A preferable method of extracting starch from wheat-flour has lately been introduced by Mr. Martin. It consists in kneading the flour into dough with water, and then washing on a sieve in a stream of water. The starch is thus washed out, and nearly all the gluten remains behind as a sticky mass. Slight fermentation is induced in the wash ings, whereby the remaining portions of gluten are destroyed, and the starch is then dried. The gum-like gluten educed in this process is dried, ground, and sold as semolina, or is mixed with flour and made into maccaroni and similar pastes.
Potato Starch, now largely manufactured on the Continent, is readily obtained from the washed and rasped or grated potatoes by simple kneading of the pulp in a stream of water on an inclined plate or fine sieve ; the starch is carried off by the water, is allowed to subside, and after one or two washings by decantation, is drained in boxes lined with felt, and dried on floors of plaster of Paris. Potato starch does not, in drying, assume the columnar form characteristic of wheat starch.
Rice Starch.—For the preparation of this variety the rice is macerated for twenty-four hours iu a very weak alkaline solution, composed of nearly half an ounce of caustic soda to a gallon of water ; it is then washed, drained, reduced to a pulp, and again macerated iu a fresh quantity of soda-ley; after brisk agitation and a short repose the liquor, still containing the starch in suspension, is poured off from the vegetable fibre, which first deposits, and the starch, secumulated by subsidence, is finally dried iu the usual manner. The object of this process is the solution of the gluten in the weak alkali. If the latter be carefully neutralised by sulphuric acid the gluten is deposited in 3D flocks, and after washing may be used in the preparation of certain varieties of food, as before mentioned.
OtAer Materials for Stareh.—Mr. Simmonds states that at Oswego, in New York State, starch is made on a vast scale from maize or Indian corn. There is one factory which corers nearly three acres, and which consumes 200,000 bushels of maize yearly, whence is obtained 4,000,000 lba. of starch. Mr. Anderson, by a patent obtained in 1857, proposes ao to treat maize as to obtain starch from one portion, and oil from a residue hitherto wasted. Frequent search is made for now materials whence starch may be obtained. So far back as 1796, the Society of Arta offered a prize medal for any novelties in this direction. The
prize was awarded to Mrs. Gibbs of Portland, who obtained starch from the roots of the Arum ottreidetem-4 lb. from I peck. It was very pure, and was sold under the name of "Portland arrow-root." There is not much now made, because the rotation of crops prevents the wild arum from growing. In 1853, M. Bassot obtained a prize in France, for making starch from the Pistillariaimperialia, or crows imperial; ho washes and rasps the bulbs, and obtains starch from them in the usual way. The plant grows well in France. M. Basset estimates that 5000 lbs. a starch may come from an acre of land, and need not cost more than 4s. per est —much cheaper than potato starch. In 1857, there was a great demand for horse-chestnuta in Franc_ ,e consequence of the establishment of a factory at Nanterre for making starch from that source. Chestnut trees are very abundant In France, and the starch obtained from the fruit is said to be good.
The use of starch in the cotton manufacturing districts is very large. One print-work in Manchester consumed 8000 cwts. in 1859. .d called Glenfield starch Is, by a peculiar process, made semi transparent, for use in stiffening net and lace.
Properties of Starch.—Starch, when pure, is nearly devoid of odour and taste, and is possessed of demulcent properties when boiled In water, with which it forms a hydrate of a jelly-like character. Its Insipidity, however, hinders it from being very digestible in this state, or even when kneaded with cold water, and exposed to heat, to form biscuits. Its digestibility is greatly increased by fermentation, and hence bread or rusks are much more suitable to invalids than any unfermented preparations of flour. The best bread is formed by flour which contains the greatest proportion of gluten. The relative pro portions of starch and gluten differ not only in the different cereal grains, 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 proportion in Carolina rice than in any other grain. Potatoes yield the purest starch. It is procured from them with great ease, by simply rasping down the potatoes over a sieve, and passing a current of water over the raspings. The water passes through the sieve milky with the starch. By rest the starch subsides; it is then two or three times washed with pure water, and afterwards allowed to dry.