If we soak thin slices of raw potato in cold water, after a while we find a sediment in the pan. This is starch, which has dropped out of the cells which were cut by slicing. This sediment may be purified and dried, and then it will be like the pure starch of commerce.

Pure starch is a fine white powder, and is found enclosed in cells in the various grains, seeds, and vegetables.

We will wet a teaspoonful of cornstarch with a little cold water. It appears to mix with the water, but after standing a short time the starch is found at the bottom of the bowl, and the water is clear again, showing that it has not united with the starch; but by stirring this wet starch till a smooth paste is formed, and pouring it quickly into boiling water, we find that the membranes of the starch grains swell and burst,.and the fine powder inside unites with the boiling water.

We learn from this experiment that cold water does not affect starch; and that boiling water is absorbed by the starch grains, causing them to swell and burst, and form a thick, sticky mass, which, when cold, is quite stiff. Starch is from the German word, stärke, meaning " stiff."

This experiment teaches us the first important principle of mixing dry and liquid ingredients; and also the rule for boiling starchy foods: Any starchy food in the form of a powder, like flour or cornstarch, when it is to be used as a thickening, should first be wet with a little cold water to form a smooth paste. Then add more cold water until it is thin enough to pour. Stir it quickly into rapidly boiling water, and the grains will burst uniformly.

If boiling water be poured upon fine dry starch, the grains are so compact it will not reach all of them. Some will burst more quickly than others, some will not burst at all, and the mass will be lumpy.

But all other starchy foods, like whole grains, vegetables, tapioca, etc., should be put directly into boiling water.

Starch in its uncooked, insoluble state is unwholesome. All starchy foods should be moistened with a sufficient amount of liquid, and subjected to a great degree of heat, that all the grains may swell and burst.