ferent atoms of the
elements composing a molecule are of different sizes and shapes; on this
point we are as yet profoundly ignorant.

Now as long ago as 1856, at the time when Perkin began making mauve by
oxidizing aniline with bichromate of potash, it was observed by Natanson,
that when aniline was heated with a certain oxidizing agent a red
colouring-matter was produced. The same fact was observed in 1858 by
Hofmann, who used the tetrachloride of carbon as an oxidizing agent. These
chemists obtained the red colouring-matter as a by-product; it was formed
only in small quantity, and was regarded as an impurity. In the same year,
1858, two French manufacturers patented the production of a red dye formed
by the action of chromic acid and other oxidizing agents on aniline, the
colouring matter thus made being used for dying artificial flowers. Then,
a year later, the French chemist Verguin found that the best oxidizing
agent was the tetrachloride of tin, and this with many other oxidizing
substances was patented by Renard Freres and Franc, and under their patent
the manufacture of the aniline red was commenced on a small scale in
France. Finally, in 1860, an oxidizing agent was made use of almost
simultaneously by two English chemists, Medlock and Nicholson, which gave
a far better yield of the red than any of the other materials previously
in use, and put the manufacture of the colouring-matter on quite a new
basis. The oxidizing material patented by Medlock and Nicholson is arsenic
acid, and their process is carried on at the present time on an enormous
scale in all the chief colour factories in Europe, the colouring-matter
produced by this means being generally known as fuchsine or magenta.

In four years the accidental observation of Natanson and Hofmann, made, be
it remembered, in the course of abstract scientific investigation, had
thus developed into an important branch of manufacture. A demand for
aniline on an increased scale sprung up, and the light oils of coal-tar
became of still greater importance. The operations of the tar-distiller
had to undergo a corresponding increase in magnitude and refinement; the
production of nitrobenzene and necessarily of nitric acid had to be
increased, and a new branch of manufacture, that of arsenic acid from
arsenious acid and nitric acid, was called into existence. Perkin's mauve
prepared the way for the manufacture of aniline, and the discovery of a
good process for the pro