191o] on Applications of Polarized Light 735 



" reducing " sugars. Many explanations were given to account for so 

 mysterious a change, but nothing in the way of proof could, as a 

 rule, be oflFered in support of these suggestions. In 18i)0, however, 

 Emil Fischer discovered that similar changes of rotatory power 

 occurred when gluconic lactone was dissolved in water and thus 

 partially hydrolysed to gluconic acid — 



C.HioO, + H.3O ;! C.Hi.O, 



Gluconic lactone Gluconic acid. 



He therefore suggested that a similar explanation might be given of 

 the mutarotation of glucose, thus — 



CeH,A + H,o :i c,H,A 



Glucose Glucose hydrate. 



Mutarotation of Nitrocamphor. 



In 1896 a happy accident led me to the discovery that very 

 marked changes of rotatory power occur in freshly-prepared solutions 

 of nitrocamphor. But, unlike the case of glucose, these changes 

 could be observed in a large range of solvents. The change varied 

 greatly in the numerical values involved, but was always in the same 

 direction — from left towards right. 



The cause of the mutarotation was not difficult to discover. It 

 could not be due to hydration, nor indeed to any direct chemical 

 action of the solvent, but must be attributed to some change of 

 structure in the molecule of the nitrocamphor itself. In view of the 

 fact that the nitro compound is able to simulate the properties of an 

 acid, giving rise to strongly dextrorotatory salts, there could be little 

 doubt that the change of rotatory power was caused by a partial 

 conversion of the nitrocamphor into its acidic form — a conversion 

 which can be rendered complete by the addition of alkali. This view 

 was immediately confirmed by the discovery of a dextrorotatory 

 anhydride, which could be prepared from nitrocamphor merely by 

 evaporating its solutions on a water-bath. 



This interconversion of isomeric compounds, which we have called 

 Dynamic Isomerism, could also be used to explain the mutarotation 

 of glucose, of which two isomeric forms are known ; but there is good 

 reason to believe that the hydrolysis suggested by Fischer is also an 

 important factor when aqueous solutions of the sugar are under 

 consideration. 



In the case of bromonitrocamphor two isomeric forms of the 

 substance can actually be isolated, thus affording direct evidence that 

 the mutarotation observed in the case of this compound is due to a 

 reversible isomeric change. 



