r and is the
most important member of the class of compounds called _ethers_.
Ordinarily ether is a light, very inflammable liquid boiling at 35 deg.. It
is used as a solvent for organic substances and as an anaesthetic in
surgical operations.

KETONES

The most common member of this group is acetone (C_{3}H_{6}O), a
colorless liquid obtained when wood is heated in the absence of air. It
is used in the preparation of other organic compounds, especially
chloroform.

ORGANIC BASES

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
(CH_{3}NH_{2}) and ethylamine (C_{2}H_{5}NH_{2}). These two compounds
are gases and are formed in the distillation of wood and bones. Pyridine
(C_{5}H_{6}N) and quinoline (C_{9}H_{7}N) 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 C_{12}H_{22}O_{11}.
Milk sugar C_{12}H_{22}O_{11}.
Dextrose C_{6}H_{12}O_{6}.
Levulose C_{6}H_{12}O_{6}.
Cellulose C_{6}H_{10}O_{5}.
Starch C_{6}H_{10}0_{5}.

~Cane sugar~ (C_{12}H_{22}O_{11}). 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