24 
Proceedings of the Eoyal Society of Edinburgh. [Sess. 
was dependent on the presence of hydroxyl groups (Trey, Zeitsch. phys. 
Chem., 1903, xlvi, 620). Perhaps the strongest argument in favour of 
this theory is the fact that the presence of traces of caustic alkali or 
ammonia causes extremely rapid mutarotation, the rotation becoming 
constant almost immediately (Lowry, loc. cit). 
On the other hand, the non-electrolytic nature of aqueous solutions of 
sugars would appear to militate against this hydroxyl theory. Further, 
the fact that mutarotation takes place in non-hydroxylic solvents such as 
pyridine is remarkable. Pyridine appears to have been used first by Behrend 
and Roth {Annalen, 1904, 331, 359) as a solvent for glucose. They found 
an initial rotation [a] + 138'88° which became constant after twenty- 
four hours with [a] d= -f 70'89^. Subsequently they showed the formation 
of an addition compound of glucose with pyridine, Cj 2 H 220 ;^^, C^H^N, which 
decomposed on heating or on standing over sulphuric acid (Annalen, 1910, 
377, 220). 
Similar measurements with a solution of galactose in pyridine were 
made by Heikel (Annalen, 1904, 338, 71). Subsequently Grossmann and 
Bloch (Zeitsch. Ver. dent. Znckerind., 1912, 62, 19) made comparison of 
the mutarotations of xylose, rhamnose, galactose, glucose, fructose, sucrose, 
lactose, maltose and raffinose in aqueous, pyridine, and formic acid solu- 
tions respectively. They found that mutarotation took place more slowly 
in pyridine than in water solution, but in the same direction. On the 
other hand, the direction of mutarotation in formic acid is the reverse 
of that in water solution, and mutarotation is shown by non-reducing 
sugars such as sucrose and raffinose, which do not exhibit the pheno- 
menon in water or pyridine solution. Grossmann and Bloch suppose 
that in formic acid solution the higher sugars are hydrolysed and con- 
verted into formates of the simpler sugars. It seems probable that this 
would take place in the case of all the sugars, and consequently the 
changes of rotation are due not to isodynamic change but to the formation 
of these formates. 
The experiments with pyridine as solvent suggest that the hydration 
theory of the mechanism of mutarotation is untenable. If similar results 
were obtainable with other non-aqueous solvents, some new theory must 
be forthcoming. The cryoscopic experiments of Walden on the molecular 
weight of starch, using formamide as solvent, were extended by the present 
authors to the sugars, most of which are sufficiently soluble in it to allow 
of measurements of molecular weight and of specific rotation. As it was 
of importance to know that each sugar dissolved in formamide in the mono- 
molecular state, the molecular weight was determined by the cryoscopic 
