36 SECTIONAL ADDRESSES 
Laar (18), of a speculative paper ‘ On the possibility of several structural 
formulz for the same chemical compound.’ Laar assumed that the dual 
reactivity of certain substances, of which ethyl acetoacetate is now the 
most familiar example, might be due to the incessant wandering of a 
hydrogen atom between two alternative positions in the molecule. In 
order to make his theory more precise, he compared these internal 
migrations with the vibrations which give rise to radiation in incandescent 
gases. To this phenomenon he gave the name of tautomerism, and in 
order to emphasise the contrast with Butlerow’s phenomenon of reversible 
isomeric change, he stated categorically (19) that the substances repre- 
sented by the two alternative structural formule were ‘ not isomeric but 
identical.’ 
Since two isomeric forms of x-bromonitrocamphor had been isolated in 
the crystalline state and their slow progress towards equilibrium in 
solution had been followed by observations of mutarotation, it would 
have been absurd to describe them as identical, or, in terms of Laar’s 
definition, as tautomeric. These well-defined compounds, however, 
provided an excellent illustration of Butlerow’s phenomenon of ‘ equili- 
brium between isomers.’ I therefore ventured to describe this pheno- 
menon in very obvious terms as dynamic isomerism (20), in contrast to the 
more usual condition of static isomerism, in which each isomer preserves 
its individuality and is not in process of conversion into any other member 
of the series. A full report on ‘ Dynamic Isomerism ’ was presented to 
Section B of the British Association at Cambridge in 1904, and reports of 
a Committee on Dynamic Isomerism are included in the Transactions of 
Section B from 1905 to 1916. A series of twenty-eight papers on the 
same subject has also been published in the Journal of the Chemical Soctety. 
ARREST OF MUTAROTATION. 
Further fortuitous observations showed that the mutarotation of 
nitrocamphor is not an independent intramolecular process, but depends 
on extramolecular circumstances, since under favourable conditions it 
may be arrested more or less completely over a period of several days (21). 
This discovery (which was made more than twenty years before Kurt 
Meyer’s experiments (22) on the aseptic distillation of ethyl acetoacetate in 
alkali-free vessels of silica glass) was also the result of a fortunate accident. 
The mutarotation of a solution of nitrocamphor in chloroform had been 
followed to completion during a period of about eight days, but had been 
accompanied by some loss of solvent (and possible concentration of the 
solution) by evaporation. The remainder of the solution had been left 
in the small graduated flask in which it had been prepared, and there was 
no reason to suspect that it would behave in any respect differently from 
the sample in the polarimeter tube. It was therefore a great surprise 
when, at the end of seventeen days, on attempting to confirm the final 
reading, it was found that the residue in the flask gave a rotation almost 
identical with the initial reading recorded more than a fortnight before. 
The transfer of the solution to the polarimeter tube, however, sufficed 
to initiate the mutarotation, which then proceeded with the same velocity 
as before. 
