STARCH (called also Farina and Fteculam) is a proximate principle of plants, chiefly found in the seeds of corn and pulse, in many kinds of tubers, and sometimes in wood, bark, and leaves. In all these instances it is asso ciated with other principles, which are either employed with it, or separated by different processes, according to the use intended to be made of it. In wheat it is associated with variable proportions of gluten, sugar, and gum ; in potatoes chiefly with gum and sugar. It is mostly lodged in the cells of the cellular tissue, and consists of granules, always white, generally of a roundish and seldom of an angular figure. The granules differ in size, often in the same seed, being generally smallest near the circumference. They differ also in different plants. The granules are lodged mostly in the cells or compartments of the cellular tissue ; and each granule consists of a Membrane, containing a transparent colour less material resembling gum.
The insolubility of the membrane in cold water affords a means of separating the starch from the gluten in wheat-flour, and from the fibrous matter in potatoes and other tubers. Wheat-flour is formed into a paste with water, and then kneaded under a stream of water so long as the water runs off of a milky appear ance; what remains behind is chiefly gluten, while the water has carried off the starch sus pended in it; and gain, sugar, and some phosphatic salts, either dissolved or suspended in it. The water charged with these shatters is permitted to stand for a few days in summer, but for a week or two in winter, to allow the acetous fermentation to occur, by which the sugar and other principles are got rid of. The acid liquor termed sours is drawn off, and the starch thrown upon sieves, and washed ; the bran and other impurities are retained on the sieves, while the starch is carried forward into large vessels called frames. In these the
starch subsides, and the water, which has become perceptibly sour, drawn off, and the slimes removed. The starch is then washed, passed through a sieve, and finally allowed to subside. Thus purified it is put into boxes lined with canvas and perforated with holes, by which the superfluous water escapes. After wards it is cut into squares, put on bricks, and exposed to the heat of an oven, where it splits into irregular prisms. When free from any artificial admixture, it is perfectly white, and termed white Starch or French Starch : but in general, azure (smelt) or indigo is added, when it is employed for stiffening linen, to which it imparts a more agreeable hue than the dull white of that material.
Starch, when pure, is nearly devoid of odour and taste. The best bread is formed by flour which contains the greatest proportion of gluten. The relative proportions of starch and gluten differ not only fu the different cereal graihs, but in the same species or variety, according to the season when they are sown, or the manure which has been applied to the land. Starch exists in larger propor tion in Carolina rice than in any other grain. Potatoes yield the purest starch, variable in quantity with the kind of potato used, the mode of cultivation, the dm() of setting, and, above all, the time of year when the process is applied.
Starch is most extensively used in the arts, hut it is little employed in medicine, except for its demulcent properties, and as a vehicle kir opiate injections. Some of the calico printers use a kind of stiffening material or starch, which they call British gum, and which was brought into nse on account of the high price of gum senegal ; it is prepared from wheat flour, and is midway in quality between common starch and common flour-paste.