TRANSACTIONS OF THE SECTIONS. 63 



to a group of hydrocarbons whicli were first discovered among the products of the 

 destructire distiUation of coal or oil. The central body round which these 

 researches have chiefly turned is benzol, whose discovery will always be asso- 

 ciated with the name of Faraday. With this body naphthalin and anthracene form 

 a series, whose members difter by C^ H,, and their boiling-points by about 140°, 

 The recent researches of Liebermann have proved, as was before suspected, that 

 chrysene is a fourth member of the same series. I may add that ethylene, which 

 boils at about —70°, corresponds iu composition and boiling-point to a lower 

 member of the same series. Kekulti propounded some time ago with great 

 clearness the q[uestion as to whether the six atoms of hydrogen in benzol are 

 equivalent, or, on the contrary, play dissimilar parts. According to the first 

 hypothesis, there can be only one modification of the mono- and penta-derivatives 

 of benzol ; while three modifications of the bi-, tri-, and tetra-derivatives are 

 possible. On the second hypothesis, two modifications of the mono-derivatives 

 are possible, and in general a much larger number of isomeric compounds than on 

 the first hj'pothesis. Such is the problem which has of late occupied the attention 

 of some of the ablest chemists of Germany, and has led to a large number of new 

 and important investigations. The aromatic hydrocarbons, toluol, xylol, &c., 

 which diSer from one another by CHj, have been shown by Fittig to be methyl 

 derivatives of benzol. According to the first of the two hypotheses to which I 

 have referred, only one benzol and one methyl benzol (toluol) are possible, and 

 accordingly no isomeric modifications of these bodies have been discovered. But 

 the three following members of the series ought each to be capable of existing in 

 three distinct isomeric forms. The researches of Fittig had already established 

 the existence of two isomeric compounds having the formula C^ Hj„, — methyl- 

 toluol (obtained synthetically from toluol) and isoxylol (prepared by the removal 

 of an atom of methyl from the mesytelene of Kane). The same chemist has since 

 obtained the third modification, orthoxylol, by the decomposition of the paraxy- 

 lylic acid. These three isomeric hydrocarbons may be readily distinguished from 

 one another by the marked difterence in the properties of their trinitro-compounds, 

 and also by their diflerent behaviour with oxidizing agents. Other facts have been 

 adduced in support of the equality or homogeneity of position of the hydrogen 

 atoms in benzol. Thus Iliibner and Alsberg have prepared aniline, a mono- 

 derivative, from diflerent biderivatives, .and have always obtained the same body. 

 The latest researches on this subject are those of Richter. 



Baeyer has prepared artificially picoline, a base isomeric with aniline, and dis- 

 covered by Anderson iu his verj^ able researches on the pyridine series. Of the 

 two methods described by Baeyer, one is founded on an experiment of Simpson, in 

 which a new base was obtained by heating tribromallyl with an alcoholic solution 

 of ammonia. By pushing further the action of the heat, Baeyer succeeded in 

 expelling the whole of the bromine from Simpson's base in the form of hydro- 

 bromic acid, and in obtaining picoline. The same chemist has also prepared 

 artificially collidine, another base of the pyridine series. To this list of remark- 

 able synthetical discoveries, another of the highest interest has lately been added 

 by Schifl" — the preparation of artificial confine. He obtained it by the action of 

 ammonia on butyric aldehyde (C4 H^ 0). The artificial base has the same com- 

 position as coniiue prepared from hemlock. It is a liquid of an amber-yellow 

 colour, having the characteristic odour and nearly all the usual reactions of ordi- 

 nary confine. Its physiological properties, so far as they have been examined, 

 agree with those of confine from hemlock ; but the artificial base has not yet been 

 obtained in large quantity, nor perfectly pure. 



Valuable papers on alizarine have been published by Perkin and Schunck. The 

 latter has described a new acid, the antliraflavic, which is formed in the artificial 

 preparation of alizarine. Madder contains another colouring principle, purpurine, 

 which, like alizarine, yields anthracene when acted on by reducing agents, and has 

 also been prepared artificially. These colouring principles may be distinguished 

 from one another, as Stokes has shown, by their absorotion bands ; and Perkin has 

 latel}' confirmed by this optical test the interesting observation of Schunck, that 

 finished madder prints contain nothing but pure alizarine in combination with 

 the mordant employed. 



