ON DYNAMIC ISOMERISM. 197 
Similar observations have been made by Forster,! who found that a 
solution in chloroform of enolic a-benzoyleamphor could be ‘ preserved in 
darkness during twelve hours, exposed to bright sunlight during two 
hours and even sown with a crystal of the ketonic isomeride’ without 
undergoing change ; usually, however, six days were sufficient to bring 
about the condition of equilibrium indicated in the equation 
/PH COC Hs C.CO.C,H 
[39 %) aah oh = aE Se De at [61 %)- 
More recently it has been found possible to prepare solutions in benzene 
containing a mixture of normal and pseudo £-bromonitrocamphor which 
could be kept unchanged during several days in a graduated flask, but 
reached a condition of equilibrium in a single day when brought into 
contact with the softer glass of a polarimeter tube.? Of themselves, there- 
fore, these isomerides are as stable as, for instance, are ethyl alcohol, 
CH;.CH,.OH, and methyl ether, CH;.0.CH;, or methyl acetate, 
CH;.CO.0.CH;, and propionic acid, CH;.CH,.CO.OH; but unlike these 
latter substances they become isodynamic in presence of an almost incon- 
ceivably minute amount of impurity. The addition to a solution of 
nitrocamphor in benzene of 0:0001 per cent. of piperidine is sufficient to 
- establish equilibrium in two or three hours. 
3. An Lonising Solvent may promote Isomeric Change.—-Although in 
the cases described neither benzene nor chloroform is capable of bringing 
about isomeric change, it is possible that an ionising solvent may act as 
the necessary ‘third substance.’ The isomeric change of nitrocamphor is 
accelerated to some extent by acids as well as by alkalies, and in ionising 
solvents the change is very rapid even when purified material is used ; as 
pseudo-nitrocamphor is itself a strong acid it may well act under these 
conditions as a catalytic agent. In the case of aqueous solutions of glucose 
quantitative measurements have shown that the isomeric change cannot 
be ascribed to acid or to basic impurities, whilst neutral salts retard 
rather than accelerate the change ; the effect appears, therefore, to be 
produced directly by the solvent, assisted, perhaps, by the feebly acid 
properties of the glucose itself.? 
4. Many substances only become Isodynamic at High Temperatures cr 
in presence of a special Catalytic Agent.—Whilst it is now recognised that 
the changes which Butlerow regarded as spontaneous are actually brought 
about by a trace of acid or alkaline impurity or by an ionising solvent, 
there are many substances which, like the isodibutylenes, only become 
isodynamic under somewhat special conditions. Thus many sulphonic 
acids, like Butlerow’s olefines, become isodynamic when dissolved in con- 
centrated sulphuric acid ; again where isomeric change involves the trans- 
ference of an alkyl group, it may often happen that an alkyl iodide or an 
aluminium haloid is the only efficient agent. Apart from their great 
scientific and commercial importance these cases of dynamic isomerism are 
of interest as enabling isomerides to be directly balanced against one 
another of which the relative stability could otherwise be determined only 
indirectly from the heats of combustion. In other cases a reversible 
isomeric change appears to set in spontaneously when the temperature is 
1 Trans. 1901, 79, 999. 2 Lowry, Proc. 1903, 19, 131. 
8 Lowry, Zrans. 1903, 88, 1314. : 
