ON THE HYDROLYSIS OP SUGARS. 283 



rendering it temporarily inactive ; and also, in the case of volume- 

 normal solutions, displacement of water by the neutral substance. 



With regard to the first factor mentioned, it is difficult to estimate the 

 extent to which mechanical hindrance affects inversion. Reformatsky's 

 ■.nqi four experiments, showing that the catalysis proceeds as quickly 

 in a solid agar-agar jelly as in pure water, do not appear to justify 

 the importance which has been so often attached to them, whilst 

 iq(\n Levi's two experiments, showing that the presence of colloidal 

 silicic acid does not affect the inversion velocity of sugar, are 

 even less trustworthy. It seems probable, however, that the meclfcnical 

 hindrance caused by one added molecule in some fifty-five molecules of 

 solvent (a weight-normal molecular solution) would not be very great. 

 It is usually more than compensated for by the dehydrating effect of the 

 added molecules, for instance when the added molecules are glucose, 

 lactose or acetic acid. With glycerol, however, the considerations 

 numbered (1) and (3) are more potent than the dehydrating effect and 

 the result is a retardation in weight-normal solutions. 



In the case of enzymes, if the added molecules have a suitable 

 configuration and combination occurs, a considerable retardation may be 

 experienced, as acceleration by dehydration effects does not seem to come 

 into play in this case and mechanical hindrance appears to have little 

 effect. 



II 2. — Influence of Aleoliol. 



The effect of alcohol on the rate of inversion has been more studied 

 than that of any other substance ; it differs from the effect of non- 

 electrolytes in general, in that an acceleration is never observed, even in 

 volume-normal solutions. 



1 oqi Kablukow and Zacconi were the first to note that the effect of 



alcohol is to retard inversion. This retarding influence in the case 

 of some acids is much more potent than in others. 



1 9.^% Wakeman confirmed this result and also noted that the mole- 



cular conductivity of the acid is also decreased, although not 

 proportionately to the sucroclastic activity. Wakeman thought that the 

 effect of alcohol was due to an alteration in the viscosity of the solution ; 

 if this were the case the activity of all acids should be proportionately 

 diminished. 



1 RQ8 ""^^^ problem was further investigated by Cohen, who measured 



the conductivities of HCl in various strengths of alcohol over a 

 wide range of dilutions. He concluded that as the inversion velocity is 

 less in alcoholic solution, the number of hydrogen ions must be less. As 

 his conductivity measurements led him to a different conclusion, he thought 

 that perhaps the conductivity method does not give a trustworthy measure 

 of the ionisation. 



iQOQ ^^ ^b® next year Cohen showed that, even at high dilutions 



alcoholic (20 per cent, and 50 per cent.) solutions of HCl invert 

 sugar more slowly than water solutions. Hence, as the acid is 'com- 

 pletely ionised ' in the dilutions used, whether aqueous or alcoholic solu- 

 tions be used, it follows that the alcohol does not necessarily alter the 

 number of hydrogen ions but exerts a specific retarding action on the 

 invei'sion. 



•■nqr. Meanwhile Arrhenius had laid down the ruling that alcohol 



decreases the amount of the active part of the sugar. 



