STARCH.
Starch exists naturally in various kinds of grain, as wheat and barley, and in the roots and tubers of many plants, as potatoes. The process of extracting the starch, and separating it from the other constituents of the seed or root, consists, essentially, of crushing it, and wishing out the starch with cold water; the liquid resulting from this mode of treatment is of a milky whiteness, and deposits starch by sediment. This liquid is passed through five sieves to separate the husks and skins, and when the starch has settled, and the liquid fermented and become sour, it is drawn off; it is allowed to become sour as the gluten of the grain is more completely separated by so doing. The starch is repeatedly stirred, allowed to settle, and the water drawn off, till it is quite pure; the top of the starch is scraped to separate any slime adhering, and the pure starch dug out with wooden shovels and put in a box lined with linen, in which the moisture drains off; the cakes taken from these boxes are cut up into squares, put upon bricks, and dried by a gentle heat; the squares are then scraped clean and packed in paper for sale, in these packages it breaks up into pieces, so that when they are opened, the starch has that peculiar appearance so familiar, and almost resembling six-sided columns. Arrow-root is the starch obtained from a West Indian plant called Maranta Arundinacea.
Cassava and Tapioca are starches from the manioc, and Sago, from the sago palm. Starch, under the microscope, appears in the form of minute globules, and is quite insoluble in cold water, in which it falls to the bottom, leaving the water at the upper part quite clear; but water that is nearly boiling (that is to say at 160 deg. of Fahrenheit’s thermometer, or above), breaks or dissolves the granules, and the starch forms with it a sort of paste, this is the liquid used for stiffening linen and other articles in domestic laundry.
The starch sold in this country is colored blueish by smalt or indigo; but on the continent is used of its natural white color. If starch be baked in an oven at the temperature of about 300 deg. it becomes, to a great extent, soluble in cold water, forming what is called “British gum,” this is largely used for calico printing and other purposes; if boiled in water under great pressure, so that the temperature can be raised to the same degree, it is also changed into an adhesive sort of gum—this is the substance made use of by the government authorities to spread over the backs of postage and receipt stamps to make them adhere. The starch of grain during germination, or growth, becomes converted into sugar; the same effect can be produced by heating starch with diluted sulphuric acid.