Page:Popular Science Monthly Volume 25.djvu/219

Rh of these reactions were made by MM. Charles Girard and De Laire. Chemists, as we have said, understand by organic radicals certain groups of atoms of carbon and hydrogen, which are capable of combining with an atom of hydrogen in the same manner as an atom of bromine, or iodine, or chlorine, or which may be substituted for an atom of one of these substances in one of its combinations. In a complex body like rosaniline, one or more atoms of hydrogen may be removed and replaced by as many atoms of the organic radical. MM. Girard and De Laire caused aniline to react upon rosaniline. Aniline is an organic base, an ammoniacal compound. In common ammonia, one atom of nitrogen is combined with three atoms of hydrogen. In aniline, one of the atoms of hydrogen is replaced by the radical phenyle. The converse is also possible, and, if phenyle is in its turn replaced by hydrogen, the ammonia should reappear. This reaction was provoked by heating fuchsine and aniline together. Rosaniline gave up an atom of hydrogen and took the radical phenyle. Aniline lost phenyle, which was replaced by hydrogen; the ammonia was disengaged, and phenyl-rosaniline was produced. It is a bright sky-blue. We can vary its color. The exchange we have just described may be effected successively for three atoms of hydrogen against three molecules of phenyle, according to the amount of aniline employed; and we shall have monophenyle, diphenyle, or triphenyle rosaniline. The first is violet-blue, the second clear-blue, and the third a blue we might call blue-light (bleu lumière), because its hue loses none of its freshness—and, in fact, gains luster—even in an artificial light.

MM. Girard and Laire's discovery was of great theoretical and practical interest, and important consequences followed it. The method was general, and permitted the substitution, in most of the organic bases, of radicals for two or three atoms of hydrogen. The same chemists succeeded in doing with the hydrochlorate of aniline as they had done with the hydrochlorate of rosaniline, and obtained diphenylated and triphenylated aniline, from which they extracted blue coloring matters; then they brought the salts of these complex bases under the review of their experiments. An iodine salt of trimethylated rosaniline gave them a magnificent green, of such fixity and luster that it might be called, like the blue which they had previously prepared, green-light (vert lumière).

The light oils of coal-tar are almost wholly composed of carburets of hydrogen; in the heavy oils bases and acids are also found with some very condensed carburets. They contain, for example, the ready-formed aniline, which it has not been found profitable to extract from them, and phenic acid, which, besides its valuable antiseptic properties, has been serviceable to the fabricants of coloring matters. In 1834 M. Runge, in preparing phenic acid, found in the residue a yellow substance, which is called coralline, or rosolic acid. In 1859 M. Jules Persoz, heating this substance with ammonia, obtained a