Wood-tar Blue
:
ON THE PRIMARY, BLUE.
The colours obtained from coal-tar have become household words, and it
is not impossible that those from wood-tar may be some day equally
familiar. At present wood-tar is comparatively unexplored, but the fact
that picamar furnishes a blue is at least as suggestive and hopeful as
that transient purple colouration by which aniline was once chiefly
distinguished. As aniline is a product of coal-tar, so picamar is a
product of wood-tar; and as the former gives a purple with
hypochlorites, so the latter yields a blue with baryta-water. Both are
distinguished by coloured tests, but there is this advantage in the
picamar blue--it is comparatively permanent.
Picamar blue is produced when a few drops of baryta-water are added to
an alcoholic solution of impure picamar, or even to wood-tar oil
deprived of its acid. The liquor instantly assumes a bright blue tint,
which in a few minutes passes into an indigo colour. From [Greek: pitta]