COAL AND THE COAL-TAR COLORS. 209 



tion of these reactions were made by MM. Charles Girard and De 

 Laire. Chemists, as we have said, understand by organic radicals cer- 

 tain 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 pheuyle 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 dis- 

 engaged, 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 amoimt of aniline employed ; 

 and we shall have monophenyle, diphenyle, or trij^henyle rosaniline. 

 The first is violet-blue, the second clear-blue, and the third a blue we 

 might call blue-light {bleu lumiere), 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 diphe- 

 nylated 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 pre- 

 pared, green-light {vert hwtidre). 



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 proper- 

 ties, has been serviceable to the fabricants of coloring matters. In 

 1834 M. Runge, in preparing phenic acid, found in the residue a yel- 

 low substance, which is called coralline, or rosolic acid. In 1859 M. 

 Jules Persoz, heating this substance with ammonia, obtained a beau- 



VOL. XXT. — 14 



