STARCH. This term is appropriated to a substance existing in vegetables, simi lar in many of its properties to gum. It is a dry, white powder, which forms the principal part of the nutritive grains and roots. If a paste be formed of wheaten flour and water, and this be washed with additional quantities of water, till it is no longer turbid, but comes off pure and co lourless, the mass which remains becomes tenacious and ductile. This is called Gramm, which see. If the water with which the paste was washed be allowed to remain at rest, it deposits a white pow der, which is distinguished by the name of fecula or starch. Starch is of a fine white colour, and is usually in the state of concrete columnar masses. It has no per ceptible smell, and scarcely any taste. It is little altered by exposure to the air ; when it is exposed to heat on a hot iron, it melts, swells up, becomes black, and burns with a bright flame. The charcoal which remains contains a little potash. When it is distilled it gives out water mixed with acetic acid, which is contami nated with oil. It gives out also carbonic acid, and carbonated hydrogen gas. Starch is not soluble in cold, but forms a thick paste with boiling water; and when this paste is allowed to cool, it becomes semitransparent atid gelatinous ; it is brit tle when dry, somewhat resembling gum. If this paste be exposed to moist air, it is decomposed, for it acquires an acid taste. Sulphuric acid dissolves starch slowly ; sulphurous acid is disengaged, and a great quantity of charcoal is formed. Muriatic acid also dissolves starch, and the solution resembles mucilage of gum Arabic. When left at rest, a thick, oily, mucilaginous liquid appears above, and a transparent straw coloured fluid below. The odour of muriatic acid remains, but when water is added, it is destroyed, and a strong peculiar smell is emitted. Starch is
also soluble in nitric acid, with the evolu tion of nitrous gas. The solution assumes a green colour, and when heat is applied, the starch is converted into oxalic and malic acids. Some part of the starch, however, is insoluble in, nitric acid, and, when this is separated by filtration, and washed with water, it has a thick, oily ap pearance like tallow, is soluble in alcohol, aret when distilled yields acetic acid, and an oily matter similar to tallow in odour and consistence Starch is insoluble in al cohol, but is soluble in the alkalies; in pure potash it swells up, becomes transparent and gelatinous, and is then susceptible of solution in alcohol. The component parts of starch, as appears by distilling it, and by the action of reagents, are, oxy. Fen, hydrogen, and carbon. Starch ex ists in a great number of vegetable sub stances, but chiefly in the roots and seeds, and particularly those which are employ ed as food. Starch, it is well known, may be obtained from the potatoe. If the po tatoe be grated down, and washed with water till it comes off pure and colour less; this water, being left at rest, de posits a fine white powder, which as. sumes something of a crystallized appear ance, and is heavier than wheat starch. It is generally mixed or combined with other principles, and sometimes so inti mately as not easily to be separated. It is not completely formed, except in cer tain states of vegetation. In nutritive grains it is perfect only when they have attained maturity, before this it is in a state approaching to mucilage, mixed with saccharine matter.