OH and C_{2}H_{5}OH so obtained belong to the class of substances
known as _alcohols_. From their formulas it will be seen that they may
be regarded as derived from hydrocarbons by substituting the hydroxyl
group (OH) for hydrogen. Thus the alcohol CH_{3}OH may be regarded as
derived from methane (CH_{4}) by substituting the group OH for one atom
of hydrogen. A great many alcohols are known, and, like the
hydrocarbons, they may be grouped into series. The relation between the
first three members of the methane series and the corresponding alcohols
is shown in the following table:

CH_{4} (methane) CH_{3}OH (methyl alcohol).
C_{2}H_{6} (ethane) C_{2}H_{5}OH (ethyl alcohol).
C_{3}H_{8} (propane) C_{3}H_{7}OH (propyl alcohol).

~Methyl alcohol~ (_wood alcohol_) (CH_{3}OH). When wood is placed in an
air-tight retort and heated, a number of compounds are evolved, the most
important of which are the three liquids, methyl alcohol, acetic acid,
and acetone. Methyl alcohol is obtained entirely from this source, and
on this account is commonly called _wood alcohol_. It is a colorless
liquid which has a density of 0.79 and boils at 67 deg.. It burns with an
almost colorless flame and is sometimes used for heating purposes, in
place of the more expensive ethyl alcohol. It is a good solvent for
organic substances and is used especially as a solvent in the
manufacture of varnishes. It is very poisonous.

~Ethyl alcohol~ (_common alcohol_) (C_{2}H_{5}OH). 1. _Preparation._ This
compound may be prepared from glucose (C_{6}H_{12}O_{6}), a sugar easily
obtained from starch. If some baker's yeast is added to a solution of
glucose and the temperature is maintained at about 30 deg., bubbles of gas
are soon evolved, showing that a change is taking place. The yeast
contains a large number of minute organized bodies, which are really
forms of plant life. The plant grows in the glucose solution, and in so
doing secretes a substance known as _zymase_, which breaks down the
glucose in accordance with the following equation:

C_{6}H_{12}O_{6} = 2C_{2}H_{5}OH + 2CO_{2}.

~Laboratory preparation of alcohol.~ The formation of alcohol and
carbon dioxide from glucose may be shown as follows: About 100
g. of glucose are dissolved in a liter of water in flask A
(Fig. 90). This flask is connected with the bottle B, which
is partially filled with limewater. The tube C contains so