Page:Popular Science Monthly Volume 25.djvu/220

210 red body, which he called peonine. Two years afterward, the manufacturers to whom he sold his patents put in the market a sky-blue substance, azuline, which also was a derivative of rosolic acid. The precise nature of rosolic acid has not been determined; but M. Fresenius has extracted an orange-yellow matter from it, which he calls aurine, and has devised a process for procuring it by heating phenic and sulphuric acids together, and adding oxalic acid six or seven hours afterward. It is not much used now, but is of interest as furnishing in itself blue, red, and yellow. The most important bodies derived from the heavy oils are naphthaline and anthracene, both carburets of hydrogen. Naphthaline, which is solid at ordinary temperatures, and crystallizes with great facility in thin lamellæ, is obtained simply by leaving the oils in the cold for five or six days, when it becomes solidified. The liquid is decanted off, and the crystals are pressed, to remove the included oil, into thick cakes. Naphthaline is a member of the same series as benzine, and is subject to a similar series of reactions. Reducing its nitrate, Zinin obtained an organic base analogous to aniline, naphthylamine, which is transformed by the loss of hydrogen into rosanaphthylamine. From this is obtained the hydrochlorate of rosanaphthylamine, a body analogous with fuchsine, of a beautiful rose-color, and easily crystallizable, but of a clearer rose with less of violet than fuchsine. It is dull when applied to wool, but gives very brilliant hues with silk. Dissolved in alcohol, it produces a strange and wonderful effect. The liquid turns bright red, and, under proper presentation to the light, may be seen to be traversed with phosphorescent clouds. If left to stand till the alcohol has slowly evaporated, the bottom of the vessel will be covered with beautiful green, iridescent needles. Naphthaline also furnishes some very complex compounds, whence have been derived very yellow dyes, among which Manchester yellow and Martins yellow are the best known. Experiments in substituting molecules of organic radicals for atoms of hydrogen, as has been done with rosaniline, have been made with some success, but the blues thus obtained have not the remarkable fixity and luster of the similar rosaniline products.

No discovery of coal-tar products is more extraordinary or more fruitful in its bearings than that of the extraction of alizarine, or the artificial preparation of the coloring principle of madder, the effect of which has been to work a real economical revolution, and to destroy the most profitable agricultural industry of large districts of country. The madder-root has furnished the most generally used of all dye-stuffs, and the one which constituted the basis of nearly all our colors. The substance to which it owes its peculiar virtues still performs the same functions, but, instead of being derived from the cultivated root, it is now procured by chemical synthesis from stone-coal.

Alizarine is prepared from anthracene, the second of the more important bodies which we have already spoken of as contained in the