625. Gelatinum (U.S.).—Gelatin.
SOURCE.—Bone, cartilage, skin, tendons, and ligaments; a boiling-hot solution of these, resulting in a jelly when cooled, is dried in the air.
DESCRIPTION.—Thin, transparent sheets or porous, opaque layers or shreds, amorphous, swelling in water without dissolving, dissolving in warm water, forming a sticky liquid which solidifies on cooling. The solution is laevogyrate. Solutions of gelatin on boiling are not precipitated either by mineral acids, acetic acid, alum, lead acetate, or mineral salts in general, but precipitated by potassium ferrocyanide, tannic acid, mercuric chloride in the presence of HCl and NaCl, and by alcohol, especially when neutral salts are present. Its solution containing KCr2O7 yields an insoluble compound on exposure to light.
Gelatinoids.—To this group belong a number of substances occurring in bones, skins, horns, etc., having generally the property of forming a jelly with water. The organic matter in bones, usually called ossein, contains, besides albuminous substances, the two gelatinoids, collagin and gelatin, a pure mixture of which forms common glue. Chondrin resembles gelatin; it is obtained from cartilages of the ribs and non-ossifying cartilages; its aqueous solution is precipitated by alum, lead acetate, ferric salts, acetic acid, and a small quantity of mineral acid, but not precipitated by tannin or mercuric chloride. Properties: Emollient, nutritive, and protective.