OILS AND FATS. 377 



What the organic radicals are of which these alkaloids are 

 composed is not definitely known. "When the exact con- 

 stitution of quinine, for instance, is discovered, it will be pos- 

 sible to prepare it artificially, instead of extracting it from 

 cinchona bark. This discovery will be of immense impor- 

 tance, and will doubtless prove a fortune to the happy dis- 

 coverer. 



532. Coloring Matters. There is a great variety of these 

 in the vegetable world. A portion of them are composed 

 of C, H, O, and N, but some of them contain no N. The 

 former are called nitrogenous because they contain nitro- 

 gen, and the latter non-nitrogenous. The principal of the 

 latter class are madder, hematoxyline, which is the color- 

 ing principle in logwood, Brazil-wood, and camwood, gam- 

 boge, etc. Indigo is the most important of the nitrogenous 

 class. This is derived from the juice of several species of 

 the plants called indigofera. The indigo is not, however, 

 of a blue color in the plants, but is almost colorless. It ac- 

 quires the brilliant blue color that we see it have by a fer- 

 mentation, to which the leaves of the plants are subjected 

 in the extraction of the indigo. Blue indigo is, therefore, 

 oxidized indigo, and by depriving it of its oxygen we can 

 restore it to its colorless state. When thus deoxidized it 

 is soluble, as it is in its natural state in the plant; but by 

 exposure to the air it absorbs oxygen rapidly, and so be- 

 comes blue and insoluble. The blue litmus, so much used 

 by the chemist in testing acids and bases, is a nitrogenous 

 coloring matter which is derived from certain lichens. Al- 

 most the only coloring matter of animal origin is cochineal 

 an insect. The color from this insect is called carmine. 



533. Mordants. Some coloring matters have such an 

 affinity for the substance of cloth that they will unite inti- 

 mately and firmly with the fibres, and so make fast colors. 

 But some have not this power. In order to fix the colors 



