B.—CHEMISTRY 35 
nitrocamphor, which exhibited mutarotation in a large range of an- 
hydrous solvents, but was too insoluble to be examined in aqueous 
solutions. Since interaction with the solvent was thus excluded, the 
mutarotation of nitrocamphor could only be attributed to dissociation 
or to isomeric or polymeric change. 
At that date certain sugars had already been prepared in two isomeric 
forms, which exhibited mutarotation in opposite directions (15); but 
these changes were attributed to the complete conversion of the two 
sugars into a third isomeride (16). In the case of x-bromonitrocamphor, 
however, the product of mutarotation of the normal and pseudo forms 
was obviously an equilibrium-mixture of these two substances, and not 
‘a third isomeride, since, on evaporation of the solution, crystals of the 
normal and pseudo forms were deposited side by side. Mutarotation 
was therefore attributed to the reversible isomeric change of two isomers ; 
and this interpretation was regarded as generally applicable to mutarota- 
tions in which interaction with the solvent could be excluded. 
Dynamic ISOMERISM. 
The phenomenon of reversible isomeric change had been studied, and its 
essential characteristics had been fully elucidated, twenty-two years before 
by Butlerow (17) in 1877. He had shown that two isomeric forms of the 
unsaturated hydrocarbon, isodibutylene, CsH,,, could be brought into 
equilibrium by the reversible addition of sulphuric acid, since a molecule 
of sulphuric acid could be removed from the acid sulphate in two different 
ways. Simultaneously, two zsodibutyl alcohols of the formula C,H,,0, 
in the form of their acid sulphates, were brought into equilibrium by the 
reversible elimination of sulphuric acid, since the resulting olefine could 
add on sulphuric acid in two different ways : 
CH CHOH 
erteasGi Os walang eda | +H,O | 
CH, ——— CH eg : —— 
| | | 
CMe, CMe, CMe, CMe, 
Butlerow also recognised that, although sulphuric acid was required to 
bring the isomeric olefines and alcohols into equilibrium, the introduction 
of a catalyst might not be required in other cases. In particular he 
suggested that prussic acid might be regarded as an equilibrium-mixture 
of the two acids, HCN and HNC, from which the cyanides and 1so- 
cyanides CH3.CN and CH;.NC are derived : 
CH;.CN <— HCN == HNC —> CH;.NC 
Methyl cyanide. Prussic acid. Methyl zsocyanide. 
_ Butlerow’s paper did not receive the attention that it deserved, perhaps 
ecause it was published under the too modest title ‘ On Isodibutylene.’ 
uch more interest was aroused by the publication, eight years later, by 
