88 



a System that van 't Hoffs law can be applied with 

 accuracy. 



Moreover even in this case a spécial factor cornes into 

 play, through which an important déviation at higher 

 températures is a priori probable. The reaction hère takes 

 place between the zymase which is enclosed within the 

 living cell and the sugar-soJution outside it. Thus the 

 transformation only takes place when the sugar diffuses 

 inwards and the reaction-products diffuse outwards in the 

 opposite direction. Xow, since at each 10° C. rise of tem- 

 pérature the velocity of diffusion only rises about 20 % ') 

 and the velocity of fermentation 150 — 200 %, it is to be 

 expected that at higher températures the velocity of 

 fermentation will remain considerably under the theoretical 

 values, in conséquence of the diffusion not proceeding 

 quickly enough. 



Finally, the possibility must be considered that also in 

 alcoholic fermentation the favourable influence of higher 

 températures first makes itself felt as a function of time, 

 in the same way as was the case in this inquiry at 

 30° C, and that the theoretical values according to 

 van 't Hoffs law hâve hère too no real existence. For 

 if it takes a certain time for the reaction-velocity to reach 

 the value belonging to that température then this value 

 will never be reached, because, before that happens the 

 harmful influence of the high température will already 

 hâve made its action felt. The values obtained for the 

 reaction-velocity at high températures will then, especially 

 after a short time of previous warming, be lower than 

 uught to be the case according to Blackman's themy. 

 The values when extrapolated for time .0 will also be 

 found too low. 



1) cf. Cohen, 1907, p. 126. 



