The Fecula of the Seeds of Triticum Vulgare.
History. — Starch is a principle contained in various organs of many plants, as wheat, rye, barley, oats, rice, peas, beans, chestnuts, acorns, potato, etc.; and is extracted from many of them for dietetic and medicinal purposes, under the several names of Starch, Arrow-root, Tapioca, Tous-les-mois, and Sago. It abounds especially in the different kinds of grain, among which, wheat, yields one of its purest varieties, and from which an average of about from fifty to sixty per cent, is to be had. In preparing starch from wheat-flour, the flour, which consists of starch, gluten, mucilage, albumen, several salts, and some bran, is kneaded in a cloth with successive portions of cold water. The gluten and bran remain in the cloth ; the mucilage, albumen, and salts dissolve in the water ; and the starch passing away with the water in a state of suspension, gradually falls to the bottom. By allowing the albumino-mucilaginous water, from which it has subsided, to undergo fermentation, the starch is thereby purified from the gluten; for the acetic acid formed during this process, dissolves the gluten.
Starch is of the purest white, pulverulent, opake, nearly inodorous, and tasteless, and is usually had in small, columnar, irregular prisms. Its specific gravity is 1.53. In dry air it is permanent; in moist air it absorbs about twenty-four per cent, of water, without losing its dry appearance, and which may be driven off by a gentle heat. In its ordinary state it contains about twelve per cent, of moisture. It is insoluble in alcohol, ether, oils, and cold water. Alcohol removes from it a trace of essential oil, on which its odor and taste depends. Diluted sulphuric acid resolves it into sugar ; nitric acid into malic and oxalic acids. When starch has been triturated or agitated with water, a dark purple compound is formed ; a solution of starch made with hot water, and subsequently cooled, yields on the addition of iodine, an immediate deep-blue precipitate of iodide of starch ; thus iodine is the most delicate test of its presence in any mixture. The color varies with the proportions employed ; when the two substances are about equal, the compound is of a beautiful indigo-blue ; if the iodine is in excess, it is blackish-blue ; if the starch, violet-blue. A solution of iodide of starch, when heated to 200°, becomes colorless, but on cooling recovers its blue color ; boiling permanently destroys the color. Alkalies form soluble compounds with starch, from which it may be precipitated by acids. Lime-water, and baryta-water, precipitate it from its solution, forming insoluble compounds. When starch is roasted, it is converted into a substance soluble in cold water, called British Gum, which may be applied in the arts to the same purposes as gum.
Starch consists of organized granules, of various form and size, being small, globular, oval, or angular. These granules have each a thin exterior pellicle or tegument, insoluble in water, and an interior, soluble substance. Amylin is the name applied to the external tegument; amidin, to the interior mucilaginous portion. Dextrin is amidin rendered impure with variable proportions of starch-sugar, and starch-gum — and may be prepared by boiling the starch for a long time in dilute sulphuric, muriatic, or oxalic acid ; and if the boiling be still further continued, a saccharine substance is produced, similar to the sugar of grapes. Diastase is a principle developed in the seeds of barley, oats, wheat, etc., by germination. Starch consists of carbon, 44, hydrogen, 6.22, and oxygen, 49.78 ; its formula is C12 H10 O10.
Properties and Uses. — Starch is demulcent and nutritive. It is used in mucilage, or in emulsion, for suspending drugs, when to be given internally or by injection. The powder is dusted upon the skin to absorb irritating secretions; to prevent excoriation ; to soothe the pain of erysipelas, and to prevent intertrigo in infants. Starch may be used as an antidote to iodine.