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:

C_{12}H_{22}O_{11} + H_{2}O = C_{6}H_{12}O_{6} + C_{6}H_{12}O_{6}.

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 deg. cane sugar melts; if the temperature is increased to
about 215 deg., a partial decomposition takes place and a brown substance
known as caramel forms. This is used largely as a coloring matter.

~Milk sugar~ (C_{12}H_{22}O_{11}). This sugar is present in the milk of
all mammals. The average composition of cow's milk is as follows:

Water 87.17%
Casein (nitrogenous matter) 3.56
Butter fat 3.64
Milk sugar 4.88
Mineral matter 0.75

When _rennin_, an enzyme obtained from the stomach of calves, is added
to milk, the casein separates and is used in the manufacture of cheese.
The remaining liquid contains the milk sugar which separates on
evaporation; it resembles cane sugar in appearance but is not so sweet
or soluble. The souring of milk is due to the fact that the milk sugar
present undergoes _lactic fermentation_ in accordance with the equation

C_{12}H_{22}O_{11} + H_{2}O = 4C_{3}H_{6}O_{3}.

The lactic acid formed causes the separation of the casein, thus giving
the well-known appearance of sour milk.

~Isomeric compounds.~ It will be observed that cane sugar and milk sugar
have the same formulas. Their difference in properties is due to the
differe