A Manual of the Chemistry of the Carbon Compounds

THE CARBON COMPOUNDS. 411
green needles. The salts of this ammonium-base dye on silk a rich
reddish-violet shade.
Zeueanilinc C20Hj,N8.—The salts of this base are formed by treating
rosaniline-salts with reducing agents. They are colourless, and
readily oxidized to rosaniline-salts.
GlmjsanUi-M C^H^N,, is obtained as a bye-product in the manufacture
of rosaniline. It is a yellow amorphous powder, and forms two
series of yellow crystalline salts, containiag either one or two equivalents
of an acid.
JCylidim-rei C^H^Ng.—Neither xylidine alone nor mixed with
toluidino yields a colour, but when- a mixture of aniline and xylidine
is heated with arsenic acid, a red compound is produced, having the
greatest resemblance to rosaniline.
PHENOL-COLOURS.
"When phenols are heated with polybasie organic acids, either alone
or in presence of sulphuric acid or glycerin, water is eliminated, and
a series of peculiar compounds is formed, some being neutral bodies,
while others dissolve in alkalis, forming intensely-coloured solutions,
which are decolourized by reducing agents.
Some of the coloured bodies yield, when heated with sulphuric
acid, new colours, which are also readily reduced in an alkaline solution,
but not decolourized. The number of these compounds seems
to be unlimited, but only a few have been more minutely studied.
Aurin O20H,.O8.—This compound is found in commerce under the
name of " corallin," or " rosolio acid," 1 and is used for dyeing silk and
wool. It is prepared by heating phenol with oxalic acid and sulphuric
acid. The commercial product is a brittle, resinous body,
having a beetle-green lustre, and yieldiug a red powder. It is a mixtare
of different bodies; to obtain pure aurin from it, an alcoholic
solution of ammonia is added to a cold concentrated alcoholic solution
ot' the crude substance. A crystalline precipitate, a compound of
aurin with ammonia, separates out, whilst the other bodies remain in
solution. The ammonia-compound is washed with cold alcohol, and
boiled with dilute acetic acid.
Aurin ia but sparingly soluble in water, and crystallines from
alcohol in dull-red needles with a green lustre, and from acetic acid
ia rhombic prisms, having either the colour of chromic trioxide and
a brilliant diamond lustre, or of a darker shade, showing a blue or
green reflection. It dissolves readily in alkalis, with a magenta-red
colour, and forms also with other oxides a series of very unstable
salts.
1 The name fusolic acid WAS first given to a red body existing in conl*tnr; and was
afterwards omployed to designate nil rod compounds which may bo obtained fvom
phenol by different reactions.