duction of magenta increased this branch of
manufacture to a remarkable extent. Still later in the history of the
magenta manufacture, attempts were made, with more or less success, to use
nitrobenzene itself as an oxidizing agent, and a process was perfected in
1869 by Coupier, which is now in use in many factories.

The introduction of magenta into commerce marks an epoch in the history of
the coal-tar colour industry--pure chemistry and chemical technology both
profited by the discovery. The brilliant red of this colouring-matter is
objected to by modern aestheticism, but the dye is still made in large
quantities, its value having been greatly increased by a discovery made
about the same time by John Holliday and the Baden Aniline and Soda
Company, and patented by the latter in 1877. Magenta is the salt of a base
now known as rosaniline, and it belongs therefore to the class of basic
colouring-matters. The dyes of this kind are as a group less fast, and
have a more limited application than those colouring-matters which possess
an acid character, so that the discovery above referred to--that magenta
could be converted into an acid without destroying its colouring power by
acting upon it with very strong sulphuric acid--opened up a new field for
the employment of the dye, and greatly extended its usefulness. In this
form the colouring-matter is met with under the name of "acid magenta."

It must be understood that the production of magenta from aniline by the
oxidizing action of arsenic acid or nitrobenzene is the result of chemical
change; the colouring-matter is no more present in the aniline than the
latter is contained in the benzene. And just in the same way that the
colourless aniline oil by chemical transformation gives rise to the
intensely colorific magenta, so the latter by further chemical change can
be made to give rise to whole series of different colouring-matters, each
consisting of definite chemical compounds as distinct in individuality as
magenta itself. Thus in 1860, about the time when the arsenic acid process
was inaugurated, two French chemists, Messrs. Girard and De Laire,
observed that by heating rosaniline for some time with aniline and an
aniline salt, blue and violet colouring-matters were produced. This
observation formed the starting-point of a new manufacture proceeding from
magenta as a raw material. The production of the new colouring-matters was
perfected by various investigators, and a