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.