A Manual of the Chemistry of the Carbon Compounds

THE CARBON COMPOUNDS. 440
strongly it sublimes in brilliant red needles. It is but slightly
soluble in water, but freely in alcohol and ether.
It dissolves in ammonia with a purple colour, and in potash or
soda it yields a solution which, in transmitted light, appears bluishpurple,
and, in reflected light, pure blue. This solution gives a very
characteristic absorption spectrum (see Fig. 14, No. 4).
Ho potash . . .
Purpurin' in mi-Inn sulphide
Alizarin In pot*Jh
Jnothet . . . .
Fio. 14.
By adding barium chloride to the ammoniacal solution, a blue precipitate,
consisting of CyH^O'.JOJBa, is obtained; calcinra chloride
yields a.similar compound. Alum and stannic salts produce red
precipitates in the alkaline solution, and feme salts a blackish-violet
one.
The propfirty of alizarin to form insoluble colonred metallic compounds
is made use of in dyeing and printing. To produce maddercolours
on. calico, the desired pattern is printed on the cloth as
mordant. For pinks and reds, a solution of aluminium acetate (red
liquor), which is thickened with gam or starch, is used; and for
purples and blacks, ferrous acetato (iron-liquor) is employed, whilst a
mixture of the two salts produces brown or chocolate shades. The
mordanted cloth is next " aged," or hung up in a warm airy room,
whereby the acetic acid is expelled, and the oxides are fixed in the
fibre. The cloth is now brought into the dye-bath, consisting of
boiling water and old ground madder-root*, the alizarin is gradually
dissolved and absorbed by the oxides.
Artificial alizarin is chiefly used for " topical" printing; for this
purpose it is printed together with the mordant on the cloth, which is
then " steamed" or heated to 100°; the alizarin dissolves in the free
acetic acid, which soon volatilizes, whilst the alizarin combines with
fche oxides. The colours tlms produced are more brilliant- than thosa
obtained by dyeing with madder.
To dye "Turkey-red" on cotton, the goods are mordanted with
oxidised olive-oil and alum, and then brought into the dye-bath
containing raadder-roofc or alizarin; the colour thus produced contains
fatty acids combined with alumina and alizarin.
When an alkaline solution of alizarin is heated with tin, it becomes
yellowish-red, and contains tetroxyarUhraeene CMH8(OH)t, which is
0