no 



IMBIBITION 



1. Temperature. — The rate of imbibition increases with increase in 

 temperature (Fig. 22). Equihbrium will therefore be attained more slowly 

 at lower temperatures, but the amount of water held in an imbibant at equilib- 

 rium will be slightly greater at lower than at higher temperatures. This 

 is in accord with the principles of the influence of temperature upon adsorp- 

 tion processes generally. 



2. Osmotic Effects. — Water moves by imbibition into a substance only 

 when its diffusion pressure is in excess of the diffusion pressure of the water 



345 



TIME IN HOURS 



Fig. 22. Relation between temperature and imbibition of water by Xanthium seeds. 



Data of Shull (1920). 



in the imbibant. The introduction of a solute into water invariably has the 

 effect, as already discussed, of reducing the diffusion pressure of the water 

 in that solution as compared with pure water. The osmotic pressure of a 

 solution is a measure of its diffusion pressure deficit. Hence the magnitude 

 of the osmotic pressure of the surrounding solution would be expected to 

 influence both the rate of imbibition and the equilibrium water content of an 

 imbibant. 



One of the most comprehensive studies dealing with osmotic effects in 

 relation to imbibition has been conducted by Shull (1916) who used the 

 seeds of the cocklebur {Xanthium pe?insylvanicu/n) as the imbibing material. 

 Samples of the seeds of this species were allowed to come to equilibrium with 

 solutions of sodium chloride and lithium chloride of different osmotic pres- 



