394

DYEING AND CALICO PRINTING.

crystals of lutein are apparently rhombic plates, of which two or more arealways superposed in a curious manner. The crystals are microscopic, yellowwhen thin, orange to red when thick, and have no resemblance to any otherknown animal or vegetable substance. Lutein combines with few substances,mercury-acetate being, perhaps, the only reagent by which it is immediatelyand completely precipitated as a yellow deposit; mercury-nitrate produces ayellow precipitate which, on standing, becomes white. Nitric acid pouredover the crystals produces a blue colour, which immediately passes intoyellow. The blue is not produced when nitric acid is added to either thealcoholic, ethereal, or chloroformic solution of lutein, but appears withthe acetic acid solution, and disappears again rapidly. Lutein has greataffinity for fatty matters and for albumen.

In order to prove further the wide distribution of yellow colours, we quotethe names of those vegetable substances which contain a yellow colour insufficient quantity to make them applicable as dye-wares; these are:—Quercitron bark (from the Quercus tinctoria); true or old fustic (Morus tinctoria ,or Broussonetia tinctoria; young fustic, the wood of the Rhus cotinus ; thebark, twigs, and berries of the dyer’s buckthorn, obtained from various speciesof the Rhammis, as for instance, frangula , cathartica, saxatilis , infectoria ,oleoides; the Chinese yellow, Gardenia grandijlora; saffron, Crocus sativus;safflower, Carthamus tinctoria , the fruit and leaves of the Bixa orellana (theannatto plant); rhubarb root; wall lichens, Parmelia parietina; weld, theReseda luteola , entire plant; the root of the Berberis vulgaris ; turmeric root(Curcuma tinctoria); the aloe juice; and, lastly, a host of yellow-colouredflowers, some roots, among them the Eschscholtzia, the common carrot, andthe mulberry-tree root, and also the shells of various nuts and other vegetableproducts.

Viewed as a pure immediate principle the yellow pigment obtained fromthese several plants does not prove to be identical in composition ; but itshould not be thought, on the other hand, that every species of plant containsa peculiar corresponding colouring matter. It has been proved that many ofthe yellow pigments obtained from the plants above named are very similar toeach other as far as their chemical chara<5ter is concerned, though theirphysical properties may differ widely. The yellow colouring matters metwith in quercitron bark, Persian berries, fustic, young fustic, weld, and someother plants, are very similar both in their chemical and physical chara&ers;as a result thereof the mode of their pra&ical application and fixation ontextile fibres closely corresponds, and the only difference in the shade of thecolours produced is the greater or less brightness, a tone verging more orless towards the orange, and the degree of fastness. It will thus render ourtask easier, both as regards the chemical history of the yellow pigments, andthe mode of their application on the large scale, if we include these under thehead quercitron yellows.

These yellows as met with in plants are frequently soluble, crystallisableglucosides, which on being boiled with dilute mineral acids are split up intoglucose or some analogous substance, and a new body, generally of a deepercolour, and less soluble in water, but very readily so in alcohol, and alsocrystallisable. This derivative, which while combined with the glucosicmolecule is to be considered as the real cause of the colour of the pigment,