A Manual of the Chemistry of the Carbon Compounds

462 THE CHEMISTRY OF
sugars, which are different from isoduleite. Kvtin exists in capers
and the common rue; Melin, is the colouring matter of Persian berries,
and Eobinin occurs in Bobinia pseud-acacia.
Carmwie Aeid CyB^O^ is found in cochineal and in the flowers
of Monarda didyma. It is prepared by exhausting cochineal with
boiling water, and precipitating the solution with lead acetate. The
precipitate is well washed, and decomposed by hydrogen sulphide j
on evaporating the filtrate at a low temperature, carminic acid is obtained
as an amorphous brownish-purple mass. Its salts are purple
or red; the splendid pigment "carmine" is the aluminium-compound.
When carminic acid is boiled with dilute sulphuric acid it is resolved
into a non-fermentable sugar and cavmiii-ved CjjH^Oy, which
is a weak acid, and dissolves in water with a red colour.
When heated with strong nitric acid, carminic acid yields oxalic
acid and nitrococeusie, or trinitrocresotic add C^NO^gOH -! QO S TT
+ H4O, crystallizing in large silvery plates, and forming very explosive
salts. On heating it with water to 180* it is resolved into carbon
dioxide and trinUrocresol, which is identical with that obtained from
coal tar-cresol.
By fusing carminic acid with potash it yields acetic, oxalic, and
8uccinic acids and coccinin CUHUO*, a yellow crystalline body.
Bqjkocdn CjaH10O0 is obtained by heating carminic acid (or carmine)
with sulphuric acid to 140°. It is a red crystalline powder,
which, when heated with water under pressure, is converted into
orange-ied needles, and dissolves in alkalis with a red colour. By
heating it with zinc-dust the hydrocarbon C^H is obtained, subliming
in white plates, melting at 188°, and yielding by oxidation a
yellowish-white quinone. This hydrocarbon is probably a derivative
of anthracene, having the constitution CMHg^ I .
Buficarmin OieH,8Oo has been produced by heating carmine with
water to 200°. It is a carmine-red powder, which is insoluble in
water but dissolves freely in alcohol.
Indican QuB«Ffiu occurs in all the plants yielding indigo, and
sometimes in urine, and forms a pale-brown syrupy liquid, having a
bitter taste. By the action of ferments or dilute acids it is decomposed
into indigotin, a- kind of sugar, and other products.
frangulin C^H^o is prepared by exhausting the bark of
Bhaiavm frangtda with alcohol It is a lemon-yellow crystalline
powder, which dissolves in alkalis with an intense cherry-red colour,.
and is by boiling hydrochloric acid teaolved into glucose and fcangulic
acid (page 451) :—
4 4-
Riibiamc Acid, or M-uherythrie Acid CJOHJJO,^ exists in the fresh