CHAPTER VIII.

DIFFERENT VARIETIES OF GLUE AND THEIR PREPARATION.

Besides the broadly-distinguished forms of skin-and bone-glue, the trade recognizes a large number of varieties, distinguished either by their value or their fitness for special purposes.

_Joiner’s Glue._—This variety is without doubt the oldest in use and most in demand, and its principal requisite is its great adhesive power. It is used for joining wood, leather, paper, etc., and varies very much in quality and price.

The best variety is prepared from scraps of hide and skin. A light color not being especially demanded, there existing rather a prejudice in favor of a dark-colored article, waste of cattle and horse skins and tendons can be used for its manufacture.

Joiner’s glue, which is generally preferred in thin cakes, is chiefly manufactured in regular glue factories, though to be able to compete with the bone-glue turned out by the large establishments, the glue-boiler generally mixes skin and bone-glue, and is thus enabled to turn out a tolerably good quality. The price paid for the different varieties of joiner’s glue varies very much, being generally higher in winter than in summer, and is frequently more regulated by the external appearance of the article than by its actual value. Glue without gloss, very much warped and of a very dark color, may, notwithstanding its faulty appearance, possess excellent qualities.

Nothing need be said about the manufacture of joiner’s glue, since what has been said about the manufacture of glue in general suffices for the purpose.

_How to make and use glue._ Break the glue into small pieces, put it into an iron kettle, cover it with water, and allow it to soak twelve hours; after soaking boil until done. Then pour into a box which can be covered air-tight; leave the cover off until cold, then cover up tight. As glue is required, cut out a portion and melt in the usual way. Expose no more of the made glue to the atmosphere for any length of time than is necessary, as the atmosphere is very destructive to made glue.

All glue, as received from the factory, requires the addition of water before it will melt properly, and every addition of water (while the glue is fresh made) will, up to a certain point, increase its adhesiveness and elasticity. Some glues will bear more water than others, but all will bear more water than usually falls to their share, and that, too, with a greater improvement in the quality of the work. For glue to be properly effective, it requires to penetrate the pores of the wood, and the more a body of glue penetrates the wood the more substantial the joint will remain. Glues that take the longest to dry are to be preferred to those that dry quickly, the slow-drying glues being always the strongest, other things being equal. Never heat made glue in a pot that is subjected to the direct heat of the fire or a lamp. All such methods of heating glue cannot be condemned in terms too strong. Do not use thick glue for joints or veneering. In all cases work it well into the wood in a manner similar to what painters do with paint. Glue both surfaces of your work excepting in the case of veneering. Never glue upon hot wood, as it will absorb all the water in the glue too suddenly, and leave only a very little residue, with no adhesiveness in it whatever.

_Holding power of glue._ 1. Glue exerts a far greater hold on surfaces of wood cut across the grain than on those that have been split, or cut with the grain.

2. When two surfaces of split wood are laid together, the hold of the glue is the same whether the fibres are laid parallel or crosswise to each other.

3. The holding power of glue on different woods estimated in kilogrammes per square centimeter (0.155 square inch) is as follows:

Cut across the grain. Split. Beech, 155.55 (342.21 lbs.) 78.83 (173.42 lbs.) Hornbeam, 126.50 (278.30 lbs.) 79.16 (174.15 lbs.) Maple, 87.66 (192.85 lbs.) 63.00 (138.6 lbs.) Oak, 128.34 (282.34 lbs.) 55.16 (121.35 lbs.) Fir, 110.50 (243.10 lbs.) 24.16 (53.15 lbs.)

_Cologne glue._ The variety of glue known under this name is prepared from selected scraps of hide and skin, and is consequently very pure, and possesses great adhesive power. It is of a light-brown color, and comes into commerce in short thick cakes of great hardness. It is an excellent quality of glue, and is preferred to all others by bookbinders, workers in leather, etc. There are many imitations of this variety, bone-glue being frequently sold as Cologne glue.

The genuine article is manufactured from refuse of hide, which, after liming, is carefully bleached in a bath of chloride of lime, the concentration of which depends on the darker or lighter color of the glue-stock. For 220 lbs. of glue-stock, it is generally customary to use 1 lb. of chloride of lime mixed with sufficient water to cover the stock.

After thorough impregnation of the glue-stock, which generally requires about half an hour, add sufficient hydrochloric acid to impart an acid taste to the bath of chloride of lime. To be able to mix the mass thoroughly, it is best to use a vat provided with a stirring apparatus. After allowing the acid to act for a quarter of an hour, remove every trace of it by careful washing.

To obtain a jelly as clear as possible, the gelatinous liquor is drawn off as soon as the thin portions of the glue-stock and the outside of the thicker ones are dissolved, they being more thoroughly bleached than the rest. The residue is worked into darker glue.

_Russian glue._ This variety is of a dirty white color, and, like Cologne glue, is brought into commerce in short, thick cakes. Its color and opaqueness are imparted to it by an addition of 4 to 8 per cent. of white lead, chalk, zinc white, or permanent white (sulphate of baryta). It has been claimed that the superior adhesive power of Russian glue is due to this addition of mineral substances, but the results of many experiments fail to substantiate this claim. In case the glue turns out turbid, it may be of advantage to make it opaque by an addition of coloring matter, but the quality of the glue remains unchanged. The best time to add the coloring matter is shortly before drawing the glue-liquor from the clarifying vats into the cooling boxes, as the jelly is then of sufficient consistency to prevent the substances from settling on the bottom. Skin-glue, as well as bone-glue, is sold under the name of Russian glue.

Quite a considerable quantity of Russian glue brought into commerce in the form of brownish-white sheets is prepared from bones, the latter being degreased by boiling, steaming or extraction, and the solution of the mineral constituents effected by means of hydrochloric acid. The treatment with acid is, however, continued only till the bones commence to become soft and flexible. The solution of phosphates is then drawn off, and the softened bones are washed and in the usual manner worked to glue.

By this incomplete treatment with hydrochloric acid, a certain quantity of the phosphates remains in the cartilage and is inclosed in the glue prepared from it, the finished product acquiring thereby a dirty whitish color, which is by many considered an evidence of its quality. This mechanical admixture of phosphates, however, does not affect the adhesive power of the glue, neither increasing or decreasing it. Such white and opaque glue is manufactured to answer the demand in certain quarters of the trade, and, as above mentioned, heavy white substances are often intentionally incorporated with skin glue, as well as bone glue, to give it the appearance of Russian glue. These heavy powders add to the weight of the product, though when incorporated with it in small quantities do not injure its adhesive power, but large quantities render the product weaker.

_Patent glue._ This term is applied to an indefinite number of preparations, but particularly refers to a very pure variety of bone glue of a deep dark-brown color not showing net marks. It is very glossy, and swells up much in water. To satisfy the demand for thick cakes, they must be cut from very concentrated jelly to insure their drying.

_Gilder’s glue_ is found in commerce in very thin, pale yellow cakes tied up in packages weighing about 2 lbs. each. It is a variety of skin glue bleached with chloride of lime, and dissolves with difficulty in water. The first runnings from the boiler are used for its manufacture.

A very superior article of gilder’s glue is obtained by cutting rabbit skins into fine shreds and boiling in water, then turning the mixture into a basket through which the liquid passes, leaving the refuse behind. About 100 grammes (3.52 ozs.) of sulphate of zinc and 20 grammes (0.705 oz.) of alum are then separately dissolved in pure boiling water and poured into the first-mentioned liquid, and the whole well stirred together while hot. The mixture is then passed through a sieve into a rectangular box, in which the jelly remains twenty-four hours in winter, or forty-eight in summer. The solid mass is taken from the box, cut into slices of proper thickness, and dried upon nets.

_Size glue and parchment glue_ are manufactured in the same manner. Both are skin-glues, and can be readily produced by following the directions given for the manufacture of skin-glue.

_Paris glue_ is used for sizing. It is brown, opaque, and almost always soft. Being very hygroscopic, and imparting a suitable flexibility to the felt, it is better adapted for hatter’s use than any other variety. For its manufacture only the generative organs, or the thick tendons of the legs of cattle and horses, are used, or other waste and fleshy parts, and substances mixed with small bones, which, if thoroughly cleansed, might yield a good quality of glue, but are intentionally transformed by too long-continued boiling, whereby the gelatinous solution is largely deprived of its adhesive power, and yields a hygroscopic product.

_Liquid Glues._ These are chiefly combinations of glue with some ingredients added to destroy the gelatinizing property and yet not impair its adhesiveness. They remain for a long time clear and syrupy, and are used for a variety of purposes. Below are given a few receipts for such glues.

1. Dissolve 38 parts of glue in small pieces in 100 parts of acetic acid. Solution is promoted by exposing the vessel to the sun or placing it in hot water.

2. Dissolve 50 parts of light-colored glue in 50 parts by weight of hot water, in which 14 parts of fused magnesium chloride have been dissolved. The solution on cooling does not gelatinize, but remains syrupy, the density varying according to the quantity of water used. In the preparation of printing inks it can be used as a substitute for gum.

3. Dilute 10 parts of strong phosphoric acid with an equal weight of water, and then gradually add 4 parts of ammonium carbonate in the dry state. When the effervescence has subsided, add a further 5 parts of water and warm on the water-bath or steam-chest to 158° F. Now add 20 to 40 parts of glue, according to the consistency required, and stir until all is dissolved. Cool.

4. Dissolve 20 parts of glue in an equal weight of hot water, then cautiously pour in, stirring constantly, 4 parts of strong nitric acid, warm until the nitrous fumes have been driven off, filter, if necessary, through fine shavings, and allow to cool.

5. Dissolve 3 parts of glue in small pieces in 12 to 15 parts of saccharate of lime. By heating, the glue dissolves rapidly and remains liquid, when cold, without loss of adhesive power. Any desirable consistency can be secured by varying the amount of saccharate of lime. Thick glue retains its muddy color, while a thin solution becomes clear on standing.

The saccharate of lime is prepared by dissolving 1 part of loaf sugar in 3 parts of water, and after adding one-fourth part of the weight of sugar of slaked lime, heating the whole to between 149° and 185° F., and allowing it to macerate for several days, shaking it frequently. The solution, which has the properties of mucilage, is then decanted from the sediment.

The solution of the glue in saccharate of lime is readily accomplished, even old gelatine, which has become insoluble in water, dissolving without difficulty. This variety of liquid glue possesses great adhesive power, and admits of many uses.

6. Dissolve 8 parts of glue in 16 parts of hot water, then add ½ to 1 part of hydrochloric acid, and 1½ parts of sulphate of zinc. Keep the mixture for 8 hours at 158° F., then filter through fine shavings, and allow to cool.

_Steam glue._ Under this name several varieties of liquid glue are brought into commerce. They are prepared as follows:—

1. _Russian steam-glue._ 100 parts of a good quality of glue, 100 to 110 parts of warm water, and 5.5 to 6 parts of commercial nitric acid of 36° B.

2. _Pale steam-glue._ 100 parts of glue, 200 of water, and 12 of nitric acid of 36° B.

3. _Dark steam-glue._ 100 parts of glue, 140 of water, and 16 of nitric acid of 36° B.

Soak the glue in cold water, then pour the necessary quantity of warm water over it, and heat gently on a water-bath until all the glue is dissolved. Next add gradually the nitric acid with constant stirring, and to the Russian steam-glue 6 parts of finely pulverized sulphate of lead, which will impart to it the white color.

_Chrome glue._ This preparation is very permanent and durable. To prepare it add to a moderately concentrated solution of 5 parts of glue 1 of dissolved acid chromate of lime, this salt being considered better for the purpose than the bichromate of potash usually used. The glue thus prepared becomes, after exposure to the light, insoluble in water in consequence of a partial reduction of the chromic acid. This preparation can be used for cementing glass articles, liable to be exposed to boiling water, the treatment being the ordinary one of applying the glue to both surfaces of the fractured object, and then binding them together until dry, and exposing them for a sufficient length of time to the light, after which boiling water will have no effect upon them. It is suggested that this preparation is better adapted to cementing the covers on glass slides than any now in use. The same preparation can be applied for making fabrics water-proof, especially sails, awnings, etc., where no great flexibility is required. Two or three applications of the glue, either by immersion of the object in it, or by the use of the brush, will answer the purpose. Roofing paper is also rendered impervious, even when exposed to long-continued rains.

_Glue for attaching leather to metal._ A method of affixing leather to metal, so that it will split before it can be torn off, consists in digesting a quantity of nutgalls, reduced to powder, in eight parts of distilled water for six hours, and filtering it through a cloth; then dissolving one part by weight of glue in the same quantity of water, and allowing it to remain twenty-four hours. The leather is moistened with the decoction of nutgalls and the solution of glue applied to the metal, previously roughened and heated. The leather is then laid upon it, and dried under pressure.

_Glue for leather, paper, etc._ The following process affords an unusually adhesive paste, adapted to fastening leather, paper, etc., without the defects of glue, and if preserved from evaporation in closed bottles will keep for years. Cover 4 parts, by weight, of glue with 15 parts of cold water, and allow it to soak for several hours; then warm moderately till the solution is perfectly clear, and dilute it with 65 parts of boiling water, intimately stirred in. Next prepare a solution of 30 parts of starch in 200 of cold water, so as to form a thin homogeneous liquid free from lumps, and pour the boiling glue solution into it with thorough stirring, and at the same time keeping the mass boiling.

_Glue for parchment paper in making sausage skins._ The supply of intestines soon being exhausted by the enormous quantity of pease-sausages manufactured for the German army during the Franco-German war, the necessity arose for a substitute. This consisted of a tube of parchment glued together. Millions of these tubes from Dr. Jacobsen’s factory were tested by the government, and found to answer the purpose admirably. They were even boiled for hours without either the glued seam or the paper itself being injured by the operation. The secret of the composition of the glue employed for fastening the parchment paper seems to be well kept, but the one given in the following is equal to it in all respects, if not indeed identical: Add to one quart of a good adhesive solution of glue ¾ to 1 oz. of finely powdered bichromate of potash. Warm the mixture slightly on a water-bath when about to use it, and before applying it moisten the parchment paper. The latter, when glued with this preparation, as in the formation of the small cylinders for sausages, must be rapidly dried on a hurdle, and then exposed to the light until the yellow glue becomes brownish. The cylinders are then slowly boiled in a sufficient quantity of water to which two or three per cent. of alum has been added, until all the chromate is dissolved out, and they are then washed in cold water and dried, and will look very inviting, especially if white glue has been used. A similar result may be reached by using a concentrated solution of cellulose in ammoniacal oxide of copper. Thus if cylinders of unsized paper are formed with this paste, and when thoroughly dry drawn through a parchmentizing solution (a cooled mixture of 2 volumes of fuming sulphuric acid and 1 volume of water), they will be beautifully parchmentized, and after the neutralization of the acid, washing, etc., it will present a striking resemblance to natural intestines.

_Tungstic glue._ This preparation offers an acceptable substitute for hard India rubber. It is made by mixing a thick solution of glue with tungstate of soda and hydrochloric acid, by means of which a compound of tungstic acid and glue is precipitated, which, at a temperature of 86° to 104° F., is sufficiently elastic to admit of being drawn out into very thin sheets. On cooling, this mass becomes solid and brittle, and on being heated is again soft and plastic. It can be used for all purposes to which hard rubber is adapted.

_Indestructible mass for the manufacture of ornaments, toys, etc._ A mass, which is to have the hardness of horn, consists of 50 parts of glue, 35 of wax or rosin, 15 of glycerine and the required quantity of a metallic oxide, or mineral color. A soft mass consists of about 50 parts of glue, 25 of wax or rosin, and 25 of glycerine. The glue is melted in the glycerine with the assistance of steam, and the wax or rosin added. The latter in melting mixes with the glue and glycerine, and finally the mineral color is added. The mass is poured in a liquid state into moulds of plaster of Paris, wood, or metal. The degree of hardness of the mass is increased by an addition of 30 to 35 per cent. of zinc white, or other mineral color, according to the color the article is to have.

_Compound for billiard balls._ Allow 80 parts of Russian glue and 10 parts of Cologne glue to swell up in 10 parts of water; then heat over a water-bath, and when dissolved, add 5 parts of heavy spar, 4 parts of chalk and 1 part of boiled linseed oil. Of a portion of the mass form small sticks, dip them in the remainder, and allow the adherent portion to dry, and repeat this process until a crude ball has been formed. This is placed in a dry room for three or four months, and when thoroughly dry, it is turned. The finished ball is placed in a bath of sulphate of alumina for one hour, dried, and polished like an ivory ball.

_Coloring glue._ Common black or dark glue, while possessing all the adhesive and other essential qualities of fine colored glue, has heretofore, owing to its color, been confined in its use to such purposes in the arts where color was not essential.

The object of the following process, which is the invention of G. J. Lesser, of Frankfort, Germany, is to color such glue so that it is both refined and tinted, and may be used for various purposes in the arts. It is especially applicable in the manufacture of sizing and finishing compounds for paper hangings, compounds for the manufacture of elastic rolls, for glue and size compounds for finishing yarns, textile fabrics of silk, cotton, etc., for the manufacture of calcimines and wall-coverings, for glue to be used with colored woods, and for all other purposes where a fine, strong-colored glue is required.

For coloring common black or dark glue take a pound and a half of liquid extract of lead and mix it into the water in which the glue has been soaked, as follows: Thirteen pounds of glue, sixty-three and a quarter pounds of water. Allow the glue to soak for about twenty-four hours, then dilute it by a slow fire, and when heated gradually pour in one and a half pounds of the extract of lead and mix it well together.

The extract of lead is a well-known commercial article, and it is well suited for this purpose; but the inventor does not limit himself to this particular preparation, as there are a larger number of neutral and basic compounds of lead that may be so modified as to produce results similar, if not identical, with the results obtained by the formula above given. Gelatine may be treated instead of glue.

_Compositions for printing rollers._ All such compositions contain gelatine or glue. The following receipts are used:

| I. | II. | III.| IV.| V. | VI. | VII.| VIII. -------------+-----+-----+-----+-----+-----+-----+-----+-----+ Glue | 8 | 10 | 4 | 2 | 32 | 2 | 1 | 3 Molasses | 12 | — | 8 | 1 | 12 | 6 | 2 | 8 Paris white | 1 | — | — | — | — | — | — | 1 Sugar | — | 10 | — | — | — | — | — | — Glycerin | — | 12 | — | — | 56 | — | — | — Isinglass | — |1½ ozs.| — | — | — | — | — | — India rubber| — | — | — | — | 10 | — | — | — in naphtha

A patent roller composition is thus made: Gelatine 32 lbs. and glue 4 lbs. are softened in cold water and melted in a glue boiler. To this are added 4 lbs. of glucose, 72 lbs. of glycerine, and 1 oz. of methylated spirit. The whole is then digested for four to six hours and cast into rollers. This composition is claimed to be unaffected by temperature, to retain its elasticity, and not to shrink.

In practice it is found that all these compositions from the cleansing and remelting become gradually sticky and useless. To partially overcome this difficulty, formaldehyde is added to the roller composition, which renders the glue insoluble in water, and thus prolongs the life of the roller.

_Size._ This product is simply an undried glue and is used, not for adhesiveness, but as a body for filling porous surfaces, such as wood or plaster, stiffening and weighting textile fabrics, in paper manufacture, and as a foundation for oil paints and varnishes. According to Thomas Lambert, many firms who have a good selling connection for size, do not go to the expense of erecting clarifying plant and drying house for treating the glue-liquors, but prefer to stop the process half way, as it were, and marketing the resulting product as size. Others, again, with a complete glue plant at hand, convert only a portion of their liquors into size, to meet trade demands, the bulk going for the manufacture of glue. Size varies in quality to suit the requirements of different trades. Cardboard box-makers prefer a strong skin size, which is manufactured red or yellow as preferred. A strong yellow size made from bone is used by calico-printers, paper-stainers, wall-paper manufacturers, and in the straw-hat and carpet trades.

In the preparation of skin-glue, the first and second liquors are used for that purpose; the residual mass is then treated with water and steam, which practically exhausts the gelatinous matter. This, the third liquor, is used solely for size. During the boiling, samples are taken at intervals, cooled, and the condition of the jelly noted. The strength is also taken by the glue meter, which registers the percentage. At a strength of 8 to 10 per cent. the liquor is run off, passing through a filter of fine shavings or cloth, to remove any suspended matter, into a wooden vat fitted with a steam coil, then heated with a moderate charge of sulphurous acid to bring up the color, and evaporated to a strength of 36 to 38 per cent., as may be desired, and then run into casks to jelly. If skin-glue is not made, the three runnings are used entirely for size.

An outline of a simple process used in an English factory devoted to making tub-size, as given by Samuel Rideal, may be interesting.

The material is obtained from the tanyard ready limed and freed from hair, and consists mainly of “faces” of bullocks or cows, the noses being cut off as food for dogs. It is soaked again in weak lime water and re-washed, then placed in coppers made of wrought-iron wielded in one piece, and holding about 10 to 20 gallons, enclosed in outer jackets of the same material containing water which is kept well boiling. There are six coppers, about five feet high by three feet in diameter. The charge of each is about ½ cwt. The material is covered with water and well stirred with sticks for two hours, the scum and dross being occasionally skimmed off and thrown away as useless. At the end the size is ladled on to sieves, from which it runs into cooling vats, and is filled while moderately hot into clean tubs.

The liquor is clear and of a light brown color for the best XX quality, and darker for the common. The coolers or setting-backs are of wood or zinc, and the liquid is not kept hot longer than it can be helped, as it is liable to turn sour.

Bone-size is, according to Thomas Lambert, prepared as follows: The bones are first degreased by the naphtha process, and then passed through the cleanser direct into the glue-boilers and steamed, as in the manufacture of glue. The resulting liquors are forced up to the clarifying vats and partially bleached with a current of sulphurous acid, passing through bag-filters to the evaporating troughs, and concentrated from 30 to 38 per cent., as required, and then jellied in casks.

The manufacturer with no benzine or glue plant at his disposal washes the bones in a revolving drum, and, after crushing, they are fed into a boiler and subjected to an alternate current of steam and water, the latter coming from a spray pipe fixed at the top of the boiler. The liquors are generally drawn in two portions, having a strength of 14 to 16 per cent. of glue. After separating the fat, which is refined and sold to the soap-maker, the liquors are run into a large wooden vat about 8 × 6 × 4 feet, fitted with a steam coil, partly bleached with liquid sulphurous acid, and then boiled down to the required strength.

For a common size the bones are crushed but unwashed, and are fed direct into the boiler and treated as above. The liquors are not bleached, and boiled to a strength of about 25 per cent. glue. The composition of the different grades may be given as follows:

Common size. 25 per cent. glue, 75 per cent. water, etc. Medium size. 30 per cent. glue, 70 per cent. water. Best size. 38 per cent. glue, 62 per cent. water.

A concentrated size is now prepared by many manufacturers. It is a bone-size, and is sold at a Baumé strength at 122° C.

No. 1. 15° Bé. at 122° C., 40.5 per cent. glue. No. 2. 20° Bé. at 122° C., 44.5 per cent. glue. No. 3. 25° Bé. at 122° C., 49 per cent. glue.

Under the name of concentrated size also are sold a series of powdered glues of different qualities. They are the off-color and twisted cakes, sorted out in the warehouse, and ground to a fine condition by passing through a mill, and their value is based on the quality of the cake ground.

Size rapidly ferments and becomes sour and mouldy unless some preservative is added. Sulphate of zinc is mainly used for this purpose.

_Bookbinders’ Size._—I. Water, 2 quarts; powdered alum, 1 oz.; Russian isinglass, 2 ozs.; curd soap, 40 grains. Simmer one hour, strain through linen or a fine sieve, and use while warm.

II. Water, 2 gallons; best glue, 1 lb.; alum, 4 ozs. Prepare and use as above.

III. Water, 2 quarts; isinglass, 5 ozs.; alum, 240 grains.

_Water-proof Glue._—Solution of glue by itself or mixed with pigments is used in painting walls in distemper. A water-proof coat is obtained as follows: Boil 1 part of powdered gall-nuts and 12 parts of water until the mass is reduced to two-thirds of its bulk. Then strain through a cloth and apply the solution to the dry coat of distemper paint, the latter becoming thereby as solid and insoluble as oil-paint. The tannin of the gall-nuts acting only upon soft glue, the solution has to be applied so the lower layer of glue becomes thoroughly soaked through.

To render _wrapping paper_ water-proof the following glue-solution may be used: Dissolve 24 parts of alum and 4 parts of white soap in 32 parts of water in one pot, and in another 2 parts of gum arabic and 6 parts of glue in 32 parts of water, and mix the two solutions. Heat the mixture, immerse the wrapping paper in it, and pass it through hot rolls, or dry upon twine stretched in frames.

_Fabrics may be rendered water-proof_ with glue and tannin. The process is based on the fact that by the action of tannin or bichromates, compounds insoluble in water are formed. It is, however, of first importance that both solutions—tannin and glue—should fully penetrate the fabric. If the latter is dipped directly into strong solution of glue and then of tannin, the glue will only become insoluble on the outside, and that which has penetrated deeper into the fibre will be unchanged, having been protected by the superficial insoluble layer. Hence, the treatment is commenced with a very weak solution of glue, prepared by leaving glue broken small in hundred times its weight of water for twenty-four hours. By that time the glue will have swelled up, and the whole is boiled, whilst being constantly stirred, so as to get a perfectly clear solution in which the fabric is boiled for 10 to 15 minutes. This time is no more than necessary for complete penetration. The fabric is then well wrung between two rollers placed over the glue-bath so that excess of solution runs back into it. The fabric is then hung up, and when nearly dry is passed through a tannin solution. The latter may be made from tannin itself, or from a tannin extract, or by boiling galls or oak bark in water. The tannin solution can be used fairly strong, as only so much of it is taken up as corresponds to the glue present, and it can be used over again as long as it can supply the tannin required, and can then be reinforced with more tannin as required.

It is not necessary for the fabric to stay long in the tannin, as it reacts quickly with the glue. The tanned material is again hung up to dry, and when quite dry is washed in plain water to remove any excess of tannin. The whole process from the beginning is then twice repeated. After this second repetition there is so thick a layer of tannate of gelatine on the fabric that the dry cloth has acquired considerable solidity and a smoothness which recalls that of leather. The fabric is now passed through a stronger glue solution, using three or even four parts of glue per hundred of water, but never exceeding the latter limit. After the glue-bath the fabric goes through the tannin bath, whereby it becomes quite thickly coated with tannate of gelatine. By repeatedly treating with glue and tannin alternately, this coating can be made as thick as desired, and finally masses are obtained in which the texture of the fabric is entirely hidden, and especially after the fabric has been calendered under heavy pressure after water-proofing. The color acquired by goods thus water-proofed is a more or less dark leather-brown.

Muratori and Landry treat the fabric with a solution made in three separate operations:

1. Potash alum 100 lbs. dissolved in 10 gallons of boiling water.

2. In another vessel 100 lbs. of glue are soaked in cold water till the glue has trebled in weight. The remaining water is poured off, and the glue liquefied by the application of heat. When the glue is boiling, 5 lbs. of tannin and 2 lbs. of soda water glass are put in it.

3. The two solutions are boiled together, being stirred constantly.

When the mixture is complete, it is allowed to cool to a jelly. To water-proof the goods some of the jelly is boiled with water (1 gallon to 1 lb., or a little over) for three hours, adding water to compensate for evaporation, so as to keep the volume of the solution constant, as shown by tests of its specific gravity with a hydrometer. The bath is then allowed to cool to 176° F., and the fabric is soaked in it for half an hour and then stretched out horizontally for six hours to drain. The fabric must be kept horizontal, so that the solution remains uniformly distributed through it. The drainings are collected to be used over again. The fabric is then dried in the open air or in a drying room, still in the horizontal position. If a drying room is used the temperature of it should not exceed 122° F.

Muzmann and Krakowitzer dissolve 10 lbs. of gelatine and 10 lbs. of tallow soap in 30 gallons of boiling water, and mix the solution in 4 gallons of water in which 15 lbs. of alum have been dissolved. The whole is boiled for half an hour, and then allowed to cool to 104° F. At that temperature the fabric is thoroughly soaked in it, dried, rinsed, again dried, and finally calendered. In this process the alum partially decomposes the soap, forming either free fatty acid or an acid alumina soap. The gelatine forms an insoluble compound with the alum. The free fatty acid or acid soap is mostly carried down on the fibre by the precipitate formed by the alum and the gelatine.

_Glue for Joints in Leather Driving Belts._—Soak equal parts of good hide glue and isinglass in water for 10 hours, and then boil with pure tannin till the product becomes sticky. The surfaces to be cemented together should be roughened and the glue applied hot.

According to another method 2 lbs. of best glue are dissolved at a moderate heat in 3 lbs. of water and about 3 drachms of carbolic acid stirred into the hot solution. The mixture is poured into shallow iron pans to congeal, when it is cut in pieces and dried in the air. For use the glue is liquefied by adding a small quantity of vinegar and applied with a brush to the leather. The joint is finally pressed between iron plates at a temperature of about 77° F.

_Hectograph Mass._—Soak a good quality of glue for 24 hours in sufficient cold water to cover it. Then take the swelled glue from the water and melt it in an enameled pot over a moderate fire. When perfectly liquid add the required quantity of glycerine (see formulas below) and intimately mix both by continued stirring.

The vessel containing the mixture should for some time be kept hot, so that the mass remains thinly fluid. The purpose of this is to allow the air-bubbles formed by stirring to rise to the surface. If any scum is formed on the surface, remove it carefully with a shallow spoon. The composition is then ready to be poured into the vessel intended for its reception, which may be made especially for the purpose, or a shallow baking pan of tin may be used. When the pan is filled with the composition place it perfectly level in a cool place free from dust and allow to remain at least for several hours.

_Formulas for Hectograph Masses._—I. Gilder’s glue, 100 parts; glycerine of 28° Bé., 500.

The glue is allowed to swell in water, as described above, then melted, mixed with the glycerine, and evaporated to the required consistency.

II. Gilder’s glue, 100 parts; glycerine of 28° Bé., 400; water, 200.