Potato starch, or farina, is obtained from the tubers by reducing them to a pulp and mixing well with water. The water carries away the starch, and when allowed to stand the starch falls to the bottom of the vessel and the water can be drawn away. Farina is much used in all kinds of sizing, on account of its cheapness and the thickness of the paste it produces when boiled with water.

Sago is much used in light sizing, for which it is specially adapted. It is obtained from the pith of the sago palm, and made into flour by treating with water and drying on hot plates.

Maize is a starch obtained from the Indian corn, and is sometimes used for lightly sizing the finer counts of cotton yarns.

For light sizing it is not necessary to use anything but wheat flour, farina, or sago, and a small quantity of softening material, usually tallow or wax. Wheat flour is fermented before using by mixing it well with water (about equal weights of each) and leaving it for several weeks, occasionally stirring to keep the particles in suspension. When flour is fermented new bodies are formed, which have a powerful influence in preventing mildew. The fermenting cistern, 1 ([Fig. 22]), is usually a large vessel 8 feet by 4 feet by 4 feet, in which are two revolving “dashers,” C, to stir the flour and water when fermenting. Another similar cistern, 2, is used for storing called a “storage and diluting” cistern, into which the mixture is pumped after a few days, and left to further ferment. A force-pump, N, is used for pumping from this to the mixing cistern, 3, where the softening and weighting materials are added, after being boiled together in pan 4.

FIG. 22.

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Softening materials are used to render the yarn more pliable. The articles mostly used for this purpose are tallow, wax, and soap, cocoanut and palm oil.