230 SCIENCE PROGRESS 



of a minute trace of an acid may in some instances prove 

 almost as efficient in arresting change as the ideal condition 

 of absolute purification ; usually, however, the presence of 

 the acid is itself sufficient to cause an interconversion of the 

 isomerides, and this simple method of demonstrating the necessity 

 of a catalyst is therefore not capable of general application. 



Glucose— In the case of the sugars, which are very sensitive 

 to the action of alkalis and only slightly sensitive to the action 

 of acids, it is possible by quantitative experiments to determine 

 the part played by these agents in promoting isomeric change. 

 The method of investigation depends on the fact that neutral 

 salts, even at very high concentrations, have no marked catalytic 

 action on the isomeric change of glucose ; it should therefore 

 be possible by careful neutralisation to get rid of any free acid 

 or alkali present in the solution, and so to check, or even 

 actually to arrest, the change. In order to account for the 

 velocity of change observed in a 5 per cent, solution of glucose, 

 it would be necessary to assume the presence of acid or alkali 

 equivalent to N/100 HC1 or N/10,000 KOH, the latter being a 

 possible figure, the former obviously out of the question. After 

 adding to an aqueous solution of glucose a quantity of hydro- 

 chloric acid sufficient to give a concentration of N/ 10,000, three 

 points on the curve which showed the velocity of isomeric 

 change were found to be absolutely normal, whilst two later 

 readings indicated a very slight retardation. The quantity of 

 acid used was a hundred times too small to produce any marked 

 acceleration, but was amply sufficient to " hold up " the change, 

 if this had indeed been due to alkaline impurities. Actually, 

 even when ten times this concentration of acid was used, no 

 substantial retardation could be effected, and the only two 

 readings which gave any indication whatever of a decreased 

 velocity showed nothing more than that 5 per cent, of the 

 observed minimum velocity might have been due to an alkaline 

 impurity present at a concentration of about N/200,000. 1 



There can therefore be little doubt that in this case the water 

 is able to bring about an isomeric change without the help of 

 acid or basic impurities; it is, however, probable that, as in 

 Baker's experiments, the water used must be sufficiently impure 

 to possess conducting properties. As the solutions used in the 

 experiments had a conductivity (mainly due to the glucose) one 



1 Lowry, Trans. Chem. Soc. 1903, 83, 1320. 



