Preparation of With regard to the purposes to which starch is applied, the vari ous kinds may be divided into (1) starches used for food and (2) starches used for laundry and other industrial purposes, though certain kinds are extensively used under both of these heads. In their chemical relations all varieties of starch are identical, but in their physical con stitution and microscopic structure they present marked differences, and they also vary much as regards digestibility and suitableness as articles of food. The size of these granules and the arrangement of layers differ in every different species of plant, and, therefore, the source of any particular starch is readily determined by microscopic examination. Starch may be puri fied by freezing a 1 per cent mixture with water and melting the ice. The starch settles and the liquid retains the impurities.
The food starches embrace arrowroot, tous lesmois, sago and tapioca. Corn-starch, which has an enormous sale, is simply the starch of Indian corn or maize separated mechanically from the grain. The process most commonly in use in the United States is known as the sulphur dioxide process. The grain is steeped in a 1 per cent aqueous solution of sulphur dioxide at a temperature of 250° to 300° F. for from two to four days. The swelled grains while wet are then crushed between cylinders under a flow of water, washing the mass through a cylindrical sieve so as to separate out the husky matter. The milk-like fluid which contains the starch in suspension passes through the sieve and is run along a series of gently inclined surfaces, on which the heavier granules are deposited, the lighter and finer particles being carried with nitrogenous matter into settling-tanks. The deposit which accumulates in the settling-tank is purified by repeated straining and settling, and the separated starch is dried by gentle artificial heat, when it crum bles to a powder, and as such it is packed for the market.
Starch for industrial purposes is obtained also from potatoes, wheat and rice, and sago starch is extensively employed for other than food purposes. Starch from many different substances finds occasional or limited employ ment. Potatoes affected by disease yield as pure and useful a starch as sound tubers, but much less in proportion to their weight, as the disease usually results in the transmutation of starch to sugar. On a small scale the prepara tion of starch from potatoes is a simple oper ation. The tubers have simply to be thoroughly washed to free them from all earthy impurity, then rasped down to a fine pulp in a tub of water and allowed to settle, when the starch will fall to the bottom and the greater part of the skin or husk will float on the water. By repeated washing and settling of the starchy deposits the starch may be obtained in a con dition of purity, and it may then be dried by gentle heat for preservation and use. On the manufacturing scale, machinery of various kinds is adapted for performing the several processes of steeping and washing, straining out of stones, rasping, straining, settling, puri fying, draining and drying which the potatoes undergo. Some manufacturers pass the rasp
ings through a grinding mill, resulting in an increase of starch product by 8 to 12 per cent. Beyond its use in industrial pursuits in com mon with other starches, potato-starch is much employed for making imitation sago, for adul terating and as a substitute for the more costly food-starches, for preparing starch-sugar and as a source of potato-spirit.
Wheat-starch is prepared by two distinct processes. By the first and old method the grain is subjected to a process of fermentation whereby the gluten or nitrogenous constituent of the wheat is rendered soluble and the remain der of it loses its adhesive property, and in this condition the starch is easily separated out by a washing wheel or drum. By this process the greater part of the gluten is wasted, and a smaller yield of starch is obtained than can be secured by the more recent system of Martin. The principle on which the latter proceeds can be easily illustrated by making a dough of flour, placing it in a muslin bag and squeezing it under the water, when the starch exudes min gling with the water and settling as a sediment, leaving within the muslin a gray semi-elastic mass consisting chiefly of gluten. In this way the gluten is saved and can be utilized for cattle-feeding, etc. The production is two pounds of starch for each pound of gluten. By whatever process prepared, wheaten starch is purified by repeated washing and settling, and dried by gentle heat, and on drying it assumes the columnar structure by which it is familiarly known.
In the preparation of rice-starch, a variety preferred for laundry purposes, the grain has to be steeped in a slightly alkaline solution on ac count of its peculiarly hard and horny envelope of gluten. In addition to being extensively used in laundries, starch is largely consumed in the manufacture of dextrin (q.v.), and it is also employed as a thickener in calico-printing, and in the finishing of bleached and printed calicoes. Placed in a 2 per cent solution of soda or potash the granules swell, forming a tenacious paste used by photographers for mounting prints and for many other purposes. Dry starch finds a. valuable minor adaptation in dusting molds in metal-casting, besides being applied for many miscellaneous purposes.
Statistics.— In the United States in 1914 there were 82 starch factories, having an in vested capital of $12,070,000. There were 1,780 persons employed and the total value of the product for the year was $13,996,000. In this production New York ranked first, Indiana sec ond and Ohio third. The total quantity of starch manufactured was 620,764,347 pounds. Of this total, 574,247,697 pounds were made from Indian corn, 23,540,472 pounds from potatoes and 22,976,178 pounds from all other materials. A very large quantity of starch was made by the seven glucose factories previous to its conversion into glucose (q.v.). No ac count is made of this in the figures given, as the product did not appear in the markets as starch.