GELATINE (proper) is prepared for commercial purposes from a variety of animal substances, but chiefly from the softer parts of the hidesof oxen and calveS and the skills of sheep, such as the thin portion which covers the belly, the ears, etc.; also from bones and other parts of animals.
One of the best, if not the best of the varieties of gelatine manufactured in Great Britain, is that made by Messrs. Cox of Gorgie, near Edinburgh, which is remarkable for its great purity and strength, or gelatinizing power; they call it " sparkling" gela tine from its beautiful bright transparency, and its purification is effected by certain processes which they have patented. The materials they, use are carefully selected por tions of ox and calf hides. Another preparation, made by Mackay of Edinburgh 'pharmaceutical chemist), is deserving of special mention, as it is, prepared with, the greatest care from calves'-feet, and is especially adapted for invalids. It is. made on a limited scale, and only for a•few leading chemists.
The general method adopted with skin-parings or hide-clippings, is first to wash the pieces very carefully; they are then cut into small pieces and placed in a weak solution of caustic soda for a week or ten days, the solution being kept moderately.warm by means of steam-pipes. When this process of digestion carried on, the pieces of skin are then removed into an air-tight chamber lined with cement, and here they are kept for a time, determined according to the skill of the manufacturer and the kind of material employed, at as temperature of 70° F. They are next trans ferred to revolving cylinders supplied with an abundance of clean cold water, and after wards are placed still wet in another chamber lined wood, in which they are bleached and purified by exposure to. the fumes of burning sulphur; they next receive their final washing with cold water, which 'removes the sulpharotts 'acrid. The next operation is to squeeze them as dry as possible, and transfer them to the gelatinizing pots. which are large earthen vessels, inclosed in wooden cases, made stemmtight. Water is poured in with the pieces, and kept at a high temperature by means of the steam in the cases surrounding the pots.
By this means the gelatine is quite dissolved out of the skin, and is strained off whilst still hot: it is poured out in thin layers, which as soon as they are sufficiently cooled and consolidated, are cut into small plates, usually oblong, and laid on nets, stretched horizontally, to dry. The cross-markings observable on the plates of gelatine, in the are the marks left by the meshes of the nets.
Another process, introduced by Mr. Swineburne, consists in treating pieces of calf skin by water alone, without the soda and sulphur processes; the pieces, after simple washing, being transferred at once to the pots to be acted upon by the steam; undoubt edly, this is the purest, but the expense of preparing it prevents its general use. Inferibr gelatine is made from bones and other parts of animals, and it was stated by an eminent authority, that in Paris the enormous number of rats which are occasionally killed in the sewers and abattoirs, after being deprived of their skins, which are reserved for other purposes, are all used by the gelatine-makers. These materials are placed in cages
of wire, which are placed in steam-tight boxes, where they are submitted ter the direct action of steam of 223' F., but at a low pressure; and cold water, supplied by another pipe through the upper part of the box, is allowed to flow slowly and percolate t hrouth the contents of the cage, the water and condensed steam descend to the bottom charged with gelatine, and arc drawn off by a stop cock placed there for the purpose.
The French manufacturers succeed better than any others in clarifying these inferior gelatines, and they rarely make any others; they run their plates out very thin, which gives them greater transparency and apparent freedom from color; and they color them with most brilliant colors, and form very fine-rolled sheets, tempting the eye with an appearance of great delicacy and purity, which would at once disappear if the material were made up into the thicker plates of the British manufacturers.
The purity of gelatine may be very easily tested; thus: pour upon dry gelatine small quantity of boiling water, if pure it will form a thickish gluey colorless solution, free from smell; but if made of impure materials, it will give otf a very offensive odor, and have .a yellow gluey consistency. No article manufactured requires such careful selection of material and such nice and cleanly manipulation to insure a good marketable character; and those anxious for purity should avoid all artificially colored varieties, however temptingly got up, unless they are required for merely decorative purposes and not for food. For the value of gelatine as food, see DIET.
Isixona.ss (supposed to be derived from the German ITausenbla8e, bladder of the sturgeon), the ichthyocolla (01thus, a fish; kolla, glue) of the classical and scientific writers, was formerly obtained only from the common sturgeon (itecipenser 'sturio), and consisted of the dried air-bladder of the animal. The necessities of modern commerce. have, however, led to the discovery, that the same part in many other fishes forms good isinglass; and instead of Russia, as formerly, being almost the only producing country, we have now large quantities from South America, chiefly imported from Maranham, some from the East Indies, the Hudson's Bay Territory, New York, and, owing to prof. Owen calling the attention of the Canadian commissioners of the exhibition of 1851 to the subject, it is now brought in considerable quantities and of excellent qhality from Canada, where it is likely to prove a source of profitable industry.
The commercial varieties of this material are numerous, rind a thorough knowledge of them can only be obtained by considerable personabacquaintance with them; there fore, their names only are given, with those of the producing animals: