NITRO DERIVATIVES OF PHENOL 473of it can be found in alchemical writings of 1742, in which Glauber’s experiments
are described. He acted with nitric acid on wool or horn and isolated picric acid
in the form of its lead or potassium salt. A more detailed description was given
by Woulfe [l] in 1771, who prepared picric acid from indigo by treating it with
nitric acid and found that the new substance had dyeing properties (“indigo yellow”).
while Haussmann [2], in 1788, proved that it behaved like an acid. Later, many workers
obtained the same product by acting with nitric acid on various organic substances,
such as silk, natural resins etc. (Welter [3]; Braconnot [4]). Chevreul [5] was the
first to express the opinion that picric acid contained certain constituents of nitric
acid and this was later confirmed by Dumas [6] and Marchand [7]. The latter gave
C 12 H 6 N 6 O 14 as the empirical formula of picric acid which is exactly double the
correct formula.
Some of the authors had drawn attention to the explosive character of picric
acid salts, but it was not until 1830 that Welter [3] suggested the possibility of apply-
ing picrates as explosives. At that time picric acid was obtained solely by acting with
nitric acid on indigo. Marchand [7] expressed the view, which proved to be true.
that it was aniline, formed as an intermediate product in the process of decom-
position of indigo, silk and other organic matter, which yielded picric acid under
the influence of nitric acid.
The constitution of picric acid was determined by Laurent [8] in 1841. He pre-
pared it by reacting phenol with nitric acid. He was also able to isolate dinitro-
phenol formed in an intermediate stage of the nitration. A further improvement
in the method of preparation of picric acid from phenol was its sulphonationprior to nitration (Schmidt and Glutz [9]).
In the second half of the nineteenth century, picric acid was very widely used as
a fast dye for silk and wool. The first definite suggestions as to the application of
picric acid for the manufacture of explosives go back to the early second half of
the nineteenth century. They referred to the application of picric acid salts as by then
the explosive properties of picrates were already well known. Thus, for example,
Designolle [10] suggested potassium picrate, and Brugere [11] ammonium picrate
as propellants (Vol. III), while in 1871 Abel [12] proposed ammonium picrate as
a high explosive. At that time potassium picrate was already being used in Great
Britain and in the U.S.A. for filling shells.
The view then prevailed, supported by such an authority as Abel, that picric
acid itself is not an explosive but only its salts are. Nevertheless in 1873 Sprengel
[13] proved that picric acid could be brought to explosion by a detonator and
Turpin [14] proposed applying this property of picric acid by utilizing it for filling
shells. In Russia methods of preparation of picric acid and using it as a shell filling
were worked out near 1894 by Panpushko [15]. Eventually picric acid was accepted
all over the world as the basic high explosive for military uses.
Since picric acid melts at high temperature, shells are loaded by pouring it in.
mixed with various nitro compounds: dinitrophenol, mono- and di-nitronaph-
thalenes, TNT, TNX etc. (Vol. III).