GELATINE, or GELATIN (Latin, gelatus, °frozen,* so named from the tendency which the substance has to congeal and become to a certain extent solid), in chem istry a substance also known as animal gluon, obtained by treating bones with dilute hydro chloric acid, which dissolves the mineral con stitucnts of the bone, consisting of phosphates and carbonates of calcium, magnesium, etc., and leaves the bone cartilage. This, when boiled for a long time with water, dissolves, and forms gelatine, which can be purified by dissolving in hot water and precipitating by alcohol. A pure variety known as isinglass is obtained from the swimming bladder of the sturgeon and other fishes. Impure gelatine glue is prepared by boiling down pieces of hide, horn, hoof, cartilage, etc., with water under pressure. Pure gelatine is amorphous, transparent in thin plates, of a yellowish-white color; it has neither taste nor smell, and is neutral to vegetable colors ; it is insoluble in alcohol and in ether. In contact with cold water it swells up, and is soluble in hot water. It is not precipitated by adds, except by tannic acid, which gives a flaky precipitate insoluble in water, alcohol and ether. The aqueous solution of gelatine
turns the plane of polarization to the left. Gelatine subjected to dry distillation yields methylamine, cyanide of ammonium, pyrrhol, etc.; by oxidation with sulphuric acid and manganese dioxide, or with chromic acid mix ture, it yields hydrocyanic acid, acids of the fatty series, benzoic aldehyde and benzoic acid, leucine and glycocol, but unlike most other proteids, no tyrosine. Gelatine boiled with caustic potash yields glycocine and leucine. Gelatine contains about 50 per cent of carbon, 6.6 of hydrogen, 18.4 of nitrogen, 25.1 of oxygen and a small amount of sulphur. Moist gela tine exposed to the air rapidly putrefies, the liquid becoming first acid, but afterward it gives off ammonia. Gelatine gives no precipitate with lead acetate, alum or ferrocyanide of po tassium. A mixture of gelatine with potassium dichromate becomes, when exposed to the ac tion of light, insoluble in water. The nutritious value of gelatine has been much overestimated. Gelatine is also made use of in photography (q.v.).