CHAPTER IX.

MANUFACTURE OF GELATINE, AND PRODUCTS PREPARED FROM IT.

Gelatine, like glue, is produced from hides and skins, and bones. It is distinguished by its purity, has a slight yellowish tint, and is very hard and elastic. In cold water it softens, swells up, becomes opaque, but does not dissolve. In hot water it dissolves completely, and on cooling for several hours, an almost colorless, transparent and very firm jelly results. This property of becoming jellied is in part lost if the solution is for some time exposed to a temperature higher than 212° F.

The chemical constitution of gelatine is entirely changed by concentrated sulphuric or nitric acid. Concentrated acetic acid, on the other hand, renders softened gelatine transparent, and then dissolves it; the solution does not become viscid, but preserves its adhesive property. Dilute acids have no appreciable effect either on the coagulating or the adhesive power.

Tannin is a valuable and delicate test of the presence of gelatine. When added to a solution containing only 1/5000th part of gelatine, nebulosity is immediately apparent. When more concentrated gelatinous liquors are treated with tincture or infusion of nut gall, a dense, white, caseous subsidence occurs which, on desiccation, becomes brownish-yellow, agglutinates, and forms a hard, brittle mass easily reduced to powder.

Gelatine is much used for culinary and medicinal purposes, and for fining beer, wine and other liquids. Considered medicinally, it is emollient and demulcent, and for this end is dissolved in water or milk, and rendered palatable by the addition of acid and sugar. In pharmacy, it is used for the formation of capsules intended to conceal the nauseous odor and taste of medicinal preparations inclosed in them. It is likewise employed for coating pills.

SKIN GELATINE.

But few changes have been made in the process of manufacturing skin gelatine since the method introduced and patented, in 1839, by George Nelson. This patent relates to the preparation of a transparent gelatine from waste of calf skins, and of an inferior variety from other skins freed from hair, wool, and fleshy and fatty matters. The mode of procedure is the same in both cases, and is as follows: The cuttings being washed are macerated in solution of caustic soda or caustic potash at a temperature of 60° F., until they are partially softened. Ten days is the average period required to effect this. They are then placed in closed vessels and permitted to remain until a thorough softening is effected. They are now washed in a revolving cylinder, through which a current of water passes to free them from adhering alkali; exposed in a well-closed chamber to the action of sulphurous acid, and finally submitted to pressure to remove the adhering water. The softened mass bleached by sulphurous acid is then placed in a suitable vessel and subjected to the action of steam until it is, as far as possible, dissolved. The liquor is then strained and set aside at a temperature of 100° to 120° F. for the impurities which may have remained to subside. The clarified solution is poured upon slabs of slate or marble to the depth of about half an inch and allowed to remain there till sufficiently solidified, when it is cut, and washed to remove all traces of acid. It is subsequently redissolved by means of a steam bath at a temperature of 95° F., finally again solidified, and dried by exposure to dry air upon nets.

Messrs. J. and G. Cox, of Edinburgh, patented in 1844, a process by which a perfectly pure substance, superior to that prepared from isinglass is obtained. Shoulders and cheeks of ox-hides are preferred by the patentees. They are thoroughly cleansed in water, after which they are cut into pieces by a machine similar to that used for cutting straw, and then subjected to the action of a paper-maker’s pulp-mill. By this process the gelatinous fibre is well washed and cleansed, as a stream of water flows through the mill during the whole operation, carrying off all the impurities. The comminuted material is next pressed between rolls, mixed with fresh water, sufficient to effect its solution, and heated to a temperature varying from 150° to 212° F. The resulting gelatine-solution is then allowed to cool to 150° F., and mixed with fresh bullock’s blood—1 part of the latter to 700 parts of solution. At a somewhat increased temperature the albumen of the blood coagulates and rises in the form of foam to the surface, or subsides in the shape of flakes, carrying with it the impurities, and thus clarifying the liquor. The latter is allowed to stand for some time, when it is poured upon stone slabs and allowed to solidify.

G. P. Swinborne’s improved patented process for the preparation of gelatine from hides, skins and glue pieces, relates mainly to the cleansing of the raw material. The latter is reduced by means of suitable instruments to shavings or slices, and soaked in cold water, which is drained off and replaced by fresh water three times a day, until no odor or taste is perceptible. The shavings are then heated with water, not above boiling, strained through filter cloths, and the liquor is then run on to slate or other material to dry.

The modern process of preparing skin gelatine is, according to Thomas Lambert, carried out as follows: The first treatment the cleansed skins undergo is the “steeping” process with caustic soda or milk of lime. In some factories a mixture of caustic (slaked) lime and soda ash is used, in the proportion of 6 lbs. soda ash and 6 lbs. slaked lime to every hundred-weight of skins treated, the chemical change being that the whole of the carbonate of soda (soda ash) is converted into caustic soda by its equivalent of caustic lime, the excess of the latter remaining as such. The equation representing this is—

Na_{2}CO_{3} + CaH_{2}O_{2} = 2NaHO + CaCO_{3} Soda ash. Caustic lime. Caustic soda. Carbonate of lime.

This steeping is conducted in large wooden vats, each having a length of 12 feet, width 8 feet, and depth 3 feet, and fixed with a slight gradient to the overflow, which is placed at the most convenient corner of the vat and protected by perforated boards. The skins in the vat are nearly covered with water, and then the solution of caustic soda, or the slaked lime mixed in water to a cream, is sprayed equally over the mass, the whole being intimately mixed with long stirring poles. The water is renewed twice during a period of 12 days, the time allowed for the skins to soak. They are now removed to a chamber, in which a moderate increase of heat facilitates the saponification of the fat and the dissolving of the fleshy matter. The chamber is a brick building, with a cemented floor, on which the skins are spread to a uniform depth of about six inches and is heated by steam pipes running round the building. At a temperature of about 70° F. the skins are exposed two or three days, with frequent turning. They are now transferred to the washing machine and washed until the effluent is practically free of soda or lime. The skins then undergo a bleaching process to whiten, and thus destroy any injurious coloring matter. For this purpose the washed skins are removed to a number of vats fitted with folding covers, and treated to a solution of sulphurous acid of ½° Twaddell strength for 24 hours, each vat being well stirred at intervals to allow the “bleach” to permeate equally the mass.

In some factories this process is carried out with dry sulphurous acid, the gas being generated in a sulphur burner and, after washing, passed into a chamber containing the skins. The vats are now drained, then filled up with water, well stirred, and the water run off. This is repeated until the effluent is practically free of any sulphurous smell, and the work of dissolving the gelatine is proceeded with. The digesting of the skins is carried on in stoutly built, circular wooden vats, each having a size, generally of 4 feet 6 inches diameter and 6 feet deep, and fitted with 2¼ inch copper steam coil. The vats are provided with a double wooden bottom to divide the heat. They are arranged on the first floor of the building, the liquors running through a shallow filter of fine copper gauze to the clarifying vats beneath. The skins are raised by an elevator and fed direct into the vats by suitably-arranged troughs, then covered with water, and steam is sent through the coils. The temperature is frequently taken by the thermometer and should never exceed 177° F. During the digestion, any unsaponified fat and dirt comes to the surface as a scum, and is carefully skimmed off from time to time. Samples are also drawn of the liquors, cooled, and the appearance and strength of the jelly noted. After five to six hours’ heating, the first liquors are run off to the clarifying vats, at a strength of about 17 per cent. gelatine.

The vats are refilled with water, and a second digestion made, the liquor running to the clarifying vats at a strength of 12 per cent. In the third digestion the temperature is raised a few degrees to practically exhaust the gelatinous matter, and can either be clarified to form an inferior gelatine, or concentrated for size. The exhausted matter is taken to the manure-shed for mixing purposes. The clarifying of the first and second liquors—and if used for gelatine the third liquor—is done separately in the clarifying vats. The clearing agent used is alum, to the extent of ½ per cent., or a little blood diluted with water; both are mixed with a small portion of the hot liquors in a bucket, and then well stirred in the vats. The liquors are raised to 177° F. to coagulate the impurities, and then lowered to 149° F. and allowed to stand for two hours. During this time the coagulated matter rises to the surface, and is skimmed off. On leaving the vats, the liquors are filtered through fine copper gauze into a receiver from which is fed the vacuum pan.

Gelatinous liquors being peculiarly sensitive, especially as regards color, to high temperatures, it is found advisable to evaporate them in vacuo; and this method is adopted by all continental makers. The three grades of the liquors, concentrated to the required strength, are run on to squares of glass, 4´ × 4´, fixed in a wood framing, to a depth of ½ inch for cake and ¼ inch for leaf gelatine, then placed perfectly level on racks for jellying. In 24 hours the jelly is firm, and can be easily cut to the desired size of cake or leaf wanted. A very fine gelatine is produced by cutting the jelly into small pieces, washing well with cold water, and remelting at a temperature of 176° F., and poured again on the glasses for jellying.

The drying is carried on by exposing the cut cakes, on nets fixed to a framework of wood, to a rapid current of dry air in the tunnels, as described in the drying of glue.

BONE GELATINE.

The materials used for this purpose should be of the best description, the most suitable bones being calves’ feet, waste of turners and button makers, the bony cores of the horns of the ox and cow. Such bones do not require comminution, but if large bones of oxen, horses, etc., are to be used, it is recommended to break them as small as possible by means of a wooden mallet, and to avoid the use of iron stampers, as the bones become heated by the heavy blows and friction to which they are subjected during the process, and acquire an empyreumatic odor which is retained by the gelatine.

The next step in the process is the solution of the glue cartilage. This was formerly effected by the use of steam and water. The crushed bones were placed in a wire basket or cage and this inserted in a small cast-iron cylinder and steam introduced. The apparatus is connected with a steam boiler, and provided with an air-tight lid, and a pipe and a rose connected with a water reservoir for pouring water over the bones in order to promote the solution of the glue cartilage. But this process is very slow, 20 hours being required without completely exhausting the bones.

The resulting gelatinous liquor is drawn off every hour, the first run, which contains the dirt and grease, being, of course, kept separate from the rest.

As will be readily understood this process consumes much fuel, and leaves a residue which, though not completely exhausted, cannot be further utilized for the preparation of gelatine. In fact the entire process is obsolete, but as it is still in use in some localities, a description is here given, for the sake of completeness, of the apparatus and improved manner of manufacture employed in the factory of D. J. Briers, which is well known for the beautiful product turned out.

Fig. 59 shows a longitudinal section of the entire apparatus.

Fig. 60 is the horizontal section of the boiler.

_a_, is the cylindrical boiler 6 meters (19.68 feet) long, and 2 meters (6.56 feet) in diameter. It is made of strong boiler plate doubly riveted, and capable of resisting a pressure of six or seven atmospheres.

_b_, is the manhole. It is closed by an oval lid secured by two iron rods and two bolts, so that after placing the lid in position, the boiler is hermetically closed by tightening the nuts upon the bolts.

_c_, is a cast-iron fork with two safety valves with levers graduated from 1 to 100 atmospheric degrees.

_d_, is a float upon the surface of the water, and provided with a wheel graduated from Nos. 1 to 6. Its object is to indicate during the operation how much water is lost and how much remains in the boiler. Care must be had not to allow the indicator of the wheel to get below No. 1. This figure indicates that the water has reached the highest point in the boiler exposed to the fire, which is consequently the lowest point which the water can be allowed to reach. On the other hand the indicator must not move above No. 6, as the water when standing too high in the boiler and too close to the pipes conducting the steam into the various apparatuses might mix with the steam and spoil the operation carried on in the drum, _e_, Fig. 60.

_f_, Fig 60, is a manometer, which indicates the degrees of pressure exerted by the steam in the interior of the boiler. It consists of a wrought-iron pipe bent double, and is filled with mercury 1.22 meter (4.002 feet) high counted from its base. One end of the pipe communicates with the boiler, while the other end is provided with a small brass wheel. Upon the latter is a thread of twisted silk, to the end of which is suspended an iron cylinder of somewhat smaller circumference than the bore of the pipe, so that it can move up and down in it without friction. This cylinder rests always upon the mercury. To the other end of the thread is fastened an indicator of somewhat less weight than the cylinder, which, by sliding in a groove in a graduated board placed alongside the pipe, indicates the degrees of steam pressure.

_g_ is a cast-iron pipe for heating the drying room, and

_h_ another cast-iron pipe for heating the store-room for the bones.

_i_ is the forcing pump for feeding the boiler with water.

_k_ is a sheet-iron reservoir placed close to the end of the boiler. It is filled with water, which is heated by the heat lost in the fire-place in consequence of the draught, and by allowing the smoke to circulate under the reservoir before passing into the chimney. The reservoir communicates with the forcing-pump by means of a pipe and stopcock, so as to avoid feeding the boiler with cold water.

_l_ is the fire-place, consisting of the grate, door and cast-iron frame.

The drum, _e_, is a spherical vessel of strong sheet-iron doubly riveted. It is 3 meters (9.84 feet) in diameter, and capable of resisting a pressure of six to seven atmospheres. It serves for softening the bones with the assistance of steam passed into it from the boiler, _a_. It is provided with a manhole similar to that of the boiler.

_n_ is a wrought-iron shaft passing horizontally through the drum and revolving in the brasses, _o_.

_g_, Fig. 61, is a gearing with a crank, by means of which the drum _e_ is revolved. The power of the gearing must be so calculated that one man can turn the wheels when the drum is filled with water.

_r_ is a false bottom perforated in its entire length with holes 12 millimeters (0.47 inch) in diameter, and is placed about 15 centimeters (5.9 inches) above the true bottom of the drum. It consists of two pieces, and is secured by two nuts, so that it can be easily removed and replaced. Its object is to prevent the bones from clogging up the pipe _s_, and the cocks _t_, _u_.

_a_, _a_, Fig. 61, are angular iron points inside of the drum _e_. Their object is to facilitate the shifting of the bones when the drum is revolving.

_x_, Fig. 59, is a cock near the manhole. It is opened about 2 millimeters (0.079 inch) during the operation in the drum. It serves also for the escape of the steam from the drum when the operation is finished.

The cocks _t_, _u_, placed in the lower part of the drum, serve for the escape of steam condensed during the operation.

The steam pipe _p_, Fig. 59, conducts the steam from the vessel _a_ into the drum _e_.

_y_, Fig. 59, is a cock graduated into eight equal parts and placed on the steam pipe _p_, to conduct the steam from the box _z_, into the stuffing box _a´_, and from there into the pipe _s_, then under the false bottom _r_, into the drum _e_.

The lid of the cast-iron box _z_, is provided with a safety valve loaded with a weight corresponding to the pressure of one atmosphere.

The wooden vessel or box _d_, the ground-plan of which is shown in Fig. 62, serves for boiling the comminuted bones in order to extract the jelly. This box consists of the following parts:—

_n_, are cast-iron steam pipes occupying the entire surface of the box, being placed at equal distances from each other, and connected on their ends by semicircular pieces. The steam, which is allowed to circulate in the pipes in order to boil the liquid, enters through one of the ends which rises up vertically and is connected with the cock _h´_, Fig. 59. The other end is secured to the inner side of the box, which is perforated for the admittance of the cock _o´_. Upon the steam pipes lies a wooden framework with linen nailed upon it, the object of which is to prevent the comminuted bone substance from falling under the pipes. The frame must, of course, fit closely into the box.

The cock _h´_ graduated in eight equal parts serves to admit steam into the pipes _n´_, and is opened either entirely or half, or one-quarter, or one-eighth, according to the stronger or gentler ebullition to be produced.

To prevent the steam from becoming stagnant in the steam pipes _n´_, a small jet is allowed constantly to escape through the cock _o´_. The latter serves also to run off the condensed steam when it no longer possesses the heat required to keep up ebullition.

_p´_, Fig. 62, is a cock in the bottom of the box _d´_ for drawing off the gelatinous solution from the residue. The box _e´_, Fig. 62, a ground-plan of which is shown in Fig. 63, serves for evaporating the gelatinous solution, which is effected by circulating steam through several tubular pieces of cast-iron which form the bottom of the box and are connected in a similar manner as the pipes in the box _d´_.

The cock _i_ is graduated and similar to _h´_.

The cock _r´_, Fig. 63, is similar to _o´_, Figs. 59 and 62.

_s´_, Fig. 63, is a cock for drawing off the evaporated gelatinous solution.

The wooden box _f´_, Fig. 59, a ground-plan of which is shown in Fig. 64, serves for the reception and settling of the evaporated gelatinous solution. Its bottom is constructed in a manner similar to that of the box _e´_.

The cock _n´_, which is placed 14 millimeters (0.55 inch) above the bottom of the box, serves for running the gelatinous solution into the wooden cooling-boxes.

The bones as received in the factory are sorted by throwing out the spongy material, etc. They are then steeped in lime-water for a few days to free them from adhering particles of flesh, after which they are dried and stored away for future use.

The boiler _a_, is filled two-thirds with water, and heated until the manometer indicates a pressure of 30°. In the meanwhile the drum _e_, is filled seven-eighths with perfectly dry bones, and steam is then admitted from the boiler _a_, through the graduated cock _y_. The fact that the bones in the drum are exposed to the proper temperature of 250° F. is recognized by the thermometer _b´_, placed between the cock and the drum.

To prevent the stagnation of the steam in the drum, _a_ small jet of it is allowed constantly during the operation to escape through the cock _x_. The cock must not be opened wider than is necessary to keep the temperature at 250° F. By opening it wider, this degree would be exceeded, and the gelatine-yielding substance would, in consequence, undergo alteration. A quarter of an hour after admitting the steam into the drum, the cock _t_, is opened, and again closed after allowing a small portion of the condensed steam to escape to the cock _u_, and, through this, into a box. This operation is repeated every quarter of an hour.

To change the position of the bones, the drum is revolved twice every half hour, by means of the gearing _q_, of course closing the cock _x_ during the operation.

By carefully following the above rules, the bones will be thoroughly reduced in four hours. If, for instance, steam has been introduced into the drum at 5 o’clock a. m. the operation will be finished at 9 a. m. The cock _y_, is then closed, and the steam allowed to escape through the cock _x_. After the escape of the steam, the drum is emptied, by removing the lid and turning it upside down. It is then refilled with entirely dry bones, and the operation continued in a like manner, day and night, if necessary.

After the bones have been taken from the drum, they are spread out under a shed, and, when dry, ground in a suitable mill. The resulting flour, which contains the jelly-yielding substance, is brought into the vessel _d´_, which, in the meanwhile, has been furnished with sufficient water to cover the flour 65 centimeters (25.59 inches) deep. The mixture is boiled for three-quarters of an hour, being constantly stirred to prevent the flour from forming a heavy and dense mass which would hinder the quick extraction of the jelly. Ebullition is then interrupted by closing the cock _h_, and the fat floating on the surface skimmed off. After allowing the gelatinous solution to settle, it is drawn off by means of a faucet placed above the level of the flour. Thirty bucketfuls of the gelatinous solution are then at once poured into a vat and mixed with the condensed steam drawn off by means of the cocks _t u_, during the reduction of the bones in the drum. After allowing the mixture to cool to 160° to 155° F., 20 kilogr. (44 lbs.) of pulverized alum are added at once and as quickly as possible. When the gelatinous solution has become transparent, it is drawn off into the box _e´_, and a few bucketfuls of hot water are poured upon the sediment in the vat in order to extract the remaining jelly, which is effected by thorough stirring and allowing to settle until the water is entirely clear.

After disposing of the 30 bucketfuls in the manner mentioned, the remainder of the gelatinous solution is evaporated. This is accomplished in the box _e´_, which is filled 8 centimeters (3.15 inches) deep with gelatinous solution, and steam is then admitted into the tubular bottom pieces. To promote evaporation and keep the fluid constantly in motion, the cock _i´_ is only opened far enough to keep up gentle ebullition. During evaporation the solution should be frequently stirred with an implement resembling a rake. The nearer the required degree of concentration is approached, the greater care must be exercised to prevent the solution from boiling too strongly. The proper degree of consistency is obtained when half a saucer full of the solution placed in a shady place in the air acquires in a short time such a consistency that when touched with the finger no impression remains. The cock _i´_ is then closed, and the jelly is drawn off into the box _d´_, which contains the 30 bucketfuls of clarified jelly, care being had to mix the two solutions as quickly as possible. After evaporating all the gelatinous solution and mixing it in the box _d´_, the whole is heated to 158° F., by admitting steam through the cock _k´_, care being had not to forget closing it as soon as the above temperature has been reached. The solution is then thoroughly stirred and permitted to settle for three hours to allow of the precipitation of the lime salts decomposed by the alum. The fluid, which is now perfectly transparent and of a beautiful dark-yellow color, is then drawn off into wooden cooling boxes 2 to 2.5 meters (6.56 to 8.2 feet) long, 20 centimeters (7.87 inches) wide, and 16 centimeters (6.30 inches) deep. The following day the gelatine is cut into leaves 25 centimeters (9.84 inches) long and 12 centimeters (4.72 inches) wide, which are dried upon nets. When quite dry, the drying process is finished by bringing the leaves into the drying-room which is heated by the pipe _g_. (Fig. 59.)

The bone flour remaining in the box _d´_ still contains much jelly, which is extracted by pressure. This is accomplished immediately after running off the gelatinous solution into the evaporating vessel. The liquid which has drained through the cloth frame previously mentioned, is drawn off by opening the cock _p´_, Fig. 62, while the residue in the box _d´_ is placed in coarse bags and the jelly extracted by subjecting the bags to strong pressure under an iron screw-press. Before mixing the extracted fluid with the solution in the evaporating vessel, it is recommended to allow it to settle, as it is always more or less turbid. The residue remaining in the bags is an excellent manure.

The modern process of preparing bone gelatine, which is now almost in general use is as follows: Clean bones are selected for the purpose, and the operation commences with the extraction of the fat by means of benzine, though some manufacturers prefer carbon disulphide as a solvent, because it is claimed that by reason of its low boiling-point it does not injure the gelatine in the same manner as benzine, and besides it leaves no smell in the degreased bones. It is advisable to bleach the degreased bones, spread out in thin layers and kept constantly moist, by exposure to the action of air and light. The bleached bones are conveyed to large vats for the purpose of extracting their mineral constituents by digestion with hydrochloric acid. If the gelatine is to be used as an article of food, or for medicinal purposes, only the purest hydrochloric acid obtainable should be used, while the ordinary article suffices for that for technical purposes.

The vats are filled three parts full with bones and the latter covered with a solution of hydrochloric acid of 10 per cent. strength. Digestion is carried on until the bones become soft, flexible and semi-transparent. The acid water is now drained off, and a supply of fresh water added, and then discharged. This is repeated until the last water is entirely free of acid, which is known by adding a few drops of silver nitrate, the absence of any white precipitate indicating that the water is entirely free of acid.

The bones are now bleached in the manner as described under skin-gelatine, preferably with solution of sulphurous acid, the process with gaseous sulphurous acid being difficult to carry out and considerable time is required for the gas to completely permeate the cartilaginous mass. The bleached bones are then conveyed to the boiling vats and the resulting liquors treated in the same manner as described under skin-gelatine.

As bone-gelatine solidifies with a larger content of water than the product from skins, evaporation of the liquors may be early interrupted and the resulting jelly cut into thin leaves which are finally dried.

COLORED GELATINE.

Cakes or leaves not entirely colorless may be utilized for colored gelatine which is employed for various purposes. Coloring is effected by simply dissolving and distributing uniformly a suitable quantity of coloring matter in the clarified gelatine liquor previous to solidifying; of course only water-soluble coloring matter should be used.

Colored gelatines are frequently used by confectioners and in the household in the preparation of jellies, and the use of poisonous colors should under all conditions be avoided. Sufficient attention is not paid to this, because many of the aniline colors which are now so much used for the purpose are at least open to suspicion, while others, especially picric acid, which yields a beautiful yellow color, are decidedly poisonous.

The following coloring matters are perfectly harmless and yield good results in coloring gelatine:

_Yellow_: Caramel or sugar color. A still more beautiful yellow is obtained by the use of an aqueous extract of saffron.

_Red_: Extract of cochineal.

_Blue_: Indigo-carmine solution.

_Green_: Mixture of indigo-carmine and caramel.

_Violet_: Mixture of extract of cochineal and indigo-carmine.

While gelatine colored with the above-mentioned coloring matter does not present such a beautiful appearance as the product colored with aniline colors, it is entirely harmless and suitable for culinary purposes.

Leaves of gelatine colored with aniline colors exhibit beautiful colors and are used for many technical purposes. The following colors may be employed:

_Yellow_: Picric acid soluble in hot water.

_Red_: Fuchsine or eosine.

_Blue_: Water-soluble blue.

_Green_: Iodine green.

_Violet_: Methyl violet.

_Gelatine for Fining Purposes._

For fining beer, wine, etc., gelatine in leaves or in powder is brought into commerce. For the preparation of leaves, gelatine particularly well dried is carefully melted over a water-bath and then ladled into sheet-metal moulds, and allowed slowly to solidify.

The product brought into commerce under the name of _Gelatine Lainée_ which commands a high price is in many cases nothing but thoroughly purified bone-glue of a dark honey-yellow to brown color.

Fining powder for wine and beer is made by grinding off-color gelatine cakes and freeing the resulting powder from coarser pieces by sifting. The powder is white.

_Liquid fining gelatine._ This preparation consists of gelatine-solution suitably prepared, and represents a colorless, or at the utmost slightly opalescent, product just sufficiently concentrated to remain liquid.

Skin-liquors can only be used for the preparation of liquid gelatine, as bone-liquors already gelatinize when they contain scarcely more than 1 per cent. of glue. The skin liquors are concentrated so far as to remain liquid at a temperature of from 60° to 68° F.

A product answering all demands is obtained as follows: A good quality of gelatine of a pale color is dissolved in a sufficient quantity of water, the solution, in case it shows a slight odor, filtered through animal charcoal, and then brought into bottles. To prevent putrefaction the liquid gelatine is sterilized as follows:

The filled bottles being placed in a boiler filled to a proper depth with water, the latter is slowly brought to boiling which is kept up for 15 to 20 minutes. The bottles are then closed with corks previously boiled in the water.

_Preparation of Gelatine from Ordinary Glue._

For this purpose ordinary pale-colored glue is allowed to swell up for two days in cold strong vinegar. The vinegar is then drained off and the glue which is now almost colorless, is placed upon a sieve and allowed to float in a vessel filled with water for 10 to 12 hours. It is then placed upon a linen cloth, stretched in a room heated to at the utmost 68° F., allowed to drain and dry to such an extent that on heating it to between 158° and 167° F., a thick clear liquid is obtained. This liquid is carefully poured upon plates of glass or marble, so as to avoid the formation of air bubbles and when solidified the leaves are removed and completely dried in the air. The product thus obtained being entirely tasteless and almost colorless may be used in the preparation of jellies, as well as for foils for pictures, etc.

_Preparation of Gelatine for Photographic Printing and for Photographic Purposes in General._

Gelatine suitable for this purpose should be colorless and free from all salts, since the latter would exert a disturbing effect upon the chemical processes which take place during the photographic operation. For the removal of the salts the gelatine is treated as follows: Colorless gelatine of the best quality is broken into small pieces and covered with 10 to 12 times the quantity of water, the latter being changed every 15 to 20 minutes until the last water shows no trace of lime, which is known by adding to the water solution of oxalate; the absence of turbidity indicates that the water is free from lime. The white of an egg is now mixed with five drops of ammonia and twice the volume of distilled water and shaken to froth in a bottle. This quantity suffices for 6 to 8 ozs. of gelatine. The washed gelatine is next melted in a dish and mixed with the white of egg. One part of glacial acetic acid mixed with 250 parts of water is then added drop by drop, stirring constantly until sensitive litmus paper shows an acid reaction. The liquid is now rapidly brought to the boiling-point, whilst stirring constantly, and then filtered in a warm place to avoid gelatinization. The gelatine now contains only the salts of the white of egg, some ammonium acetate and free acetic acid. For their removal the solidified gelatine is cut into pieces, which are placed in water.

_Gelatine Capsules for Medicinal Purposes._

Considerable use is made of gelatine in medicine. To disguise the disagreeable taste of some medicines they are either mixed with gelatine solution or inclosed in gelatine capsules. To prepare the latter, dissolve 8 parts of gelatine, 2 of sugar, and 1 of gum-arabic in 8 of water in a water-bath, and dip the pear-shaped ends of iron rods into the lukewarm solution. To facilitate the detaching of the gelatine film from the rods, grease the pear-shaped ends with oil. The capsules are dried by placing them in holes of a corresponding size in boards. When dry they are filled with the respective medicine, and closed with a drop of the same solution.

_Court Plaster._

Gelatine or isinglass 155 grains, alcohol 13½ fluid drachms, glycerine 15½ grains. Water, tincture of benzoin, each a sufficient quantity. Dissolve the gelatine in a sufficient quantity of hot water to make the solution weigh 4½ ozs. Spread one-half of this in successive layers by means of a brush upon taffeta stretched upon a frame so as to present a level surface, waiting after each application until the layer is dry. For the first two applications the gelatine solution should be warmed merely to above its congealing point, so that when spread out it may rapidly solidify and at the same time adhere to, but not pass through the fabric. Mix the second half of the gelatine solution with the alcohol and glycerine, and apply it in the same manner. Then reverse the taffeta, coat it on the back with the tincture of benzoin and allow it to become perfectly dry. The tincture of benzoin applied to the reverse side leaves a thin layer of resin which in a measure renders the plaster water-proof; it is, however, advisable to repeat this application once or twice. The addition of glycerine to the last portion of the gelatine solution prevents the plaster from breaking, and preserves its flexibility for a long time. When the plaster is dry it is cut in pieces of suitable length and preserved in well-closed vessels.

_Gelatine Foils._

Large quantities of gelatine foils, which are leaves of gelatine about as thick as a sheet of paper, are produced in England and France where their manufacture forms a special branch of industry. They are either simply colored or printed with neat designs in gold or silver.

The fabrication is quite simple. Cover pure gelatine with water, and after swelling up, pour off the water and dissolve the jelly over a water-bath. After allowing the solution to cool somewhat, add the coloring matter previously dissolved in water.

In place of pure gelatine, a solution of ordinary bone-glue may be used. In order to clarify it add O.14 oz. of oxalic acid dissolved in water to every 5.5 lbs. of glue. To make the foils more flexible add also one-half pint of spirit of wine and O.28 oz. of rock candy or a small quantity of glycerine.

Aniline colors soluble in water are best adapted for coloring the foils; for _red_, fuchsine, eosine or ponceau, for _blue_, _blue de Parme_, for _green_, aldehyde green, for _yellow_, picric acid, and for the various shades, mixtures of the above colors.

A durable blue is also produced by indigo solution, yellow, by decoction of saffron, green, by mixing blue and yellow, red, by a solution of carmine in spirit of sal ammoniac, and violet, by mixing blue and carmine.

The gelatine solutions are poured upon ground-glass plates, previously polished with elutriated rouge, and rubbed with Spanish chalk. The foils are so smooth upon the glass side that when dry they can be detached without much difficulty. If both sides are required to be smooth, the foils are dried between two glass plates. In many respects their manufacture resembles that of “Gelatine Veneers.”

Gelatine foils are used for printing sacred images, visiting cards, labels, in the manufacture of fancy articles, artificial flowers, etc.

For the manufacture of artificial flowers very soft and flexible sheets are made by adding ½ part of glycerine to 1 part of gelatine and mixing intimately in dissolving the gelatine.

Such gelatine sheets brushed over in addition with Peruvian balsam can also be advantageously used for tying up wounds instead of gutta-percha cloth which tears easily and rots soon. They form an air-tight bandage which clings closely to the parts of the body, and beside the glycerine contained in them exerts a beneficial cooling effect and acts as an antiseptic.

_Gelatine Veneers._

Franchi, as far back as 1814, prepared artificial ivory by mixing gelatine solution with earthy substances. This idea has been again taken up in modern times for the manufacture of veneers imitating not only ivory, but also avanturin, lapis lazuli, malachite, mother-of-pearl, and tortoise shell. These imitations are much liked by manufacturers of fancy articles, workers in leather, cabinet-makers, etc. They are prepared as follows:—

The process may be divided into five principal operations: 1. Preparation of the glass and marble plates; 2. Preparation of the glue solutions; 3. Pouring the colored solutions upon the plates; 4. Transferring the layer of glue to the layer of gelatine; and 5. Drying the veneers and detaching them from the plates.

1. _Preparation of the plates._ Both marble and glass plates are used for imitations of marble, but glass plates only for imitations of mother-of-pearl. The glass plates must be ground, but need not exceed O.11 to O.15 in. in thickness, and only require careful washing and drying for imitations of mother-of-pearl. For imitations of marble they should be rubbed with an oiled linen rag. Other glass plates, after being washed and polished with elutriated rouge and water, are wiped with a soft rag to remove any particle of the polishing powder. The polished surface is then gently rubbed with a rag dipped in pure Spanish chalk, and the excess of chalk carefully dusted off.

2. _Preparation of the glue solutions._ For one dozen plates, each 10¾ square feet, soak 2 lbs. of good, colorless glue in water for 24 hours, pour off the water and melt the glue in a water-bath and stir in 3½ ozs. of glycerine. For imitating marbles of two colors, compound 20 to 24 fluidounces of this glue solution with the quantities of thoroughly ground mineral colors given below; the rest of the glue solution is mixed with 6.34 ozs. of zinc white ground very fine. For imitating marble of three colors mix 14 fluidounces of the glue solution with one of the coloring matters and 14 fluidounces with the other coloring matter, and the remainder with zinc white. For imitating marble with four colors, take 10 fluidounces of the glue solution to each of the three coloring matters, and mix the rest with 4½ ozs. of zinc white.

The proportions by weight of the mixtures for 10 different varieties of imitations of marble and enamel are as follows:—

_a._ Mix 20 fluidounces of the glue solution with 1¾ ozs. of rouge and 2½ ozs. of zinc white, and the rest of the glue solution with 6⅓ ozs. of zinc white.

_b._ Mix 20 fluidounces of the glue solution with 1¾ ozs. of rouge, and the rest of the glue solution with 5¼ ozs. of zinc white.

_c._ Mix 14 fluidounces of the glue solution with 1¼ ozs. of zinc white and 1 oz. of rouge, 14 fluidounces of the glue solution with 1 oz. of yellow ochre, and the rest with 5¼ ozs. of zinc white.

_d._ Mix 14 fluidounces of the glue solution with 1 oz. of rouge, 14 fluidounces of the glue solution with ¾ oz. of sepia, and the rest with 5¼ ozs. of zinc white.

_e._ Compound 20⅓ fluidounces of the glue solution with 1 oz. of quite concentrated and filtered solution of aniline black, and the rest with 6⅓ ozs. of zinc white.

_f._ Mix 10 ozs. of the glue solution with 0.8 oz. of rouge, 10 fluidounces of the glue solution with 0.8 oz. of yellow ochre, 10 fluidounces of the glue solution with 0.8 oz. of sepia, and the rest with 4¼ ozs. of zinc white.

_g._ Mix 20.3 fluidounces of the glue solution with 1.41 ozs. of lampblack. For gray add sufficient zinc white to produce the desired shade. The rest of the glue solution is mixed with 6⅓ ozs. of zinc white.

_h._ Mix 10 fluidounces of the glue solution with 0.8 oz. of umber, 10 fluidounces of the glue solution with 0.8 oz. of bole, 10 fluidounces of the glue solution with 0.8 oz. of ochre, and the rest with 4½ ozs. of zinc white.

_i._ _For enamels_ mix 20.3 fluidounces of the glue solution with 1 oz. of ultramarine, and the rest with 6⅓ ozs. of zinc white.

_k._ Mix 20.3 fluidounces of the glue solution with 1.41 ozs. of chrome green, and the rest with 6⅓ ozs. of zinc white.

For imitating mother-of-pearl veneers, 0.42 oz. of silver bronze, which need not be genuine, is ground with a little glue solution or water and intimately mixed with the above solution of glue. The bronze powder must not be in a dry state when stirred into the glue, as lumps would be formed and the veneers become spotted. In place of bronze, essence of fish scales, which is of course far more costly, can be used.[2] The glue solution thus prepared is then compounded with different aniline colors according to the tint desired.

[2] This preparation is also known by the name _Essence d’Orient_. The material for its production is furnished by a small white fish very common in the rivers of continental Europe. It accompanies the scales of this fish, and is detached when the scales are triturated for a considerable time and thrown into a vessel of water. To collect the essence the water is poured off upon a fine hair sieve, which retains the scales and allows the water and the product sought to pass through. The latter sinks to the bottom, and is obtained pure by decanting the water. A little ammonia is added to prevent decomposition.

_a._ For yellowish veneers no coloring matter is required, or the desired shade is obtained by an addition of some solution of picric acid.

_b._ For colorless veneers or those of slightly reddish tints a smaller or greater number of drops of a concentrated solution of fuchsine are added in order to counteract the yellowish color of the glue solution. For these imitations of mother-of-pearl veneers, concentrated solution of gelatine compound with 15 per cent. of glycerine can be employed, especially when essence of fish scales is used.

_c._ For _blue_, the glue solution is compounded with _bleu de Lyons_, care being had not to use too much, as otherwise the imitation becomes indistinct. The proper degree of coloring is tested by allowing a few drops of the colored glue solution to fall upon a glass plate.

_d._ For _red_, solution of fuchsine or carmine is used, the latter being obtained by dissolving commercial carmine powder in alcohol.

_e._ _Orange colors_ are produced by an addition of solution of _chrysaniline_ generally sold under the name of Victoria orange, and _violet_ by adding aniline violet. For these, as well as for the solution colored with fuchsine, the plates must _not_ be rubbed with oil, as even the smallest trace of the latter discolors these colors in drying, or at least the veneers will show spots without color.

3. _Pouring the colored solutions of glue upon the plates._ For imitations of marble and enamel, the glass plates, after rubbing with oil, are placed, rubbed surface up, in a perfectly level position. The proper portion of the white ground-mass, after becoming somewhat thickish, is then poured upon the plates, and the gaps left free in pouring filled in and smoothed with a knife-shaped tool of horn or bone. Upon this white ground the respective colored glue solutions are then poured in a zigzag form, and in conformity with the desired design, drawn through the ground-mass with a glass rod. If several differently colored glue solutions are to be applied, as given, for instance, under 2_f_, they should be poured in quick succession, so that the succeeding color runs into the preceding, and a white strip or spot remains between each color. The whole is then intermingled by the glass rod, according to the design. If the latter is to have sharply defined lines and spots, the respective colored solution of glue is used somewhat thicker, but if, on the other hand, the design is to be somewhat blended, the glue solutions are used somewhat warmer, and consequently more thinly fluid. After solidification of the glue solutions the plates are placed in a cool room for two or three hours.

Imitations of malachite are prepared in a similar manner. Four glue solutions of different shades of green from the darkest to the lightest tint are prepared and poured upon a slightly greenish ground, so as to imitate the characteristic curves and veins of malachite, which are then further traced with a comb with teeth standing at unequal distances from each other.

The glass plates set aside to be used for imitation of mother-of-pearl are now taken in hand. The solutions of glue are kept warm over a water bath and thoroughly stirred every time before pouring them upon the plates. The formation of a film on the surface of the glue solution must be strictly avoided.

For pouring out the solutions it is best to use a porcelain vessel provided with a spout and handle, and having a capacity of about 6¾ fluidounces. The portion of glue solution required for each plate (1¾ flu. oz.) is then measured into one of the porcelain vessels, and, after standing a short time, poured upon the plate and uniformly distributed. The production of a mother-of-pearl design requires some skill and practice. A comb with teeth set ½ inch apart is used. It is held in a somewhat oblique position, the teeth are gently pressed upon the glass plate, and, with frequent turnings of the comb at a right angle, cycloidal motions executed. The operation is carried on from the front to the back edge of the glass plate, and when the glue begins to thicken on the edges, continued at the softer places until the desired design is produced, care being had not to touch places which have already acquired a certain degree of solidity, as this would mar the pattern. After treating all the plates in this manner, they are set aside in a cool room for two or three hours.

4. _Transferring the layer of glue to a layer of gelatine._ For each dozen of veneers soak 2½ ozs. of gelatine, and then melt them in a water-bath, and after adding glycerine equal to 10 per cent. of the dry gelatine, let the mixture settle.

The glass plates treated with rouge and Spanish chalk are now placed in a perfectly level position, and after pouring 5½ fl. ozs. of gelatine solution upon each of them, the gaps left in pouring are filled in and smoothed with the glass rod. The front edge of a plate covered with a colored layer of glue is now, glue side down, placed upon the front edge of a gelatine plate, while the back edge of the former is gradually lowered until the glue plate lies firmly upon the gelatine plate.

It may here be remarked that the gelatine solution must only be allowed to cool off sufficiently to prevent the melting of the glue plate on touching it. If it is cooler the veneers will have blisters. It must further be looked to that, before placing the first plate upon the gelatine plate, no gelatine escapes, and that any excess only runs off after the back edge of the glue plate touches that of the gelatine plate.

The plates are now allowed to rest quietly until the gelatine is congealed, when they are removed to a cool place where they remain five or six hours.

Imitations of mother-of-pearl are treated in the same manner with the exception that the gelatine solution is colored with the same coloring matter as the glue solution. For colorless or yellowish veneers the gelatine solution is not colored.

After six hours the first glass plate is detached from the layer of glue by loosening the latter around the edges with a knife blade, and the plate gradually lifted off commencing at one corner. With some care and skill, this operation is readily accomplished without detaching the gelatine mass.

5. _Drying and detaching the veneers._ The veneers with the gelatine layer still adhering to the glass plate are now dried. This is done in a heated room in which the veneers are arranged upon frames so that they stand almost perpendicular. The hot air for heating the room enters near the ceiling while the moist air is drawn away near the floor. The temperature of the lower zone where the fresh plates are placed should not exceed 68° F. The plates are moved up higher every day until, on the third or fourth day, they have become entirely dry. Before removing the veneers from the drying-room they should be tested in regard to their dryness. They are sufficiently dry, when, on pressing the finger nail upon the glue, no impression is made.

After removal from the drying-room the plates are allowed to cool off for at least two hours before detaching the veneers. The operation begins by detaching the gelatine layer on the edges with a very thin knife blade. The operator then takes hold of one corner of the veneer and draws it gradually and carefully from the glass plate. After trimming the edges the veneers are ready for use.

If the veneers are required to resist the action of water, mix with the solution of gelatine compounded with glycerine ⅓ fl. oz. of a solution of 5 parts of chrome-alum in 100 of water to every plate, and immerse the veneers for a short time after they have been detached from the first plate, in a similar solution of chrome-alum.

Veneers prepared by these methods can be used for various purposes in architecture and in the manufacture of furniture. Tennessee and other marbles have been so closely imitated, that when used for table plates, etc., the fact of their being imitations could only be detected by the closest scrutiny. The veneers are also much used for fancy and inlaid work, for coating columns, etc. To prevent their blistering and coming off, it is recommended to add one-quarter of its weight of glycerine to the glue with which they are to be attached to the articles.

_Formo-Gelatine._

This product is used as a dressing in surgery, and, according to Samuel Rideal, is obtained as follows: Gelatine in aqueous solution is precipitated by formaldehyde H.COH, or CH_{2}O, as a substance which on drying is a white powder, neutral, inodorous, and insoluble in water and dilute chemical agents. In commerce formaldehyde is met with in aqueous solution as “formalin” containing 40 per cent. of formaldehyde. If 1 Cc. of formalin be added to 200 Cc. of a 5 per cent. gelatine solution, the latter is changed into a gelatinous mass, not melted by heat nor reduced by water. If a smaller quantity of the formalin is added (1 in 1000; the jelly is said to be meltable, but with a higher tenacity) when dried it becomes insoluble in warm water. Formalin in less proportion, though it does not prevent the dried gelatine from dissolving in warm water, is said to improve the “body” of the jelly and its keeping qualities, and also the tenacity of the glue. The results of investigation show that with up to 1 per cent. of formalin the solidity of the jelly increases; above that it declines. Up to 0.02 per cent. (1 in 5,000) it redissolves in water after drying. Even with this small proportion the firmness of the jelly is sensibly increased. The English patent, 4,696, 1894, claims the addition of formalin during the manufacture of size and glue in such proportion that the product shall liquefy in warm water.

In examining commercial sheet gelatines for printers’ and photographic use, they were often found to contain small quantities of formalin. It seems to improve the quality, a very small percentage increasing the tenacity, flexibility and keeping qualities, while not affecting the transparency or rendering the material acid. When applied to articles that may be used as food, a strength of 1 in 50,000 in the final prepared product is not injurious to health, but should not be exceeded. (Rideal and Foulerton, _Public Health_, May, 1899, p. 568.)

Zimmermann applies dilute formaldehyde mixed with glycerine, vaseline, oil or yolks of eggs, with or without flour, to the surface of photographic films which are claimed to be thereby rendered more pliable and not so hard as when the formalin is applied by itself.

It will be seen that formaldehyde in more than traces renders gelatine insoluble; the product, moreover, is almost unaffected by water, is more or less hard and elastic and, owing to the antiseptic properties of the formaldehyde is nearly imperishable.

_Use of Gelatine in Bacteriology._

Gelatine fit for this purpose must be clear and bright, fairly neutral and of high gelatinizing power. For bacteriological purposes a 10 to 20 per cent. solution of gelatine in sheets or strips is made with meat broth, and this nutrient jelly, which is obtained by clarification with albumen perfectly clear and bright, forms a most useful medium for the cultivation of micro-organisms.

_Artificial Silk from Gelatine._

For the production of textile threads, Millar utilizes the property of gelatine solution mixed with potassium dichromate, becoming insoluble on exposure to light. For this purpose a clear solution of gelatine is mixed with solution of potassium dichromate in the proportion of 100 parts of gelatine to 2 or 2½ parts of potassium dichromate. The fluid should be of such a consistency as to allow of its being drawn out into fine threads which on exposure to light become insoluble. Silk woven from such threads is equal in appearance to the genuine article but of course is not so strong. It is affected by moisture, becoming limp, but regains its normal strength when dry.[3]

[3] For further information on this interesting subject, the reader is referred to “Cellulose and Cellulose Products.” By Dr. Joseph Bersch. Henry Carey Baird & Co., Philadelphia, 1904.