Chapter 95

CARBO-HYDRATES.

319. Carbon and Water.--Some very important organic compounds have H and O, in the proper proportion to form water, united with C. The three leading ones are sugar, C12H22O11 or C12(H2O)11, starch, C6H10O6, or ?, and cellulose, C18H30O15 or ?. Note the significance of the name carbo-hydrates as applied to them.

320. Sugars may be divided into two classes,--the sucroses, C12H22O11, and the glucoses, C6H12O6. Sucrose, the principal member of the first class, is obtained from the juice of the maple, the palm, the beet and the sugarcane; in Europe largely from the beet, in America from cane. Granulated sugar is that which has been refined; brown sugar is the unrefined. From the sap evaporated by boiling, brown sugar crystallizes, leaving molasses, which contains glucose and other substances. Good molasses has but a small percentage of glucose. To refine brown sugar it is dissolved in water, a small quantity of blood is added to remove certain vegetable substances, after which it is filtered through animal charcoal, i.e. bone-black, a process which takes out the coloring-matter. The water is then evaporated in vacuum-pans, so as to boil at about 74 degrees and to prevent conversion into grape sugar. By this process much glucose or syrup is formed, which is separated from the crystalline sucrose by rapidly revolving centrifugal machines. Great quantities of sucrose are used for food by all civilized nations. A single refinery in New York purifies 2,000,000 pounds per day.

321. Glucose, or invert sugar, the principal member of the second class, consists of two distinct kinds of sugar, --dextrose and levulose. These differ in certain properties, but have the same symbol. Both are found in equal parts in ripe fruits, while sucrose occurs in the unripe. Honey contains these three kinds of sugar.

Sucrose, by the action of heat, weak acids, or ferments, may be resolved into the other two varieties. C12H22O11 + H2O = C6H12O6 + C6H12O6. No mode of reversing this process, or of transforming glucose into sucrose is known. Glucose is easily made from starch or from the cellulose in cotton rags, sawdust, etc. If boiled with dilute H2SO4 starch takes up water and becomes glucose. C6H10O5 + H2O = C6H12O6.

CaCO3 is added to precipitate the H2SO4, which remains unchanged. State the reaction. The product is filtered and the filtrate is evaporated. Much glucose is made from the starch of corn and potatoes.

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.

327. Zylonite and Celluloid. -These two similar substances embody the latest use of cellulose in manufactured articles. For zylonite, linen paper is cut into strips two feet by one inch, soaked ten minutes in a mixture of H2SO4 and HNO3, a process called nitration, washed for several hours, then ground to a fine pulp, and thoroughly dried. It is then similar to pyroxiline. Aniline coloring-matter of any desired shade is added, after which it is dissolved by soaking some hours in alcohol and camphor, the liquid is evaporated, and the substance is kneaded between steam-heated iron rollers, dried with hot air, and finally subjected to great pressure, to harden it, and cut into sheets. Zylonite is combustible at a low temperature, and when in the pyroxiline stage, explosively so. Ivory, coral, amber, bone, tortoise shell, malachite, etc., are so closely imitated that the imitation can only be detected by analysis. Collars, combs, canes, piano-keys, and jewelry, are manufactured from it, and it can be made transparent enough for windows.