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CHAPTER VI.
BROWN AND BLACK COLOURING MATTERS. ASTRINGENTS.
E have now to treat of a class of proximate vegetable produ< 5 ts which
v ' are colourless by themselves, only yielding brown, grey, or black tintsunder the influence of a special oxidation, or by the adtion of peculiarmordants; most of these substances belong to a class of organic compoundsas yet not thoroughly known.
Under the common name of cutch, catechu, gambier, cashew, and terraJaponica there are met with in trade several kinds of vegetable extra&s,obtained by exhausting certain parts of plants, and evaporating the liquidthus obtained to a suitable consistency. Several varieties of this substanceare distinguished in commerce according to the country of their produ&ion, thespecies of plant they are derived from, and the form in which they are broughtinto the market. The following are the chief varieties:*—Genuine catechu,terra Japonica vera , is obtained from the internal portion of the wood of theAcacia catechu , a tree belonging to the Leguminosas, section Mimosas. Thistree, which attains a height of from 5 to 7 metres, is a native of Bengal andother parts of Hindostan, and the islands of the Indian Archipelago. In orderto obtain the catechu the tree is cut down while it is fullest of juice, the softwhite coloured splint-wood is torn and cut away, and the internal portion of thetree having been sawn into small sticks is boiled in water, in vessels made ofunglazed pottery; the liquid so obtained is concentrated first over an opencharcoal fire, and next placed for evaporation in the sun in shallow dishesuntil the desired consistence has been obtained. The extra# thus preparedyields three varieties of brown catechu, viz.:—
a. The cutch on leaves, so-called Pegu catechu , met with in the trade in
cakes, weighing from 35 to 40 kilos., packed in large leaves ; a dry,glossy, brownish-red, or blackish-brown substance, of uniform texturethroughout, and of a sp. gr. 1*39.
b. Brown cutch run into moulds, made in the sand or clay, is a less pure
and inferior article.
c. Brown catechu, in cubic-shaped cakes, packed in coarse bags, weighing
from 35 to 40 kilos, per cake; this kind of cutch is imported fromJava, Singapore, Pegu (via Calcutta), chiefly into the ports of London,Amsterdam, and Hamburg.
The Bengal cutch is obtained by a process similar to that just described,
* Guibourt, “ Journ. de Pharmacie,” (3), xi., 24, 260, 360; xii., 37,183,267. Girardin, “ Lemonsde Chimie,” 4th cditiou, ii., p. 636.