ne and toluene again form the points of departure. By the action of
chlorine upon the vapour of boiling toluene there are obtained, according
to the extent of the action of the chlorine, three liquids of use to the
colour manufacturer. The first of these is benzyl chloride, the second
benzal chloride, and the third benzotrichloride or phenyl chloroform.
Benzyl chloride, it may be remarked in passing, plays the same part in
organic chemistry as methyl chloride, and enables certain compounds to be
benzylated, just in the same way that they can be methylated. The bluer
shade of methyl violet, introduced in 1868, and still manufactured, is a
benzylated derivative. By the action of benzotrichloride on
dimethylaniline in the presence of dry zinc chloride, Oscar Doebner
obtained in 1878 a brilliant green colouring-matter which was manufactured
under the name of "malachite green." It will be remembered that this was
about the time when the Fischers were engaged with their investigations.
These last chemists, by virtue of their scientific results, were enabled
to show that Doebner's green was a member of the triphenylmethane group,
and they prepared the same compound by another method which has enabled
the manufacturer to dispense with the use of the somewhat expensive and
disagreeable benzotrichloride. The Fischers' method consists in heating
dimethylaniline with bitter-almond oil and oxidizing the product thus
formed, when the green colouring-matter is at once produced. This method
brings the technologist into competition with Nature, and we shall see the
result.

Benzoic aldehyde or bitter-almond oil is one of the oldest known products
of the vegetable kingdom, and has from time to time been made the subject
of investigation by chemists since the beginning of the century. It arises
from the fermentation of a nitrogenous compound found in the almond, and
known as amygdalin, the nature of the fermentative change undergone by
this substance having been brought to light by Woehler and Liebig. The
discovery of a green dye, requiring for its preparation a vegetable
product which was very costly, compelled the manufacturer to seek another
source of the oil. Pure chemistry again steps in, and solves the problem.
In 1863 it was known to Cahours that benzal chloride, on being heated with
water or alkali, gave benzoic aldehyde, and in 1867 Lauth and Grimaux
showed that the same compound could be formed by oxidizing benzyl chloride
in the