= 4. oe 
B.—CHEMISTRY 37 
Nearly ten years later a further series of experiments was being made 
on the catalysis of mutarotation by acids and bases (23). It was then 
observed that solutions of nitrocamphor in chloroform, to which trichlor- 
acetic acid had been added, developed an intolerable and pungent odour. 
This observation showed that the peculiar inertness of chloroform was 
due to its oxidation to carbonyl chloride or phosgene, and to the conse- 
quent elimination of traces of nitrogenous bases, in the form of inert 
carbamides (24). ‘The same series of experiments had already shown that 
some of these bases have an amazing catalytic activity. ‘Thus an accelera- 
tion of mutarotation was detected as a result of adding piperidine to 
benzene in the proportion of 1 part of the base in ro million parts of the 
solvent! This acceleration was also one of the earliest examples of a 
phenomenon which has since become very familiar, namely, a catalysis 
by bases, which could not be attributed to the presence of hydroxyl ions, 
and was therefore outside the scope of the conventional theories of 
catalysis by acids and bases, as developed and used by Ostwald and his 
colleagues. 
An immediate sequel to this discovery was the arrest in silica vessels of 
the mutarotation of solutions of nitrocamphor in benzene and in ether, to 
which traces of an anticatalyst had been added (24). Subsequent experi- 
ments showed that mutarotation could also be arrested in solutions of 
tetramethylglucose in chloroform, benzene, ethyl acetate, and pyri- 
dine (25) ; and Owen (26) developed to a fine art the process of arresting, 
almost at will and with very few failures, the mutarotation of solutions of 
tetra-acetylglucose in dry ethyl acetate. 
The climax of this work was reached when Faulkner (27) found that 
the mutarotation of tetramethylglucose could be arrested both in cresol 
and in pyridine, but proceeded too rapidly for convenient observation 
in mixtures of these two solvents. Since these mixtures gave velocities 
of mutarotation which were much greater even than in water, it was 
clear that the essential factor in promoting mutarotation was not an 
oxygenated solvent (28), nor an ionising solvent (29) (as had been suspected 
at earlier periods), nor even the zonisation of the sugar by an acid or basic 
catalyst (as most other workers had assumed), but that an amphoteric 
solvent (27) must be provided to serve as a complete catalyst for the 
process. 
PROTOTROPY. 
The migration of a hydrogen atom, in compounds such as nitrocamphor 
and the sugars, was thus shown to depend on the addition and removal of 
a proton at two opposite poles of the organic molecule. Since no satis- 
factory name had been adopted for this important group of isomeric 
changes, I proposed in 1923 to describe them by the term prototropy (30). 
The migration of a proton was, however, regarded as only a special 
example of the more general phenomenon of zonotropy (31), in which a 
radical migrates from one part of a molecule to another either as an anion 
or as a kation. 
The addition and removal of the ion from the two poles of the organic 
molecule may be either simultaneous or consecutive, but in either case 
