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 great 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 
CovERBE* 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,,; H, N O,. 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. MacracGan,t is isomeric with morphia, both being repre- 
sented by the formula C;; HN O,;; 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,,; Hy N O,, 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 morphia 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 group already present a 
variety of instances both of isomeric and polymeric compounds, a few of which I 
* Annales de Chimie et de Physique, vol. liv. 
+ Proceedings of the Royal Society of Edinburgh, No. 26. 

