This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
Gelatin is an albuminoid substance obtained by boiling skins, cartilages, etc, with water, straining, skimming, and otherwise purifying the solution, evaporating and finally drying by exposure to the air. During the boiling the collagen contained in the cartilages, etc, is converted into gelatin, which then passes into solution.
Gelatin occurs in thin sheets, or in shreds or powder, which may be nearly colourless or pale yellow and almost free from odour and taste. In cold water it swells and when heated dissolves; it is soluble also in acetic acid and glycerin, but not in alcohol, ether, etc. A two per cent. hot aqueous solution should gelatinise on cooling, but this property is destroyed by the prolonged action of heat. Boiling with diluted hydrochloric acid converts it into the hydrochloride of glutin-peptone. An aqueous solution is precipitated by solution of tannic acid but not by dilute solutions of alum, lead acetate, or ferric chloride. It is rendered insoluble when the aqueous solution is mixed with potassium bichromate and exposed to light; formic aldehyde produces a similar change.
Gelatin is composed chiefly of the nitrogenous substance glutin. It should not yield more than two per cent. of ash.
Apart from its various technical uses, gelatin has been employed as a nutrient and as a styptic, but its value for these purposes has been over-rated. It is also used as a demulcent, and combined with glycerin as a basis for suppositories.
Isinglass (Ichthyocolla) is the dried prepared swimming bladder of the sturgeon, Acipenser Huso, Linne (N.O. Sturiones), and other species of Acipenser living in the Black Sea and Caspian Sea and the rivers which flow into them. The bladders are cut open, washed, soaked in water, spread out on a board and deprived of the outer, silvery membrane. Dried in sheets they form leaf isinglass, or several folded together, book isinglass, or rolled and folded, staple isinglass. It is prepared for use by cutting it into thin shreds.
Isinglass is whitish or pale yellow, semi-transparent, tasteless, but with a more or less perceptible odour. In cold water it softens and swells; with boiling water it forms a solution which (1 in 50), gelatinises on cooling. It consists chiefly of collagen, about 80 per cent., together with water, about 15 to 20 per cent. .