nor affect the subsequent boiling, as it is dissipated by the heat. Boric acid and its preparations, notwithstanding their low antiseptic power, are much in favor. A fluid containing 1 part boric acid in 200 parts water will have to be used.

The principal varieties of hides and leather for glue-stock may be classed as follows:

1. Bullock leather from old animals, highly limed, mixed with rump pieces, also with horse leather, the latter being thin, of a dark color and soft, and is of less value than bullock leather, because it yields a dark glue. Fat leather is bullock’s leather from fat, stall-fed cattle, and before use has to be freed from fat (by means of benzine).

2. Pieces of hide from the lower parts of the limbs of cattle, not limed and with the hair; they form excellent glue-stock, yielding a very adhesive glue.

3. Worn-out hinges from weavers’ looms, consisting of strongest untanned bullock’s hide. When treated with lime they yield a very strong glue, but are worked with difficulty.

4. Whip leather. This is waste in the manufacture of whips, and is derived from thick tawed bullock hide. It yields an excellent, light-colored glue.

5. Calf leather. Broad, thin, translucent strips, slightly limed, yields glue of a very light color.

6. Calves’ heads. The skin of calves’ heads, limed, without hair. They constitute the best material for gelatine, and form a special article of commerce.

7. Calves’ feet. The skin from the last but one leg-joint which is cut off from dry, unlimed, haired skins. It is the best material next to calves’ heads.

8. Knapsack leather. Old knapsacks of calf skin and waste in the manufacture of new ones, tawed with the hair on with alum and common salt. When suitably washed this yields good glue-stock. The alum and common salt have to be completely removed by washing. The hair is no detriment to the process of boiling, it serving as a filter for the glue running off. To this class belong also all kinds of fur waste, especially remnants of old fur coats (sheep skin coats), from which the wool is removed and the skin used as glue-stock. All these materials having been treated with alum and common salt have to be freed from them by suitable manipulation.

9. Hare and rabbit skins freed from their fur. They yield a light-colored glue of little consistency.

10. Cut rabbit skins. In depriving these skins of their fur, they are cut by a machine into fine threads of even size. In France they are worked into size for gilders’ use which is highly valued.

11. Sheep and lamb leather (goat leather) limed, thin and very light, yields but a small quantity of glue of little consistency. To this class belongs the waste in the manufacture of kid gloves. Waste of morocco and other varieties of similar leather, pressed into bales and secured with wire, comes into commerce under the name of Levant leather.

12. Waste obtained in paring kid leather and in the manufacture of gloves. It constitutes a flocculent powder and yields very thin glue liquor with slight adhesive power. Before boiling, the substances used in tanning must be completely removed by washing.

13. Surrons. These are untanned, unlimed skins of various wild animals (antelopes, gazelles) which have been used for packing leaf tobacco and various drugs. They form good glue stock.

2. BONES AND CARTILAGES.

In addition to hides, bones are a material highly valued by the glue boiler. Chemically speaking, the framework supporting the fleshy tissues of the animal order, and which we call bones, is a combination of phosphates of lime and magnesia, carbonate of lime, and alkaline salts, united with fatty and cartilaginous matter. To the latter we look for our yield of glue; to the fatty matter for the fat, and to the phosphates for the basis of fertilizers.

Bone cartilage is composed of carbon, hydrogen, oxygen and nitrogen, the percentage composition being practically constant, whether the cartilage be from an old or a young animal. The bones of the young are, however, much richer in cartilage than those of the old. This is reversed in the case of the inorganic or mineral matter, the old having the greatest yield of phosphates.

Then again, the fatty matters are more in evidence in full-grown animals than in youth or age; also in the thigh and leg bones the yield is higher than in the heads, ribs or shoulder blades, the latter averaging 12 to 13 per cent., whilst the former runs 18 to 19 per cent.[1]

[1] Bone Products and Manures. By Thomas Lambert. London, 1901.

Bones being less subject to putrefaction than skin-stock, they are not brought into commerce in a prepared state. They are mainly bought by contract from various dealers within easy access to the works. The rates are generally fixed for a certain period, and cover all classes of common bones, whether fresh butchers’ or a mixture with partly boiled bones. Bones differ considerably in their value. A fresh bone will yield the highest percentage of fat and glue. On the other hand, partly boiled bones may contain only 6 per cent. fat with 30 per cent. water. In buying bones the manufacturer should exercise great care, as the dealer sometimes finds ways and means of including hoofs, horns, iron, beefy matter, and even pieces of brick. Naturally they form weight, but, excepting the horns, have no value.

To separate the different classes of bone coming into the works, and arrange them according to the amounts they would produce of fat and glue, is no doubt a desirable object, but in practice it is seldom carried out. However, if the manufacturer wishes to undertake this tedious work, it is recommended to make the following distinctions:

1. Bones of young animals, sheep, calves, dogs, cats, etc., being readily disintegrated, are thrown into one pile, and also the light bones of oxen, such as skull bones, shoulder bones, the vertebra of the tail, etc.

2. A second pile is made of the foot bones of goats, sheep and cattle, provided they can be had, as is the case in the United States and England, in sufficiently large quantities.

3. Scraps and shavings from bucks’-horn from turners and button-makers.

4. Thick bones of oxen, horses, etc., which must remain longer in the lime-bath, together with waste of hard bones from turners.

5. Where large quantities of bones are handled it is advisable to sort out the bones of the upper thigh, as they can be more advantageously used for the manufacture of piano-keys, handles for tooth-brushes, etc. Hoofs, which are frequently found, should be thrown out, as they yield no glue and can be utilized for other purposes.

The further manipulation of the bones for the manufacture of glue requires first of all their crushing or grinding in a stamper or mill. By this crushing or grinding of the bones two objects are attained, namely, they are more readily deprived of their fat and present more points of attack to the corrosive agents to be used later on. The crushed bones are put in a large boiler, and for a few hours subjected to the action of steam. Leg bones, as well as horns, should not be boiled, as they contain no fat, and would lose too much glue-yielding substance. After boiling, the bones are placed in a lime vat for 8 to 14 days. The water used for boiling the first portion of bones may be used for a second one.

The extracted fat amounting to 4 or 5 per cent. of the quantity of bones used, is taken off the surface of the cold liquor and the latter may be utilized as a fertilizer, or fed to cattle.

For crushing the bones, a stamping mill is generally used, it yielding, when properly constructed, material for the manufacture of glue, as well as granulated bones which form an excellent product for the preparation of animal charcoal.

Since animal charcoal in pieces of quite even size is now in general demand, it is recommended to manipulate the bones in the above-described manner, to sell the granules to the manufacturer of animal charcoal, and use for boiling glue only the completely-crushed portions and the porous bones which are not at all suitable for the manufacture of animal charcoal.

Fig. 6.

Fig. 6 shows a stamping mill very suitable for the crushing of bones, the illustration showing the mill open on the left side and closed on the right. It is furnished with 16 stamps, D, each stamp being provided with a cast-iron shoe. The stamps are lifted by means of a cam shaft in such a manner, that the height of fall of the outermost pairs of stamps is least and that of those in the centre greatest. Between the inner stamps is a sieve H with meshes of sufficient size to allow the largest pieces, which can be produced by granulation, to fall through.

Underneath the sieve is an Archimedean screw K for carrying off the pieces of bone passing through the sieve.

Fig. 7.

Fig. 8.

The base of the stamping mill consists of iron plates so arranged as to form steps, the plates lying towards the center of the mill constituting the lowest steps. Every two stamps standing alongside one another rest upon such a step. When the mill is set in motion, the bones reaching the stamping trough from the right and left fall upon the steps, and are crushed by the descending stamps.

As a rule, the bones to be stamped are not brought directly into the stamping trough, but are first passed through a crushing mill and the coarser pieces thus obtained are subjected to the action of the stamping mill.

Figs. 7 and 8 show a well-constructed bone crusher. It consists essentially of two cast-iron rollers A and B, furnished with case-hardened cutters. The bones are introduced through the hopper B, and the rolls set in motion by means of cog-wheels a and b. The bearings of the roll B run in a carriage which can be shifted by the lever-construction f i. The object of this contrivance is to allow of the roll B giving way in case a harder material than bones, for instance, a stone, passes between the rolls.

Fig. 9.

The Crosskill bone mill, Fig. 9, as described by S. Rideal, is intended to be driven by a strap from the fly wheel of a common portable engine. It consists of a pair of strong rollers made of wrought-iron with case-hardened cutters, and a revolving or oscillating riddle for separation of the ground bones as they fall from the cutters; the whole carried by a substantial cast-iron frame. The mill will grind from 6 to 16 hundred-weight per hour with a three to eight horse-power engine.

For sorting the crushed bones into pieces of equal size, a sieve, Fig. 10, is used consisting of a drum constructed of narrow boards covered with wire-netting of different degrees of fineness. The upper portion A of the drum consists of narrow-meshed net and through this falls the fine meal which is conveyed by the Archimedean screw F over the frame F G H into vessels serving for its reception.

The lower section, B, of the drum is furnished with netting, the meshes of which become gradually wider towards the lower end, and, hence, the smallest particles of bone fall through the funnel, D, the medium-sized ones through E, and the largest ones through F. Pieces which cannot pass through F, leave the drum at G.

In factories manufacturing glue as well as animal charcoal, the larger pieces are steamed by themselves to obtain their fat, and then charred, while the small pieces and the meal are utilized for glue.

Fig. 10.

The lime-bath used for bones should be of the same strength as that for skin-stock. After removal from the lime vat and washing, the bones are put in a tank of stone or wood (brick pits should not be used) containing cold hydrochloric acid of 70° Bé. or 1.05 specific gravity (= 10.6 per cent. HCl) for thick bones, or half that strength for thin bones, and are thus left to digest for 8 to 14 days, being frequently stirred and fresh acid added. By the action of the acid the calcium phosphate is dissolved and the bones become cartilaginous, flexible and transparent. The phosphates can be precipitated by ammonia, or the whole evaporated with charcoal or silica, and distilled to make phosphorus.

When sufficiently softened, the stock is washed in wicker baskets or a washing drum to remove adhering acid. They are then placed for one day in the lime liquor, again washed, and then either dried or stored away for future use, or boiled at once to glue, while in a moist state.

Leg bones, horns, and other soft bones which contain scarcely any fatty matter are not steamed for the reason previously stated, but in all other respects are treated like steamed bones.

It is of the greatest importance that the bones should be thoroughly freed from acid, since even the smallest quantity remaining behind exerts an injurious effect upon the finished glue. It is therefore recommended to test the water draining off, or the bones themselves, with litmus. If the tincture turns red, it is a sure indication of the presence of free acid, and the washing must be continued until the blue color of the tincture remains constant.

Gerland’s suggestion, to use dilute sulphurous acid in place of hydrochloric acid for dissolving the phosphates of the bones, and to evaporate the sulphurous acid by heating, whereby the phosphates are precipitated in an insoluble state, has now been quite generally introduced.

For the preparation of gelatine from bones, Jullion and Pirie’s process may be recommended. It requires a somewhat expensive plant, but saves hydrochloric acid and time. The process consists essentially in dissolving the phosphates of the bones in vacuum. A box of wood, or better of granite, which can be closed air-tight, is required for this purpose. The box is filled with bones, and acid of the previously-mentioned strength poured over them. The box is then closed and the air pumped out by water or steam power. The smallest cracks and pores of the bones are thus freed from air, and the latter is replaced by hydrochloric acid, which in this manner acts rapidly and is completely exhausted. The remaining crude glue is then further worked in the usual way.

Bones honey-combed by putrefaction, exposure to the weather, or burial in the ground are of little or no value to the glue-boiler, as nearly all the glue-yielding substance has been destroyed; they should therefore be thrown out in buying stock. The ammonia which is formed when putrefaction sets in, colors the glue dark.

3. LEATHER WASTE.

Leather tanned with a substance insoluble in water is not directly suitable for manufacturing glue, but can be made so by a special process, which, though somewhat tedious, nevertheless pays for the trouble.

In using such stock the manufacturer should make a distinction between old and new leather. The principal materials of this kind, large quantities of which contribute their quota to the glue-boiler’s stock, are old shoes, straps, harness, etc., and further, waste from shoemakers, trunk-makers, and in fact from the shops of all workers in leather except those using alumed leather.

Before boiling the leather waste to glue, the removal of all traces of tannin becomes absolutely necessary, since the retention of the smallest quantity prevents the animal tissue from dissolving in water.

The various methods proposed for the preparation of the leather waste differ either in the chemical solvent used, or in the mechanical manipulation of the waste.

The principal point in all methods is to comminute the waste as uniformly as possible to facilitate the complete removal of the tannin.

Various machines, some very complicated, have been proposed for the comminution of the waste, but a rag engine or “hollander” such as is used by paper-makers deserves preference for the purpose, as it not only comminutes, washes and prepares the waste in a suitable manner for the manufacture of glue, but the leather pulp when mixed with rags or woody fibre gives a substitute for leather which is very tough and of good appearance, and can be worked into many articles.

After the preparation in the hollander and careful washing the waste is treated, according to Stenhouse, under a pressure of two atmospheres in a boiler with water to which is added 15 per cent. of the quantity of waste to be treated at one time of slaked lime.

By another method the extraction of the tannin is effected by boiling the leather pulp with caustic soda of 1.025 specific gravity for from six to twelve hours. After drawing off the water and pressing out, the pulp is again boiled with caustic soda of the same concentration. The next process is to carefully wash out the soda, which is best effected in the hollander.

By neutralizing the soda lye in the fluid drawn off after the first boiling, it can be re-used for tanning or purposes for which tannin is required.

According to another method, the modus operandi is as follows:

Dissolve 1½ lbs. of oxalic acid in 3 gallons of water, pour the boiling solution over 110 lbs. of waste, and keep the mixture in a water-bath at a temperature of 176° to 212° F. This effects the solution of the pulp. Then dilute the solution by adding gradually 4 gallons of water until a uniform mass is formed. Now add 5 lbs. of lime slaked to a thin paste, and mix the whole thoroughly. The mass becomes friable and pulverulent. It is passed through a wire sieve and then exposed to the air. In three to four weeks the tannin is entirely destroyed, which is recognized by the mass assuming a lighter color. The lime is then removed by washing with water and hydrochloric acid. If the tannin has not been entirely destroyed by exposure to the air, add 1 lb. of liquid ammonia and a like quantity of pyrolusite to every 110 lbs. of leather substance when boiling it to glue. The oxygen yielded up by the pyrolusite, which, in the presence of ammonia, exerts no injurious effect upon the glue, destroys the last traces of tannin. Frequent stirring with a shovel while the material is exposed to the air and moderate heating, facilitates the destruction of the tannin.

4. RAW MATERIALS FOR FISH GLUE.

The air-bladders or sounds of various fishes contain much glue-yielding substance and on account of its purity, the product known as isinglass obtained from them is preferably used for culinary and medicinal purposes. The high price of the raw material excludes it from being used by the glue-boiler, but as he manufactures substitutes for isinglass, and should therefore have a thorough knowledge of the article with which he has to compete, its manufacture will be included in this treatise. Since, however, the work of the manufacturer is finished with the preparation of the raw material, i. e., of the air-bladders into crude glue, isinglass and its substitutes will be referred to later on.

There is a material difference between isinglass and glue manufactured from entire fishes. The raw material is, of course, limited to certain localities. The principal point to be observed in the manufacture of fish-glue is the removal of the skin, which is effected by means of dilute sulphuric acid.

After removal of the last traces of acid, the fatty matter of the fishes is saponified by a treatment with milk of lime frequently renewed. After washing out the lime, the pulpy mass is placed in a solution of sodium hyposulphite, alum, and common salt, where it remains for a few days. The liquor is then drawn off and replaced by a mixture of solution of alum, dilute sulphuric acid and nitric acid. After macerating in this mixture for a few days, the mass is thoroughly washed and boiled to glue, and the resulting product clarified with sulphurous acid or alum solution. As will be seen, the entire process is tedious, requires many chemicals, and besides the yield of glue, which has no specially good qualities, is small. It is used as a substitute for isinglass for clarifying liquids. The best proof that the business is of but little importance is found in the fact that no fish-glue has been exhibited at any of the late international exhibitions.

The scales of large fishes, such as carp, give more favorable results. They are treated with hydrochloric acid in a similar manner to bones. The scales do not dissolve entirely, a horny insoluble mass, giving no glue, remaining behind after the solution of the glue-yielding substance.

[CHAPTER IV.]
MANUFACTURE OF SKIN GLUE.

The thorough preparation of the raw materials will materially facilitate all succeeding operations, which may be classified as follows:

1. Boiling the glue.

2. Clarifying the glue-liquor.

3. Forming or moulding the glue.

4. Drying the glue.

However, before entering into the description of these operations, it will be necessary to refer to an intermediate product, which has been previously mentioned under the name of crude glue, and is prepared, for instance, by tanners and manufacturers of parchment, but also forms in some localities a special branch of industry.

This crude glue is actually not glue, but a glue-yielding substance in such a state of preparation that it can be directly used for the first operation, namely, boiling. It consists of waste of skins and leather of all kinds, completely cleansed, dried and limed, and in the case of leather treated with agents for the extraction of the substances used in the tanning. As will be readily understood, the operations required for the preparation of this stock are virtually the same as those described in the previous chapter for raw materials and need not further be here referred to.

The bulk of such stock is prepared by tawers and manufacturers of parchment, though a considerable quantity of it is also derived from waste in the manufacture of gloves. The product from the latter source is also found in commerce under the French names Colle franche or Brochette. However, if such stock is used, it is best to again immerse it in lime water, after which it should be thoroughly washed.

The manufacture of glue from hide and leather waste differs materially in many respects from that of bone glue, it being the more simple process, as no other preliminary operations than the preparation of the glue-stock are required. The first operation is

1. COOKING OR BOILING.

For this operation any kind of boiler may be used, but the materials should be supported on a perforated grid a little distance above the bottom, so as to save them from risk of scorching. In the centre of the grid stands a conical pipe 2 to 3¼ feet long, perforated like the grid and communicating with the space between the grid and the bottom of the boiler. The height of the boiler can be increased 1 to 1½ feet by placing an annular piece upon the rim which is bent upwards for its reception.

The size of the boiler depends on the quantity of raw material to be worked at one time. It is best to choose boilers holding from 110 to 440 lbs. of glue-stock, and to place two, four or more of such boilers in one hearth.

The manner of using such a boiler is very simple. Straw is placed upon the false bottom in such a manner as to cover its entire surface, and extend up the sides of the boiler at least as far as it is touched by the flame. The object of the straw is to serve as a filter, and protect the materials from injury by the flame. But for the production of entirely pure gelatine or glue, straw cannot be used, as, by boiling, it yields a yellow coloring matter, which passes into the glue. Barley straw gives a less intense coloring matter than rye straw.

In case straw cannot be used, the material is placed in a large bag, previously thoroughly boiled, and suspended in the boiler so as not to touch the sides. By this means scorching is prevented even if the fire touches the bottom as well as the sides of the boiler.

The boiler having been heaped with material so high as to overflow the brim and fill the annular piece placed upon it, is filled with water as far as touched by the fire. The fire may now be started. The hearth in which the boiler is placed should, of course, be so constructed that the gases are uniformly distributed and the water quickly brought to the boiling-point. When the water commences to boil, bubbles of steam ascend from the space beneath the grid and, passing through the perforations of the conical pipe, penetrate the glue-stock. Thus the first formation of glue takes place, and the stock begins to settle down gradually as it goes into solution. The stock heaped up in the annular piece also sinks down gradually, and being partly heated by the hot vapors and thus prepared for solution, is finally submerged in the boiling solution and becomes soon entirely dissolved.

Waste of hide and horn piths are completely dissolved in five to seven hours. No more water should be used than is absolutely required for cooking the entire quantity of stock, because too much water renders the solution too thin and gives a jelly of little consistency and difficult to dry. Concentrating the glue solution by continued boiling is bad practice, as it is detrimental to the resulting product by reason of the glutin undergoing a gradual transformation.

It is best to start with a slow fire to give the stock time to soften and thus prepare it for solution. When somewhat softened, the mass is brought to boiling and the latter kept up, gently and uniformly, until solution is complete. Solution is promoted by careful stirring, but care should be had not to disarrange the straw upon the grid and on the sides of the boiler as this would interfere with proper filtration of the glue solution.

The duration of cooking depends on the nature of the raw materials. Scraps of skin from young animals, antlers, sheep trotters, etc., dissolve in three to four hours, while waste from ox and horse hides, or bones from old animals, require six to eight hours.

The progress of the operation is readily ascertained by pouring a small sample of the gelatinous fluid in half an eggshell, and setting it aside for a few minutes to cool. If a clear and consistent jelly be obtained, boiling has been carried on to a sufficient extent, and the liquid is drawn off. Any undissolved glue-stock remaining upon the straw filter can be boiled by itself, and the resulting gelatinous liquor utilized in the next boiling.

It is evident that quick and uniform solution of the materials, which enhances the quality of the glue, is promoted by comminuting the glue-stock either by grinding, stamping, or mechanical means.

The succeeding clarification of the glue is much facilitated by removing while boiling the scum, consisting of fat, coagulated albumen, lime-soap, accidental admixtures, and other impurities. Before drawing off the gelatinous liquor it is advisable to withdraw the fire and allow the contents of the boiler to rest for fifteen minutes.

The residue remaining upon the straw filter consists of hair, lime-soap, undissolved particles of hide and bones, lime, etc., and is utilized, after repeated boiling, as fertilizer or for the manufacture of gas.

The mode of glue boiling above described is the oldest and at present is only in use in small establishments. Fig. 11 represents a convenient apparatus for the purpose. It consists of three boilers upon as many different levels. The lower boiler, b, serves for the settling and clarification of the glue. It communicates with the second boiler, a, which contains the material to be acted on, by means of a pipe provided with a stopcock, and is sufficiently heated by a small fire to keep the glue liquid without allowing it to reach ebullition. The upper boiler, c, which is heated by the waste heat of the chimney, serves as an economical reservoir for hot water. The end of the discharge-pipe of the settling boiler is provided with a filter of woven wire. As the sides and bottom of the second boiler are lined with straw, which acts as a preliminary filter, the glue runs off quite clear from the settling boiler.

When this mode of manufacture is adopted, two boilings can be made per day, under favorable circumstances, so that, if the boiler has a capacity of 220 lbs. of stock, which will yield from 110 to 132 lbs. of dry glue, the daily fabrication will be about 220 lbs. of finished product.

Fig. 11.

In larger plants, the above described mode of extracting the glue-stock with water has been superseded by the use of steam in a cylindrical wrought-iron boiler, twice as high as wide, and capable of withstanding a pressure of three atmospheres. The boiler is furnished with a perforated false bottom underneath which terminates a steam pipe. It is filled from above with previously softened glue-stock and the charging hole hermetically closed. Steam is then gradually admitted and exerts at once a dissolving influence upon the stock. A portion of the steam condenses and forms with the dissolved glue-stock a concentrated jelly which collects between the true and false bottoms.

For the escape of air a cock is provided which is closed as soon as steam commences to escape from it.

Fig. 12.

The advantages of this process are obvious. A larger quantity of glue-stock can be extracted than in the boiler previously described, and there is no danger of injury by scorching and consequent damage to the color of the glue. More highly concentrated solutions are obtained in a shorter time, and the spoiling of the glue solution by too long continued cooking is prevented by drawing off the solution as quickly as formed. The escaping hot vapors may be utilized for drying the glue, softening the raw material, etc., the entire quantity of heat being thus utilized. A further great advantage of this method is that there is less annoyance from badly-smelling vapors than when boiling is done over an open fire. A number of such boilers can be arranged in one room and supplied from a common steam boiler.

Fig. 12 represents a boiler for extracting glue-stock with the use of steam. It is provided with a lid, D, which is removed for charging the boiler. The aperture, E, in front, serves for the removal of the residue. Above the true bottom there is another false bottom, perforated and movable, which can be covered with straw for preliminary filtration. The steam reaches the glue-stock through a pipe which passes through the actual and false bottoms, and is perforated above the latter. The resulting jelly collects between the true and false bottoms, where it is less exposed to the action of hot steam. The escaping steam passes through the pipe, F, which is provided with a stock-cock. The pressure in the boiler is indicated by the manometer, K. After throwing the materials into the boiler they can be covered with warm water, or, after the lid is closed, warm water is introduced from a reservoir through a special pipe and distributed over the material through a rose.

The boiler stands upon a frame sufficiently high to allow of conveniently placing a vessel under the pipe G, through which the jelly is discharged. The vessel, when full, is conveyed to the settling vat, or the arrangement may be such that the jelly is directly run into the settling vat.

In many large plants open jacketed pans heated by steam are still used for treating the material. Fig. 13 shows an arrangement with two of such pans; of course one, or a larger number may be used, according to requirement. In the illustration the pan I on the left is shown in front view, and the pan II on the right, in section. K₁ is the actual pan enclosed by the jacket K. Steam circulates in the space between pan and jacket, whereby the stock in the pan is heated. K₁, in addition, is furnished with a steam coil S, which may, however, be omitted.

The steam enters through the pipe D, the space between pan and jacket, passes into the coil S, and escapes at b. The water formed by the condensation of steam in the space between pan and jacket, as well as that which runs off at b from the coil S, is carried away by the pipe A.

The pipe L serves for conveying hot water to the pans, and the pipe F for the discharge of the finished glue liquor. The stirrer R, is furnished with two paddles, and is set in motion by a transmission on the ceiling of the room. It serves for keeping the stock in the pans constantly agitated, solution being thus very much promoted.