nverting aniline into a sulpho-acid (sulphanilic acid),
diazotising this and combining the diazo-compound with alpha- or
beta-naphthol. The compounds formed are brilliant orange dyes, the latter
being still largely consumed as "naphthol orange." Other dye-stuffs of a
similar nature were introduced by Caro about the same time, and were
prepared from the diazotised sulpho-acid of alpha-naphthylamine combined
with the naphthols. By this means alpha-naphthol gives what is known as
"acid brown," or "fast brown," and beta-naphthol a fine crimson, known as
"fast red," or "roccellin." Diazotised compounds combine also with this
same sulpho-acid of alpha-naphthylamine (known as naphthionic acid), the
first colouring-matter formed in this way having been introduced by
Roussin and Poirrier in 1878. It was prepared by diazotising a
nitro-derivative of aniline, and acting with the diazo-salt on napthionic
acid, and this dye is still used to some extent under the name of "archil
substitute." In 1878, the firm of Meister, Lucius & Bruening of
Hoechst-on-the-Main gave a further impetus to the utilization of
naphthalene by discovering two isomeric disulpho-acids of beta-naphthol
formed by heating that phenol with sulphuric acid. By combining various
diazotised bases with these sulpho-acids, a splendid series of acid
azo-dyes ranging in shade from bright orange to claret-red, and to
scarlets rivalling cochineal in brilliancy were given to the tinctorial
industry.

The colouring-matters introduced in 1878 by the Hoechst factory under the
names of "Ponceaux" of various brands, and "Bordeaux," although to some
extent superseded by later discoveries, still occupy an important
position. Their discovery not only increased the consumption of
beta-naphthol, but also that of the bases which were used for diazotising.
These bases are alpha-naphthylamine and those of the aniline series. The
intimate relationship which exists between chemical science and
technology--a relationship which appears so constantly in the foregoing
portions of this work--is well brought out by the discovery under
consideration. A little more chemistry will enable this statement to be
appreciated.

Going back for a moment to the hydrocarbons obtained from light oil, it
will be remembered that benzene and toluene have thus far been considered
as the only ones of importance to the colour-maker. Until the discovery
embodied in the patent specification of 1878, the portions of