The 2 products are thus easily separated, in order to be treated in the usual way, and the hydrocarbons are recovered by evaporating with steam and condensing.
German plan for preparing gelatine from bones: - The bones are exposed to the sun and air for about 6 weeks, and in dry weather are moistened several times daily with water. Quantities of 10 to 15 cwt. are put into vats, and soaked with a solution of hydrochloric acid at 4° (? Beaume), which is drawn off when saturated^and replaced by a fresh solution, repeating till the bones are softened. These are washed in fresh water, and placed for 14 days in a solution containing a. small amount of lime, then taken out and thoroughly rewashed in fresh water, and laid out upon large plates to dry in the air. The product at this stage is raw gelatine. About 300 lb. of this is laid in running water for 24 hours, which makes it soft and easily broken up; it is then left for several days exposed to the open air, after which it is put into an immense kettle with 40 gal. river water; a fire is made, and it is slowly cooked, the mixture being stirred every 1/2 hour, and 4 oz. alum added, which helps to liberate the fatty particles, and thus materially to purify the gelatine.
After cooking for 8 to 18 hours, according to the state of the mass (which may be tested by filtering some through a linen cloth, from which it should come clear and free from all impurities), the whole is put into a vat containing 3 gal. fresh water acidulated with sulphuric acid. It is stirred, 2 qt. acetic acid are added, and the mass is left to stand for 1 hour, when it is again filtered through linen cloth, and put into wooden vessels, where it gradually attains a solid state. Before becoming thoroughly hard, it is cut by machine into thin sheets, and laid out to dry in an airy and dry spot under an awning. The very best brand of gelatine is said to be made in this way. Should it be desired to produce coloured gelatine, the following modification is needed: - On completion of the last filtration through linen cloth, a small quantity of gall is added, and then the required colouring matter. The most common colour is carmine, dissolved in aqua ammonia, and stirred into the mass. Aniline colours may also be used.
The proportions are generally 1 oz. colouring matter to 4 lb. liquid gelatine, the former being first thoroughly cleaned by repeated straining through linen cloth, then added to the diluted gelatine, and the whole well mixed while warm and poured out on large frames or sheets of glass placed in a cool, dry, airy place. The sheets are taken off when dry, or just before, if they are to be stamped with patterns.
In the method of manufacture known as Rice's, the bones are placed in dilute phosphoric acid, by which the earthy matters are dissolved and removed from the cartilage, which latter can be turned into gelatine by any ordinary process. The acid is recovered from the earthy matter for re-use in the following way: - About 2/3 or more of the solution of acid phosphate of lime is submitted to the action of sulphurous or sulphuric acid, which precipitates the lime as sulphite or sulphate, either being easily removed, and leaving the acid or acid phosphate (according to the amount of acid used) in an available condition for further use on fresh bones. By extracting the phosphates originally held in the bone, this process yields an actual surplus of phosphoric acid, so that it is claimed that almost 50 per cent, can be gained on each treatment. The residues are used for manure. The cost of production is said to be greatly reduced by this plan. Phosphoric acid alone is found to be best; but it may also be used in conjunction with other acids, in such proportions that the mixture will dissolve and remove the earthy matters.
Cox's process for making " sparkling " gelatine is as follows: - The hide and skin pieces (preferably the shoulders and cheeks of ox-hides) are washed in water, chopped fine by machinery, and reduced to pulp in a mill; this pulp is pressed between rollers, mixed with water, and submitted to a heat of 150° to 212° F. (65 1/2° to 100° C), whereby the gelatine is extracted. To obtain a very pure quality, liquid gelatine is mixed with a small quantity of ox-blood at 160° to 170° F. (71° to 77° C), and further heated; the albumen of the blood coagulates and forms a scum, which can be removed when the heat is withdrawn, leaving the purer liquor to settle, ready for running into coolers to harden and dry. The evaporation is conducted in vacuo, to reduce the temperature and duration of the operation.
Heuze obtains gelatine of good qua-lity from even inferior sources, such as the substances obtained during the manufacture of neats'-foot oil. The gelatine from this source is very dark, and hence has only a limited sale at the low rate of about 2d. per lb. By digesting for 3 hours at a pressure of 3 atmospheres, pouring off the resulting ammoniacal solution of gelatine, separating the supernatant oil, and evaporating, a black friable gelatine results. Attempts to bleach this by sulphurous acid, or a sulphite and hydrochloric acid, gave unsatisfactory results. If the digestion, however, be continued for only 1 hour, and the liquid be then run off, a second digestion for an hour following with fresh water, and after pouring off the second liquor, a third for another hour, a much better result is obtained, the liquids resulting being almost perfectly decolorized by treatment with 4 per cent, of charcoal mixture, consisting of 100 parts wood charcoal, 25 parts animal charcoal. The gelatine thus obtained can be used for food, as it has no smell, and has only a slight yellow tint when seen in large masses. (Dingier's Polytech. Jl.)
Nelson's gelatine is extracted by steam heat from hide pieces which have been submitted to the bleaching action of sulphurous acid. The strained and purified article is spread in a thin layer on a marble slab till it partially solidifies; next it is cut up and washed to free it from all traces of the acid; again dissolved at the lowest possible temperature; and finally re-solidified and dried in thin sheets on nets.