To whiten the starches made from damaged roots and grains, and the coarser portions of those from sound ones, a little solution of chloride of lime is occasionally added to the water, followed by another water containing a very little dilute sulphuric acid; every trace of the last being afterwards removed by the copious use of pure soft or spring water.
The bluish-white starch used by laundresses is coloured with a mixture of smalts and alum in water, and is regarded as unfit for medicinal purposes.
Prop., &c. Starch is insoluble in cold water, and in alcohol and most other liquids, but it readily forms a gelatinous compound (amidin) with water at about 175° Fahr.; alcohol and most of the astringent salts precipitate it from its solutions; infusion of galls throws down a copious yellowish precipitate, containing tannic acid, which is redissolved by heating the liquid; heat and dilute acids convert it into dextrin and grape sugar; strong alkaline lyes dissolve it, and ultimately decompose it. Sp. gr. 1·53.
To the naked eye it presents the appearance of a soft, white, and often glistening powder; under the microscope it is seen to be altogether destitute of crystalline structure, but to possess, on the contrary, a kind of organisation, being made of multitudes of little rounded transparent bodies, upon each of which a series of depressed parallel rings, surrounding a central spot or hilum, may be traced. The starch granules from different plants vary both in magnitude and form. Those of potato starch and canna starch (tous les mois) are the largest, and those of rice and millet starch the smallest, the dimensions ranging from 1⁄200 to the 1⁄10000 of an inch. The granules of arrow-root and tous les mois are ovoid, those of potato starch both oblong and circular those of tapioca muller-shaped, and those of wheat starch circular.
Identif. One of the commonest frauds practised upon the profession and the public is the admixture of the cheaper kinds of starch, chiefly potato farina, with arrow-root, and vending manufactured for genuine tapioca, sago, and other articles of diet, used
for invalids and children. These sophistications are most easily detected with a good microscope.[193]
[193] Drawings of the principal starches will be found under the substances from which they are obtained, as “arrow-root,” &c.
Starch, I′odide of. Syn. Amyli iodidum, Amyli iodatum, L. Prep. (Ph. Castr. Ruthena.) Iodine, 24 gr.; rectified spirit, a few drops; rub them to a powder; then add of starch, 1 oz., and again triturate, until the mass assumes a uniform colour. Recommended by Dr A. Buchanan, of Glasgow, as producing the alterative effects of iodine, without the usual irritant action of that medicine.—Dose. A teaspoonful, or more, in water-gruel, or any bland liquid, twice or thrice a day.
Starch, Soluble Iodide of. (Petit.) Prep. Iodine, 12 grammes; starch, 100 grammes; ether, q. s. Dissolve the iodine in the ether, pour the resulting solution over the starch, and triturate until the ether has sufficiently evaporated. Put the product in a porcelain capsule and expose it to the heat of a boiling water bath for half an hour, with occasional stirring. This treatment is sufficient to render it entirely soluble in hot water.
Dr Bellini strongly recommends iodide of starch as a valuable antidote in cases of poisoning by caustic alkalies, alkaline, or earthy sulphides, and vegetable alkaloids. The advantages attending its employment, he says, are: that it may be administered in large doses; that it does not possess the irritating properties of free iodine; and that it readily forms harmless compounds with the substances named. To avoid the subsequent decomposition of the latter, he advises its administration to be followed by an emetic. As an antidote to alkaline and earthy sulphides, the author thinks it preferable to all others. In cases of poisoning by ammonia, caustic potash, or soda, it is applicable when acid drinks are not on hand.