GELATIN (from Neo-Lat. gelatins, from Lat. gelatus, p.p. of gelare, to freeze, from gelu, frost), or GLUTIN (not gluten). A hard, yellowish, transparent, elastic substance obtained from con nective animal tissues, especially the organic constituents of bones. If bones are treated with cold dilute acids, their mineral matter is dis solved out, the residual organic matter, called ossein, retaining the shape of the bones and gradually swelling up to a transparent elastic mass. If this ossein is cautiously treated with hot dilute acids, or simply for a long time with boiling water, it is hydrolyzed and converted into gelatin. In using acids, caution is necessary in order to prevent their attacking the gelatin pro duced by them from ossein. The ordinary com mercial process for preparing gelatin consists in carefully washing the connective tissue employed (intestines, bladders, etc.), then cutting it and digesting in a dilute solution of soda lye for ten days at a moderate heat. The material is then removed into an air-tight chamber lined with cement, where it is hated at a temperature of 70° F. It is next transferred to revolving cylinders supplied with an abundance of clean cold water for washing, and afterwards is placed in another chamber, lined with wood, where it is bleached and purified by exposure to the fumes of burning sulphur, after which it is washed with cold water to remove traces of sulphurous acid. The next operation is to squeeze it as dry as possible and transfer it to the gelatinizing pots, which are large earthen vessels inclosed in steam tight wooden cases. Into these vessels water is poured, and the mass is kept at a high tempera ture by means of steam coils surrounding the pots. By this process the gelatin is dissolved out of the tissue and is strained off while still hot. It is then poured out in thin layers, which, as soon as they are sufficiently cool and consoli dated, are cut into small oblong plates and laid on nets to dry. If the solution is dark-colored it may be purified by treatment with animal or vegetable charcoal. The gelatin of bones may he extracted on a large scale by the combined action of steam and a current of water trickling over their crushed fragments in a properly constructed apparatus. When the gelatin is to be used as an article of food, the bones must be quite fresh, well preserved in brine, or dried by a stove, and should be crushed by passing between grooved iron rollers. The purification of commercial gela
tin may be effected by soaking in distilled water for some days in order to remove salts, dissolving in hot distilled water, and filtering while hot into 90 per cent, alcohol. The gelatin then sepa rates in the form of white thready masses, which can be subsequently dried. The pure gelatin thus obtained contains only about one-half per cent. of ash, and although distinctly different as a chemical substance from the proteids, it re sembles the latter in percentage composition.
Gelatin is readily digested and absorbed in the animal body, forming a food-stuff of considerable value, especially in training diets. Physiological research has shown, however, that it is in no case transformed into true proteid matter, and cannot therefore serve as material from which animal tissues are built up.
Gelatin is soluble in concentrated acetic and mineral acids; if thus treated it loses its gela tinizing property, but the solution may be used as a cement for glass and for certain other pur poses. In contact with cold water it swells up to an elastic transparent mass, which is me chanically combined with much water; the mass readily dissolves in warm water, but on cooling, the solution 'gelatinizes,' and thus gelatin is ex tensively used for culinary purposes, being em ployed as a vehicle for other materials; for in stance, in making jellies. Gelatin is further used in taking casts and impressions for electro typing, and besides being employed for gelatin dry plates in photography, it is used in the carbon processes of photographic printing, which depends on the power of certain bichromates to render the gelatin insoluble when exposed to the• action of light. This last property has also led to the use of gelatin as an insoluble glue or water proofing material. Gelatin is one of the in gredients of printers' rollers; it is also employed in dyeing, and as a size in paper-making and painting. As a fining it is employed in beer brewing, and it also finds application in medicine as a coating for pills and capsules. The crude gelatin, prepared by the simplest processes, is -called glue, and has valuable applications as a cement.
Consult: Davidowsky, Practical Treatise on the Raw Materials and Fabrication of Glue, Gela tin, etc., translated by Brannt (Philadelphia, 1884) ; Standage, Cements, Pastes, Glues, and Gums (London, 1893). See also ISINGLASS ; GLUE.