Chica Red, Curucuru, Carajuru.—The colouring matter known under these names rarely comes into commerce; it forms brownish-red masses which acquire a peculiar golden glitter on rubbing. It is obtained from the leaves of Bignonia chica, a native of tropical America. The leaves are superficially dried and then covered with water; in the warm climate the macerated leaves soon ferment, and a deep red powder separates at the bottom of the vessel: this is the colouring matter; it is dried, made into small cakes and brought into the market.
Chica red is only partially soluble in strong alcohol, the residue chiefly consists of plant cells. Alum and stannous chloride precipitate beautiful red lakes from the solution, which are distinguished by great permanence when exposed to light. On account of the present high price, this colouring matter has not yet obtained admission into the colour industries, though it would be a valuable recruit.
Chica red has been little studied; an investigation would certainly considerably increase our knowledge of the organic colouring matters. Towards reducing agents it behaves in a similar manner to indigo; in contact with caustic soda, grape sugar and water in closed flasks, a violet liquid is produced; when exposed in an open vessel the violet at once changes to brown, but if the liquid is syphoned off into dilute hydrochloric acid a pure red precipitate separates, which is to be regarded as the pure colouring matter.
CHAPTER LVII.
LICHEN COLOURING MATTERS.
Many lichens contain compounds from which colouring matters can be obtained by appropriate treatment; the colouring matters known as cudbear, archil and litmus were formerly much more extensively used in dyeing than at present: like so many natural colouring matters they have been replaced by coal-tar dyes.
The lichens which produce colouring matters live upon trees and rocks, chiefly on the sea-shore; the colouring matters are thus generally manufactured in places near the coast. The species principally used for this purpose are Lecanora, Rocella and Usnea.
The lichens contain colourless compounds, which by treatment with acid or alkalis produce orcinol. In contact with moist air and ammonia, orcinol is decomposed into water and orcein, which is the colouring matter. The lichens are treated so as to produce the largest quantity of orcinol, which is then converted into orcein. There is not space here to enumerate and describe the many compounds obtained from lichens, only the most important can be mentioned; these are erythric, lecanoric and usnic acids. Lecanoric acid produces, under certain conditions, orsellic acid, which is again changed to orcinol.
Pure orcinol, C₇H₈O₂. H₂O, is a crystalline substance of sweet taste; it is soluble in ether, alcohol, water, etc. In damp air containing ammonia, orcinol gradually acquires a fine red colour, being converted into orcein, C₇H₇NO₃, according to the following reaction:—
C₇H₈O₂ + NH₃ + 3O = C₇H₇NO₃ + 2H₂O.
When pure, orcein is a brownish-red amorphous powder, soluble in alcohol to a scarlet solution and in alkalis to a purple solution. On the addition of water to the ammoniacal solution or of salt to the alkaline solution, orcein is again separated; this procedure may be used to completely purify the colouring matter.