. By the action of this base on
a certain compound ether derived from acetic acid, which is known as
aceto-acetic ether, there is formed a product termed "pyrazole," and this
on methylation gives the alkaloid in question, which is now well known in
pharmacy under the name of "antipyrine."

While dealing with this first industrial application of a hydrazine, it
must be mentioned that the original process by which Fischer prepared
these bases was improved upon by Victor Meyer and Lecco in 1883, who
discovered the use of a cold solution of stannous chloride for reducing
the diazo-chloride to the hydrazine. By this method the manufacture of
phenylhydrazine and other hydrazines is effected on a large scale--all
kinds of amido-compounds and their sulpho-acids can be diazotised and
reduced to their hydrazines. Out of this discovery has arisen the
manufacture of a new class of colouring-matters related to the azo-dyes.
The hydrazines combine with quinones and analogous compounds with the
elimination of water, the oxygen coming from the quinone, and the hydrogen
from the hydrazine. The resulting products are coloured compounds very
similar in properties to the azo-dyes, and one of these was introduced in
1885 by Ziegler, under the name of "tartrazine." The latter is obtained by
the action of a sulpho-acid of phenylhydrazine on dioxytartaric acid, and
is a yellow dye, which is of special interest on account of its
extraordinary fastness towards light.

Another direction in which coal-tar products have been utilized is in the
formation of certain aromatic compounds which occur in the vegetable
kingdom. Thus the artificial production of bitter-almond oil from toluene
has already been explained. By heating phenol with caustic alkali and
chloroform, the aldehyde of salicylic acid, _i.e._ salicylic aldehyde, is
formed, and this, on heating with dry sodium acetate and acetic anhydride,
passes into _coumarin_, the fragrant crystalline substance which is
contained in the Tonka bean and the sweet-scented woodruff. Furthermore,
the familiar flavour and scent of the vanilla bean, which is due to a
crystalline substance known as vanillin, can be obtained from coal-tar
without the use of the plant. The researches of Tiemann and Haarman having
shown that vanillin is a derivative of benzene containing the aldehyde
group, one hydroxyl- and one methoxy-group, the synthesis of this compound
soon followed (Ulrich, 1884). The starting-point in this