STARCH. A well-known substance extracted from wheaten flour, by washing it in water. All farinaceous seeds afford this substance in a greater or less degree; but it is most easily obtained from the flour of wheat, by moistening any quantity with a little water, and kneading it with the hand mto a tough paste; this being washed with water by letting fall upon it a very slender stream, the water will be rendered turbid as it runs of in consequence of the fecula or starch which it extracts from the flour, and which will subside when the water is allowed to stand at rest. The starch so obtained, when dried in the sun, or by a stove, is usually concreted into small masses, which have a fine white colour, scarcely any smell, and very little taste. If kept dry, starch in this state continues a long time uninjured, although exposed to the air. The inferior and renew wheat is usually employed for manufacturing common starch; but when the finest starch is required, good grain must be used. This, being well ,cleaned, and sometimes coarsely bruised, is put into wooden vessels full of water, to ferment : to assist the fermentation the vessels are exposed to the greatest heat of the sun, and the water is changed twice a day, during eight or twelve days, according to the season. When the grain bursts easily under the finger, and gives out a milky white liquor when squeezed, it is judged to be sufliciently softened and fermented. In this state the grains are taken out of the water by a sieve, and put into a canvass sack, and the husks are separated and rubbed off by beating and rubbing the sack upon a plank: the sack is then put into a tub filled with cold water, and trodden or beaten till the water becomes milky and turbid, from the starch which it takes up from the grain. A scum sometimes swims upon the surface of the water, which must be care ,fully removed; the water is then run off through a fine sieve into a settling .vessel, and fresh water is poured upon the grains, two or three times, till it will not extract any more starch, or become coloured by the grain. The water in the settling vessels, being left at rest, precipitates the starch, which is had sus pended ; and to get rid of the saccharine matter, which was also dissolved by the water, the vessels are exposed to the sun, which soon produces the acetone lbrmentation, and takes matter as renders the starch more pure and white. When the water es completely sour, it is poured gently off from the starch, which is washed several times afterwards With clean water, and at last is placed to drain upon linen cloths, supported by hurdles, and the water drips through, leaving the starch upon the cloths, in which it is pressed and wrung, to extract as much as possible of the water ; and the remainder is evaporated by cutting the starch into pieces, which are laid up in airy places, upon a floor of plaster, or of slightly burnt bricks, until it becomes completely dried from all moisture, partly the access of warm air, and partly by the floor imbibing the moisture. In winter-time, the beat of a stove must be employed to effect the drying. Lastly, the pieces of starch are scraped to remove the outside crust, which makes inferior starch, and these pieces are broken into smaller pieces for sale. The grain which remains in the sack after the starch is extracted contains the husks and the glutinous part of the wheat, which are found very nutritious food for cattle.
Starch does not dissolve in cold water, but very soon falls to powder, and forms with it a kind of emulsion. It combines with boiling water, and forms with it a thick paste. Linen dipped into this paste acquires, as is well known, a great degree of stiffbess. When the paste is allowed to cool, it assumes the form of a semi-transparent jelly, which, when dried by artificial heat, becomes brittle, and assumes an appearance not unlike that of gum. Hence it is sup posed that starch, by being boilld in water, undergoes a certain degree of decomposition, which brings it nearly to the state of gum. When this paste is left exposed to damp air it soon loses its consistency, acquires an acid taste, and its surface is covered with mould. Starch is so far from dissolving in alcohol, even when assisted by heat, that it does not even fall to powder. The action of the mineral acids upon starch we have not space to detail; we there fore refer the reader to Ure's Dictionary for infbrmation thereon. The alkalies dissolve starch, but their action has not been examined with care. In pure potess it swells, and assumes the appearance of a transparent jelly. In this state the solution is soluble in alcohol. When starch is thrown upon a hot iron, it melts, blackens, froths, smells, and burns with a bright flame like sugar, emitting at the same time a great deal of smoke ; but it does not explode, nor has it the caromel smell which distinguishes burning sugar. When distilled, it yields water, impregnated with an acid supposed to be the pyromucous, a little empyreumatic oil, and a great deal of carbonic acid and carburetted hydrogen gas. The charcoal which remains is easily dissipated when set on fire in the open air,—a proof that it contains very little earth. Barley-grain consists almost entirely of starch ; not, however, in a state of perfect purity. In the process of malting, which is nothing else than causing the barley to begin to vegetate, a great part of the starch is converted into sugar. During this process oxygen gas is absorbed, and carbonic acid gas is emitted. Water, too, is abso lutely necessary ; hence it is probable that it is decomposed, and its hydrogen retained. Starch, then, seems to be converted into sugar by diminishing the proportion of its carbon, and increasing that of its hydrogen and oxygen. Its distillation shows us that it contains no other ingredient than these three. Starch is contained in a great variety of vegetable substances, most commonly in their seeds or bulbous roots, but sometimes also in other parts. Indeed the greater number, if not the whole, of the vegetable seeds employed by man as an article of food consists chiefly of starch. But that substance is always combined with some other which serves to disguise its properties, such as sugar, oil, extractive, &c. It is only by processes similar to those described in the beginnin4 of this article, that it is extracted from these substances in a state of tolerable purity. Starch may be made from potatoes, by soaking them about an hour in water, and taking off their roots and fibres, then rubbing them quite clean by a strong brush ; this they are reduced to a pulp, by grating them in water ; but when this is attempted in a large way, some kind of mill must be used to reduce them to a pulp, as the grating of them by hand is too tedious an operation. A complete mill for this purpose is described under the article