STARCH, a proximate principle exclusively of the vegetable kingdom with the formula Co11,00,0. The value of n has not been de termined but all experiments go to show that it is large — not less than 100, and that, therefore, the molecular weight of starch is at least 32,400. It is found in almost every plant at some period of its life-history, and is especially abundant in wheat, potatoes, arrowroot and other similar kinds of vegetation, and forms a very large and important part of the food of man and the herbivorous animals. It occurs in the ovule of the seed, in the cotyledons of the embyro, in the pith, the bulbs, stems and notably in the roots and tubers of certain families of plants, as the potato, sweet potato, cassava, etc. The starch granules are found in the growing plant in the protoplasm of the chlorophyll corpuscles, varying according to the time of day, being in greatest numbers toward evening and fewest in the morning, sometimes disappearing entirely during the night. Appearing at first as simple points, they gradually increase in size, so that eventually they fill completely the chlorophyll corpuscle, the latter appearing as simply an envelope for the starch. The starch granules grow and increase in size only when in contact with protoplasm and under conditions of ex posure to light at a favorable temperature and in the presence of carbon dioxide. These gran ules are of widely varying sizes in different plants, ranging from a diameter of 0.0069 inch in the canna and 0.0055 inch in the potato, to 0.0003 inch in the parsnip and 0.0002 in the seeds of the beet. Starch appears to be formed in plants in greatest quantity when there is a large supply of nutriment, and it disappears when the nutriment becomes deficient. The amount of starch in various alimentary sub stances is exhibited in the table following.
Starch is a soft, white, shining powder, in soluble in cold water, alcohol or ether; under the microscope it is seen to consist of granules, each of which is formed of a series • of stratified envelopes concentrically arranged round a corn mon nucleus, the outer ones being the denser. Inasmuch as these layers or envelopes are of variable thickness they cause the granule to assume more or less a flattened ovoid form.
Occasionally there are two nuclei within the outer envelope, each surrounded with its own series of concentric layers. The outer layer is the first formed and is known as ((starch cel lulose; the interior is called egranulose.* These two substances may be separated by ap propriate chemical action. Starch dried at ordinary temperatures always retains an amount of water varying from 12 to 18 per cent; but by drying in a vacuum over sulphuric acid and gradually raising the temperature to 212° F. it may be obtained perfectly free from water; but if it be boiled with water the starch gran ules are swollen and broken up, so that on cooling, a stiff, gelatinous mass, starch-paste, is produced; on largely diluting this paste with water, the swollen granules for the most part subside, but a considerable quantity of starch re mains in solution. By boiling starch mixed with a quantity of water, under pressure, at a tem perature of about 300° F., ittis mostly dissolved, and on filtering the liquid and allowing it to cool small granules of starch are deposited, which are slightly soluble in cold water, and are at once dissolved by water heated to 160°. This modification of starch is known as soluble starch. The simplest method of making soluble starch is to dissolve it in hot glycerine. Starch may be detected by boiling the suspected sub stance with water, cooling and adding tinc ture of iodine, when, if starch be present, a fine deep blue color is produced; this color is dissipated by heat or by substances such as alcohol, ether, etc., which dissolve and so re move the iodine.
Nitric acid acts on starch in different ways, according to the strength of the acid used and the temperature. Cold concentrated nitric acid forms a substitution product, i in which one hy drogen atom of the starch s replaced by the group NO,. A mixture of concentrated nitric and sulphuric acid gives rise to the formation of a dinitro-substitution product, in which two atoms of hydrogen are replaced by the group NO, twice. Hot nitric acid converts starch into oxalic, malic and acetic acids. Acted upon for 24 hours by a 12 per cent solution of hydro chloric acid, the starch becomes soluble in water without forming a paste.