This group includes a number of compounds, all of which contain nitrogen as well as carbon. They are characterized by combining directly with acids to form salts, and in this respect they resemble ammonia. They may, indeed, be regarded as derived from ammonia by displacing a part or all of the hydrogen present in ammonia by hydrocarbon radicals. Among the simplest of these compounds may be mentioned methylamine (CH3NH2) and ethylamine (C2H5NH2). These two compounds are gases and are formed in the distillation of wood and bones. Pyridine (C5H6N) and quinoline (C9H7N) are liquids present in small amounts in coal tar, and also in the liquid obtained by the distillation of bones. Most of the compounds now classified under the general name of alkaloids (which see) also belong to this group.
CARBOHYDRATES
The term "carbohydrate" is applied to a class of compounds which includes the sugars, starch, and allied bodies These compounds contain carbon, hydrogen, and oxygen the last two elements generally being present in the proportion in which they combine to form water. The most important members of this class are the following:
| Cane sugar | C12H22O11. |
| Milk sugar | C12H22O11. |
| Dextrose | C6H12O6. |
| Levulose | C6H12O6. |
| Cellulose | C6H10O5. |
| Starch | C6H1005. |
Cane sugar (C12H22O11). This is the well-known substance commonly called sugar. It occurs in many plants especially in the sugar cane and sugar beet. It was formerly obtained almost entirely from the sugar cane, but at present the greatest amount of it comes from the sugar beet. The juice from the cane or beet contains the sugar in solution along with many impurities. These impurities are removed, and the resulting solution is then evaporated until the sugar crystallizes out. The evaporation is conducted in closed vessels from which the air is partially exhausted. In this way the boiling point of the solution is lowered and the charring of the sugar is prevented. It is impossible to remove all the sugar from the solution. In preparing sugar from sugar cane the liquors left after separating as much of it as possible from the juice of the cane constitute ordinary molasses. Maple sugar is made by the evaporation of the sap obtained from a species of the maple tree. Its sweetness is due to the presence of cane sugar, other products present in the maple sap imparting the distinctive flavor.
When a solution of cane sugar is heated with hydrochloric or other dilute mineral acid, two compounds, dextrose and levulose, are formed in accordance with the following equation:
C12H22O11 + H2O = C6H12O6 + C6H12O6.
This same change is brought about by the action of an enzyme present in the yeast plant. When yeast is added to a solution of cane sugar fermentation is set up. The cane sugar, however, does not ferment directly: the enzyme in the yeast first transforms the sugar into dextrose and levulose, and these sugars then undergo alcoholic fermentation.
When heated to 160° cane sugar melts; if the temperature is increased to about 215°, a partial decomposition takes place and a brown substance known as caramel forms. This is used largely as a coloring matter.
Milk sugar (C12H22O11). This sugar is present in the milk of all mammals. The average composition of cow's milk is as follows: