Fig. 428.—Plantation of sugar-canes.
If starch be baked in an oven at a temperature of about 300° 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, “mucilage”; this is the substance made use of by the government officials to spread over the backs of postage and receipt stamps to make them adhere. The starch of grain, during germination, or growth, contains diastase, which converts the starch into gum and sugar; the same effect can be produced by heating starch with diluted sulphuric acid.
Gum found in plants is chiefly procured from the Mimosa trees, from which it flows in drops, and is called Gum Arabic. There are other so-called “gums,” but this is the one generally referred to.
Sugar exists in fruits, roots, and in the stalks of plants, in the juice of the cane, maple, and beet-root particularly. The canes are crushed, the juice is clarified with lime to prevent fermentation, and the liquid is evaporated. It is then granulated and cleared from the molasses. Sugar, when heated, becomes dark, and is called “caramel.” It is used for colouring brandy, and gives much difficulty to the sugar refiners.
Fig. 429.—Refining vacuum pan.
Fig. 430.—Sugar moulds.
