608 



SUBSTRATE CONCENTRATION AND HYDROLYSIS 



digestion test the solution could hardly be pipetted with a wide-mouth pipette 

 and was semisolid. The figures for viscosity are doubtless all too low since the 

 viscosimeter was not known to obey Poiseuille's-^ law and almost certainly did not 

 obey it since the time of outflow for 20 cc. of water was only 10 seconds. 



The result of the experiment is shown graphically in Fig. 3. The 

 rate of digestion is not affected appreciably, until the viscosity has 

 increased four to five times that of water. This is far greater than 

 the viscosity of any solution used in the other experiments referred 

 to. There is no doubt, however, that when the solution becomes 



c 



o 



CO 



I 



17 



20 



Relative viscosity (HjO = l) 

 Fig. 3. Influence of viscosity on rate of digestion. 



nearly solid the rate of digestion is greatly decreased. It was found 

 that the same decrease was noticed if the viscosity of the solution 

 was increased by the addition of agar. The presence of the agar 

 alone is not the cause of the decrease in the rate as was shown by the 

 fact that the rate of digestion was unaffected by the agar if the experi- 

 ment was conducted at 40° (when the agar caused no increase in 

 viscosity). It would seem, therefore, that the effect of viscosity 

 must be a mechanical one due to interference with the diffusion of. 



"'' For a discussion of this question see Washburn, E. W., and Williams, G. Y., 

 /. A}n. Chcm. Soc, 1913, xxxv, 737. 



