An interesting account has lately been given by Professor Church of a new animal pigment, containing copper, found in the feathers of the violet plantain-eater and two species of Turacus, natives respectively of the Gold Coast, the Cape, and Natal. Turacine, the name proposed for it, is noticed here only because it is the first animal or vegetable pigment, with copper as an essential element, which has been hitherto isolated. The colour is extracted by solution in an alkali, and precipitation by an acid, and is changed on long exposure to air and moisture to a green hue. As the entire plumage of a bird yields not more than three grains of pigment, turacine must be looked upon as a mere curiosity.
100. Ferrate of Baryta,
Produced by adding aqueous ferrate of potash to an excess of dilute solutions of baryta salts, has been described as carmine-coloured and permanent. We have not found it to be so—an experience which has evidently not been confined to ourselves; and we cannot help thinking that this is one of those errors which get copied from one chemical work into another, to the special confusion of students. It is but fair, however, to add that in Mr. Watts' Dictionary of Chemistry, the latest and best work of the kind, this ferrate is said to become "brick-red after washing and drying at 100100° C.," and to be only "tolerably stable."
101. Gold Reds.
Many organic substances added to gold solutions throw down either the metallic gold or the red oxide, which then unites with the organic compound more or less decomposed and forms a red precipitate. Sugar, gum, the decoctions of cochineal, gamboge, fustic, turmeric, sumach, catechu, and Brazil wood, all afford red pulverulent colours. Boiled with sugar, gold solution gives first a light and then a dark red. Whatever their merits, the excessive costliness of these preparations renders them inadmissible as pigments. At one time, indeed, a gold compound known as purple of Cassius was so employed, but this soon became obsolete on the introduction of madder purple.
102. Iodine Pink.
There may be obtained from iodine and mercury a very pretty pink colour, analogous in composition to pure scarlet. It is apt to pass into the scarlet modification, and is in other respects even less to be depended on than that variety.
103. Kermes Lake
Is an ancient pigment, perhaps the earliest of the European lakes, and so called from the Arabic Alkermes. It is sometimes spelt cermes, whence probably cermosin and crimson, and kermine and carmine. In old books it is named vermilion, in allusion to the insect, or vermes, from which it is prepared. This insect is the "coccus ilicis," which feeds upon the leaves of the prickly oak in the south of Europe. Like the "coccus cacti," it is covered with a whitish dust, and yields a tinctorial matter soluble in water and alcohol. Kermes and the lac of India doubtless afforded the lakes of the Venetians, and appear to have been used by the earliest painters in oil of the school of Van Eyck. The former, under the appellation κύρνο κόκινο, is said to be employed by the modern Greeks for dyeing their caps red.
Some old specimens of this pigment which the author obtained were in drops of a powdery texture and crimson colour, warmer than cochineal lakes, and having less body and brilliancy. They worked well, however, and withstood the action of light better than the latter, though the sun ultimately discoloured and destroyed them. In other respects, they resembled the lakes of cochineal. As a colouring matter, kermes is only about one-twelfth part as powerful as that substance.