dded that the phenol used must be of the
greatest possible purity, and the requirements of the surgeon have been
met by chemical and technological skill.

From surgery back to colouring-matters, and from these to pharmaceutical
preparations and perfumes, are we led in following up the cycles of
chemical transformation which these tar-products have undergone in the
hands of the technologist, guided by the researches of the chemist. It was
observed by Runge in 1834 that crude carbolic acid, on treatment with
lime, gave a red, acid colouring-matter which he separated and named
"rosolic acid." The observation was followed up, and many other chemists
obtained red colouring-matters by the oxidation of crude phenol. In 1859,
the colour-giving property of carbolic acid acquired industrial importance
from a discovery made by Kolbe and Schmitt in Germany, and by Persoz in
France. These chemists found that a good yield of the colouring-matter was
obtained by heating phenol with oxalic and sulphuric acids. Under the
names of "corallin" and "aurin" the dye-stuff was introduced into
commerce, and it is still used for certain purposes, especially for the
preparation of coloured lakes for paper-staining.

The scientific development of the history of this phenol dye is full of
interest, but we can only give it a passing glance. Its interest lies
chiefly in the circumstance that it is related to magenta, as was first
pointed out by Caro and Wanklyn in 1866. In fact they obtained rosolic
acid from magenta by the action of nitrous acid on the latter. We now know
that a diazo-salt is first formed under these circumstances, and that the
decomposition of this unstable compound in the presence of water gives
rise to the rosolic acid. Later researches have shown that by heating
rosolic acid with ammonia it is converted into rosaniline. It is also
known that the commercial corallin, like the commercial magenta, is a
mixture of closely related colouring-matters. The close analogy between
magenta and rosolic acid was further shown by Caro in 1866. In the same
way that Hofmann found that magenta could not be produced by the oxidation
of _pure_ aniline, Caro found that a mixture of phenol and cresol was
necessary for the production of rosolic acid when inorganic oxidizers were
used. It is indeed this series of investigations upon the phenol
dyes--investigations which have been taken part in not only by the
chemists named, but also by Graebe, Dale an