322. Starch is found in all plants, especially in grains, seeds, and tubers. Green plants--those containing chlorophyll-- manufacture their own starch from CO2 and H2O. These chlorophyll grains are the plant's chemical laboratories, and hundreds of thousands of them exist in every leaf. CO2 and a very little H2O enter the leaf from the air, H2O being also drawn up through the root and stem from the earth. In some unknown way in the leaf, light has the power of synthesizing these into starch and setting free O, which is returned to the atmosphere.6 CO2 + 5 H2O = C6H10O5 + 12 O. As no such change takes place in darkness, all green plants must have light. Parasitic plants, which are usually colorless, obtain starch ready-made from those on which they feed. 323. Uses.--Glucose is used in the manufacture of alcohol and cheap confectionery, and in adulterating sucrose. It is only two- thirds as sweet as the latter. The seeds of all plants contain starch for the germinating sprout to feed upon; but starch is insoluble, and hence useless until it is converted into glucose. This is effected by the action of warmth, moisture, and a ferment in the seed. Glucose is soluble and is at first the plant's main food. Commercial starch is made in the United States chiefly from corn; in Europe, from potatoes. Differences in the size of starch granules enable microscopists to determine the plant to which they belong. 324. Cellulose, or woody fiber, is the basis of all vegetable cell walls. Cotton fiber represents almost pure cellulose. From it are made paper and woven tissues. In paper manufacture, woody fiber is made into a pulp, washed, bleached, filtered, hot- pressed, and sometimes glazed. Parchment paper, vegetable parchment, is made by dipping unglazed paper for half a minute into cold dilute H2SO4, 1 part H2O, 2 1/2 parts H2SO4, and then washing. The fiber, by chemical change, is thus toughened. The cell walls of wood are impure cellulose; hence the inferior quality of paper made from wood-pulp. Paper is now employed for a large number of purposes for which wood has heretofore been used, such as for barrels, pails, and other hollow ware, wheels, etc. 325. Gun-cotton is made by treating cotton fiber with H2SO4 and HNO3, washing and drying. To all appearances no change has taken place, but the substance has become an explosive compound. 326. Dextrin, a gummy substance used for the backs of postage stamps, is a carbo-hydrate, as in fact are gums in general. Dextrin is made by heating starch with H2SO4 at a lower temperature than for dextrose.