426 Stiles and j0rgensen. — Studies in Permeability . V. 
A similar series of experiments with carrots showed, however, that 
a solution of sodium chloride of a concentration of about — was required to 
reduce the swelling to zero. 
%. Sucrose . 
In Fig. 7 are shown graphically the results obtained for the swelling of 
potato in solutions of cane sugar of various concentrations. It will be 
observed that the results are almost identical with those obtained with 
sodium chloride. A solution of concentration — is approximately isotonic, 
the shrinkage in this solution being almost negligible. Thus, an isotonic 
solution of sucrose has a concentration of almost double that of an isotonic 
solution of sodium chloride. This is exactly the result to be expected as 
sucrose is completely undissociated in solution, while sodium chloride is 
almost completely dissociated into its constituent ions. 
3. Ethyl alcohol . 
In the solutions of ethyl alcohol employed the general course of swell- 
ing is quite different from that obtained with sodium chloride or sucrose. 
Time in hours. 
Fig. 8. Absorption and excretion of water by potato in solutions of ethyl alcohol of various 
concentrations. 
If ethyl alcohol behaved similarly to these substances we should expect 
M 
a concentration of ethyl alcohol of about — to be isotonic, and solutions of 
higher concentration to bring about shrinkage and those of lower concentra- 
tion swelling. As a matter of fact swelling takes place at first in much 
higher concentrations than this. Thus, potato swells at first in a solution 
eight times as strong (2 M ). In this strength, however, the swelling phase 
is of short duration and reaches a low maximum after about half an hour. 
