134 DR ANDERSON ON THE CONSTITUTION AND PROPERTIES OF PICOLINE, 



to me that the odour of the latter substance was different from that of chloro- 

 phenesic acid, which is produced by the action of chlorine on aniline. 



The preceding investigation is sufficient to establish the identity, in constitu- 

 tion and difference, in properties of picoline and aniline. These substances are 

 then isomeric, in the strict sense of the term, possessing the same composition 

 per cent., and the same atomic weight. 



Although isomerism has been recognised in a gi-eat variety of different classes 

 of compounds, I believe the present to be the first instance in which it has been 

 satisfactorily proved among organic bases. Two instances, indeed, have been 

 previously described, but in neither can the evidence be considered absolutely 

 conclusive. One of these cases is that of two bases discovered by Pelletier and 

 CouERBE* in the husks of the Cocculus Indicus, to which they have given the 

 names of Menispermin and Paramenispermin. The characters which they have 

 assigned to these substances are sufficiently distinct, but their analyses of both 

 lead to the formula C^ Hi, N 0,. This result, however, is unsupported by any de- 

 termination of their atomic weights, without which the isomerism cannot be 

 admitted as proved. The other instance is that of bebeerine, which, according 

 to the analysis of Dr D. Maclagan,! is isomeric with morphia, both being repre- 

 sented by the formula Cj-, Hjo N 0, ; and as this result is supported by the analysis 

 of the platinum compound, the probability of their isomerism is much higher than 

 in the former case. Unfortunately, however, another source of fallacy enters 

 into the question in the amorphous condition of bebeerine, which renders it im- 

 possible to determine with certainty its freedom from impurity ; even the consti- 

 tution of morphia, by far the most definite of the two substances, can scarcely be 

 considered as fixed, Gerhardt, for instance, representing it by the formula 

 C.„; Hi, N 0,!, and not by that formerly given. 



With aniline and picoline, however, these uncertainties disappear. Both 

 substances are possessed of definite boiling-points widely different from one 

 another, and of all the other physical characters of pure substances. The low- 

 ness of their atomic weight also precludes any possibility of doubt regarding the 

 true formula, and enables us to speak with certainty as to the identity of their 

 constitution. The isomerism of these substances is, moreover, of much higher 

 interest in a theoretical point of view. Menispermin and moi-phia are isolated 

 substances, entirely unconnected, in constitution or general relations, with any 

 other substance. Aniline, on the other hand, is a member of one of the most 

 extensive, widely distributed, and interesting groups of substances, with which 

 the recent discoveries of organic chemistry have made us acquainted, the Indigo 

 Salicyl and Benzoil series. The members of this larger gi-oup already present a 

 variety of instances both of isomeric and polymeric compounds, a few of which I 



* Annales de Chiniie et de Physique, vol. liv. 



I Proceedings of the Royal Society of Edinburgh, No. 26. 



