A Manual of the Chemistry of the Carbon Compounds

TEE CARBON COMPOUNDS. 425.
benzene. It forms colourless crystals melting at 205°, and boiling
at about 4.00°. On oxidizing it with a solution of chromic trioxid©
in glacial acetic acid it yields paradip]tenylca>icmic or paraplm/ylbenzoic
add C0H6.C6H,,.CO!!H, crystallizing from alcohol in tufts of
needles, melting at 216°, and subliming in long needle-shaped crystals.
By heating it with lime it is resolved into otirbon dioxide and diphenyl,
and by further oxidation it is converted into terephthalia
acid.
TRIPflENYMlENZENE
Is formed by heating methyl-phenyl ketoue with phosphorus penU
oxide; this reaction is perfectly analogous to the formation of
me8itylene from dimethyl ketone:—
3CJHJ.CO.CHJ = (C8H6)SC8H3 + 3H?0
It crystallizes from ether in short prisms, melting at 167°.
INMGO-GKOUP.
Indigotin, or Indigo-blue CuHI0N2Ov occurs as glucoside, called
Indiean, C68H62N2O34 in different species of Indigo/era, growing in
India, Africa, and South America, and in Isatis tiiustoria, Pdygmmm
tinctorium and Neriwn, tinctorium. It is a brown syrup, having a
nauseous, and bitter taste. On boiling it with a dilute mineral acid,
it is resolved into a kind of sugar and indigofcin:—
CfiaH02NaOM + 4H2O = Cjfi^fi, + 6CaHwO8
Indigo is obtained by macerating the plants with water, exposing
the liquid in flat vessels to the air, and stirring it up frequently.
Fermentation soon sets in, and indigo is deposited as a blue powder.
It comes into the market in the form of cubic cakes, which* when
rubbed with a hard body, exhibit a copper-red lustre.
Iudiotin sometimes occurs iu human urine which, on standing or
by adding an acid, deposits indigotin.
Commercial indigo is a mixture of different bodies; to obtain pure
indigotin, finely powdered indigo, grape'Siigar, and strong soda-lye,
are put in a flask, which is filled with hot alcohol and corked. In the
place of grape-sugar and alcohol, ferrous sulphate, and hot water may
be used. After standing for some hours, a yellow, clear solution is
obtained, containing hydro-indigotin or indigo-white; on exposing it
to the aiv iE absorbs oxygen, and iudigotin is precipitated as a crystalline
powder.
Indigotin lias a deep-blue colour with a purple tinge; it is in-