arts of living organisms were built up under
the influence of the life force of the organism. Such substances,
therefore, should be regarded as different from those compounds prepared
in the laboratory or formed from the inorganic or mineral constituents
of the earth. In accordance with this view organic chemistry included
those substances formed by living organisms. Inorganic chemistry, on the
other hand, included all substances formed from the mineral portions of
the earth.

In 1828 the German chemist Woehler prepared urea, a typical organic
compound, from inorganic materials. The synthesis of other so-called
organic compounds followed, and at present it is known that the same
chemical laws apply to all substances whether formed in the living
organism or prepared in the laboratory from inorganic constituents. The
terms "organic" and "inorganic" have therefore lost their original
significance.

2. _Present significance._ The great majority of the compounds found in
living organisms contain carbon, and the term "organic chemistry," as
used at present, includes not only these compounds but all compounds of
carbon. _Organic chemistry_ has become, therefore, _the chemistry of the
compounds of carbon_, all other substances being treated under the head
of inorganic chemistry. This separation of the compounds of carbon into
a group by themselves is made almost necessary by their great number,
over one hundred thousand having been recorded. For convenience some of
the simpler carbon compounds, such as the oxides and the carbonates, are
usually discussed in inorganic chemistry.

~The grouping of compounds in classes.~ The study of organic chemistry is
much simplified by the fact that the large number of bodies included in
this field may be grouped in classes of similar compounds. It thus
becomes possible to study the properties of each class as a whole, in
much the same way as we study a group of elements. The most important of
these classes are the _hydrocarbons_, the _alcohols_, the _aldehydes_,
the _acids_, the _ethereal salts_, the _ethers_, the _ketones_, the
_organic bases_, and the _carbohydrates_. A few members of each of these
classes will now be discussed briefly.

THE HYDROCARBONS

Carbon and hydrogen combine to form a large number of compounds. These
compounds are known collectively as the _hydrocarbons_. They may be
divided into a number of groups or series, each being named from its
first member. Some of the