The tubers are washed and peeled, usually by machinery, rasped by a revolving grater, and the pulp washed on hair sieves till freed from the starchy matter. Successive portions of the pulp are thus treated till the vessels over which the sieves are placed is sufficiently full. The starch held in suspension in water, subsides to the bottom; the water is then drawn off, and the starch stirred up with fresh water, and again allowed to subside. This is repeated several times till the starch is sufficiently pure. The fibres and the washing waters are used as manures. The washed fibres have also been recommended as an ingredient in bread for diabetic patients. Wheat Starch. Wheat flour is steeped in water for a week or two and allowed to ferment. The acid liquor is drawn off, and the residue washed on a sieve: what passes through is allowed to settle, the sour liquor drawn off, and the starch thoroughly washed from the slimy matter. It is then drained in perforated boxes, cut up into square lumps, placed on bricks to absorb the moisture, and dried in a stove. See Dr. Pereira's ' Elements.'

Various means are adopted to free the starch from gluten and other impurities. In the patent rice starch, and probably other kinds of starch, alkaline solutions are used. Ammonia has been recommended, as it does not, like potash and soda, dissolve any portion of pure starch.

The various kinds of fecula are distinguishable by the form of their particles or grains. By a microscopical examination of these, the mixture or substitution of potato starch with the more expensive kinds is readily detected. Figures of the different kinds of starch grains are given in the ' Pharmaceutical Journal,' vol. iv, in Dr. Pereira's ' Elements.' In Attfield's 'Chemistry, General, Medical and Pharmaceutical,' etc. M. Gobley has proposed to distinguish them by the coloration produced when the several kinds are exposed to the vapour of iodine; but the effect seems to depend greatly on the relative dryness of the samples.