generation.

Foremost among the workers who rendered this epoch of organic chemistry
memorable were Justus Liebig in Germany and Jean Baptiste Andre Dumas
in France, and their respective pupils, Charles Frederic Gerhardt and
Augustus Laurent. Wohler, too, must be named in the same breath, as also
must Louis Pasteur, who, though somewhat younger than the others, came
upon the scene in time to take chief part in the most important of the
controversies that grew out of their labors.

Several years earlier than this the way had been paved for the study
of organic substances by Gay-Lussac's discovery, made in 1815, that a
certain compound of carbon and nitrogen, which he named cyanogen, has a
peculiar degree of stability which enables it to retain its identity and
enter into chemical relations after the manner of a simple body. A year
later Ampere discovered that nitrogen and hydrogen, when combined in
certain proportions to form what he called ammonium, have the same
property. Berzelius had seized upon this discovery of the compound
radical, as it was called, because it seemed to lend aid to his
dualistic theory. He conceived the idea that all organic compounds
are binary unions of various compound radicals with an atom of oxygen,
announcing this theory in 1818. Ten years later, Liebig and Wohler
undertook a joint investigation which resulted in proving that compound
radicals are indeed very abundant among organic substances. Thus the
theory of Berzelius seemed to be substantiated, and organic chemistry
came to be defined as the chemistry of compound radicals.

But even in the day of its seeming triumph the dualistic theory
was destined to receive a rude shock. This came about through the
investigations of Dumas, who proved that in a certain organic substance
an atom of hydrogen may be removed and an atom of chlorine substituted
in its place without destroying the integrity of the original
compound--much as a child might substitute one block for another in
its play-house. Such a substitution would be quite consistent with the
dualistic theory, were it not for the very essential fact that hydrogen
is a powerfully electro-positive element, while chlorine is as strongly
electro-negative. Hence the compound radical which united successively
with these two elements must itself be at one time electro-positive, at
another electro-negative--a seeming inconsistency which threw the entire
Berzelian theory into disfavor.

In its