A Manual of the Chemistry of the Carbon Compounds

CARBON COMPOUNDS. 461
Acid ia obtained by the action of nitric acid on chrysophanic acid
and on aloin (the bitter principle of aloes). It forms thin, yellow,
fern-shaped crystals, resembling lend iodide, and dissolving sparingly
in water with a purple colour. Barium chrysamaU CuI^O"2(lf02)4
O4Ba + 2H3O is obtained in red crystals by adding barium acetate
and acetic acid to a solution of the potassium salt. Lead clirysamato
CMHiiO < 'j(NO2)4CU ) b + 4H20 is produced in a similar way, by using
lead acetate, and forms crystals exhibiting a magnificent bronze
reflection.
Eydrochrysamide C^O'ISE^O^OE)-—When chrysamie acid
is boiled with a solution of potassium sulphide, it dissolves with a
deep-blue colour, and, on cooling, hydrochrysamide separates out in
crystals, having a blue colour and copper-red reflection.
Frangulic Acid CMH0O"2(0H)a occurs as glucoside, called fmngulin,
in the bark of JRIiamnws frangula; on boiling it with hydrochloric
acid, it splits up into glucose and frangulic acid, which crystallizes
from alcohol in orange-yellow needles or quadratic plates, containing
one and a-half molecules of water. It dissolves in potash with a
cherry-red colour, which disappears on boiling it with zinc-dust, but
comes baek again in contact with the air. Barium chloride gives,
with the red solution, a red precipitate.
Diacetyl-frangidk Acid CuH0O*'?(OC8H3O)2 is formed by heating
frangulic acid with acetyl chloride. It crystallizes from boiling
alcohol in small, yellow, lustrous plates, melting at 184°.
TitOXYAN-TflBAQUINONKS
Purpiirin exists in the free state, and as glucoside, in madder-root,
and may be extracted by a solution of alum, in which alizarin is insoluble.
It crystallines in yellow needles, with one molecule of
water; on heating, the water is given off, and purpurin sublimes hi
red needles. It dissolves sparingly in water, and more freely in
alcohol, with a red colour, which on adding on alkali becomes darker,
but not purple. The calcinm and barium salts are purple precipitates.
The solutions of purpurin give different absorption-spectra
(Fig. 14), which enable us not only to deteot the merest trace of purpurin
present in the midst of a quantity of impurities, but also to
distinguish it from alizarin, which gives a totally different spectrum.
Nitric acid oxidises purpurin to oxalic acid and phthalic acid.
Mitnjistin is found together with purpurin in Munject, or the
Indian madder (RvJbict Munjista). It is soluble in hot water, in
alcohol, and ether; its ethereal solution exhibits a fine fluorescence,
resembling that of a solution of quinizarin.
Munjistin crystallizes in yellow plates, and dissolves in alkalis
o a 2