jelly elly becomes brown-gray with iodine. 1. Ordinary sturch.—This may be ex tracted from the following grains ;— wheat, rye, barley, oats, buckwheat, rice; maize, millet, spelt; from the siliquose seeds, as peas, beans, lentiles, &c.; from tuberous had tap roots, as those of the po tato, the orals, manioc, arrowroot, batata, &e. Different kinds of corn yield very variable quantities of starch. Wheat differs in this respect, according to the varieties of the plant, as well as the soil, season, and climate.
Wheat partly damaged by long keep ing in granaries, may be employed for .he manufacture of starch, as this consti azent suffers less injury than the gluten; cud it may be used either in the ground or unground state.
1. With tinground wheat.—The wheat being sifted clean, is to be put into cis terns, covered with soft water, and left to steep till it becomes swollen and so soft as to be easily crushed between the fin gers. It is now to be taken out, and im mersed in clear water of a temperature equal to that of malting-barley, whence it is to be transferred into bags, which are placed in a wooden chest containing some water, and exposed to strong pressure. The water rendered milky by the starch being drawn off by is tap, fresh water is poured in, and the pressure is repeated. Instead of putting the swollen grain into bags, some prefer to grind it under ver tical edge-stones, or between a pair of horizontal rollers, and then to lay it in a cistern, and separate the starchy liquor by elutriation with successive quantities of water well stirred up with it. The re siduary matter in the sacks or cisterns contains much vegetable albumen and gluten, along with the husks ; when ex posed to fermentation, it affords a small quantity of starch ofrather inferi or quality.
The above milky liquor, obtained by expression or elutriation, is run into large cisterns, where it deposits its starch in layers successively less and less dense ; the uppermost containing a considerable proportion of gluten. The supernatant liquor being drawn off, and fresh water poured on it, the whole must be well stirred up, allowed again to settle, and the surface-liquor again withdrawn. This washing should be repeated as long as the water takes any perceptible color. As the first turbid liquor contains a mixture of gluten, sugar, gum, albumen, &c., it ferments readily, and produces a certain portion of vinegar, which helps to dis solve out the rest of the mingled gluten, and thus to bleach the starch. It is, in
fact, by the action of this fermented or soured water, and repeated washing, that 't is purified. After the last deposition and decantation, there appears on the surface of the starch a thin layer of a slimy mixture of gluten and albumen, which, being scraped off, serves for feed ing pigs or oxen; underneath will be found a starch of good quality. The lay ers of different sorts are then taken up with a wooden shovel, transferred into separate cisterns, where they are agitated with water, and passed through fine sieves. After this pap is once more well settled, the clear water is drawn off, the starchy mass is taken out, and laid on linen cloths in wicker baskets, to drain and become partially dry. When suffi ciently firm, it is out into pieces, which are spread upon other cloths, and thor oughly desiccated in a proper drying room, which in winter is heated by stoves. The upper surface of the starch is generally scraped, to remove any dusty matter, and the resulting powder is sold in that state. Wheat yields, upon an average, only from 35 to 40 per cent. of good starch. It should afford more by skilful management.
In 1839, M. Pierre Isidore Verduer ob tained a patent for making starch, the chief object of which was to obtain the gluten of the wheat in a pure state, as a suitable ingredient in making bread, bis cuits, &c. He works wheat flour into dough by a machine, kneads it, washes out the starch by streams of cold water, a process long known to the chemist, and purifies the starch by fermentation of the superjacent water.
Mr. Jones's patent, of 1840, is based upon the purification of the starch of rice and other farinaceous matters, by means of caustic alkali. He macerates 100 lbs. of ground rice in 100 gallons of a solution composed of 200 grains of caustic soda or potash to a gallon of water, stirs it gra dually, till the whole be well mixed; after 24 hours, draws off the superjacent liquid solution of gluten in alkali, treats the starchy deposit with a fresh quantity of weak caustic ley, and thus repeatedly, till the starch becomes white and pure. The rice before being ground is steeped for some time in a like caustic ley, drain ed, dried, and sent to the mill.