The Chemistry of Powder and Explosives - Sciencemadness Dot Org

164 AROMATIC NITRO COMPOUNDS
the action of nitric acid on indigo yielded a material which dyed
sulk yellow. Hausmann 57 isolated the substance in 1778, and
reported further studies upon it in 1788, noting particularly its
bitter taste. Welter 58 in 1799 obtained picric acid by the action of
nitric acid on silk, and the material came to be known generally
as "Welter's bitter." Its preparation from indigo, aloes, resin,
and other organic substances was studied by many chemists,
among them Fourcroy and Vauquelin, Chevreul, Liebig, Wohler,
Robiquet, Piria, Delalande, and Stenhouse. Its preparation from
oil of eucalyptus was suggested during the first World War. It
was given the name of acide picrique by Dumas; cf. Greek
iriKpds = bitter, old English puckery. Its relation to phenol was
demonstrated in 1841 by Laurent, 39 who prepared it by the nitration
of that substance, and its structure was proved fully by
Hepp, 60 who procured it by the oxidation of sj/m-trinitrobenzene.
Picric acid is a strong acid; it decomposes carbonates and may
be titrated with bases by the use of sodium alizarine sulfonate
as an indicator. It is a fast yellow dye for silk and wool. It attacks
the common metals, exr.ept aluminum and tin, and produces
dangerously explosive salts. Cordeau Lheure, which was long
used extensively in France, was made by filling a tin pipe with
fused picric acid and later drawing down to the desired diameter.
It had the disadvantage that the metal suffered from the "tin
disease," became unduly brittle, and changed to its gray allotropic
modification. Picric acid and nitrophenols, when used in
ammunition, are not allowed to come in contact with the metal
parts. Shells which are to be loaded with these explosives are
first plated on the inside with tin or painted with asphaltum
varnish or Bakelite.
Dupre 61 in 1901 reported experiments which indicated that the
picrates of calcium, lead, and zinc, formed in situ from melted
picric acid are capable of initiating the explosion of that material.
Kast 62 found that the dehydrated picrates are more sensitive than
those which contain water of crystallization. The data tabulated
57
J. Phys. 32, 165 (1788).
**Ann. chim. phys., I, 29, 301 (1799).
59
Ann. chim. phys., Ill, 3, 221 (1841).
60
Hepp, loc. cit.
01
Mem. poudres, 11, 92 (1901).
62
Z. ges. Schiess- it. Sprengstoffw., 6, 7, 31, 67 (1911). See also Will, ibid.,
1, 209 (1906); Silberrad and Phillips, /. Chem. Soc, 93, 474 (1908).