ON THE STEREOCHEMISTRY OF NITROGEN. 193 
is capable of accounting forall the observed phenomena. There are, how- 
ever, a number of problems which still remain to be solved, notably, the 
investigation of the conditions which determine the stability of isomeric 
compounds such as the hydrindamine salts. 
Notr.—Since the above was written Wedekind and Oberheide have 
studied the question of isomerism in the paratoluidine series.!  p-tolyl- 
methyl-ethyl-allyl ammonium iodide was produced in two ways, and 
p-tolyl-methyl-allyl-benzyl ammonium iodide was produced in three ways. 
In this case the stable isomerism observed in the corresponding phenyl 
compounds does not arise, and renders this still more difficult to under- 
stand. These compounds, too, have resisted all attempts to resolve them 
into their active constituents. 
Dynamic Isomerism. By 'T. M. Lowry, D.Sc. 
[Ordered by the General Committee to be printed in extenso. | 
PAGE 
I. Introductory and Historical . : , : : . . : . 193 
Il. Lhe Nature of Dynamic Isomerism . : 2 2 7196 
Ill. Zsomeric Changes in which Two Radicles are A i nterchanged é - 200 
IV. Zsomeric Changes in which a Single Mobile Radicle is Transfer red . . 204 
V. Optical Inversion ‘ - . 3 A . 211 
VI. Chemical Properties of Dynamic Tromarides : 5 F : . 214 
VIL. Physical Properties of Dynamic Isomerides ; i : “ - 3 2G 
VIII. Reversible Polymeric Change . ° . 3 “ 5 - - . 223 
I. Introductory and Historical. 
Berzelius.—Almost simultaneously with the discovery of isomerism 
the fact was recognised that isomeric compounds were sometimes capable 
of being converted into one another: in fact Berzelius, who in 1831 had 
introduced the term isomeric to express the relationship between tartaric 
and racemic acids, found it necessary in the following year to introduce 
the term metameric in order to distinguish those isomerides which differed 
in type and were on that account easily convertible into one another.” 
Berzelius’ conception of metameric compounds is very similar to that 
which forms the subject of the present report, which deals with the phe- 
nomena of dynamic isomerism or equilibrium between isomers. 
Liebig and Wéohler.—Of the two examples quoted by Berzelius, one 
(the isomerism of stannous sulphate, SnSO,, and basic stannic sulphite, 
SnOSO,) has not been realised, and the other (the supposed isomerism 
of cyanic and cyanuric acids) has proved to be an example of reversible 
polymeric change. The conversion of ammonium cyanate into urea, 
discovered by Liebig and Wéhler in 1828, is the earliest example of the 
type pictured by Berzelius. It is of interest to note that the first organic 
synthesis was effected with the aid of the first isomeric change. 
Butlerow.—Little progress was made in the study of dynamic 
isomerism until the doctrine of valency rendered possible the modern 
development of structural chemistry. In the modern period the first and 
most important contribution to the theory of dynamic isomerism is to be 
1 Ber., 1904, 37, 2712. 
2 Full quotations are given in Professor Armstrong’s article on ‘I omerism,’ 
Morley and Muir’s edition of Watts’ Dictionary of Chemistry. 
1904, ) 
