Phenolic Solutions by Seeds of Hordeum vulgare. 129 



Table VII. 



Xime from 



Seeds in water at 19° C. 



Seeds in N/2 phenol at 19° C. 



beginning 















of experi- 



Calculated. 













ment. 



Experimental. 



Difference. 



Calculated. 



Experimental. 



Difference. 



hours. 



grm. 



grm. 





grm. 



grm. 









5 -00 



5 -00 





5 -00 



5 -00 







24 



6-03 



6 -08 



+ 0-05 



6 -64 



6-73 



+ 0-09 



48 



6-59 



6-56 



-0 03 



7 -20 



7 -22 



+ 0-02 



72 



6 93 



6-94 



+ 0-01 



7 -40 



7 38 



-0-02 



96 



7-11 



7-14 



+ 0-03 



7 -46 



7 "44 



-0-02 



(2) The Absorption Constant k, and the Interpretation of the Absorption 



Equation. 



The equation dx/dt = k (a — x) is worthy of consideration in more detail. 

 It shows that the rate of absorption of a solution by the barley at any given 

 instant is the product of two factors — the constant l\ which depends on the 

 nature of the solution, its temperature and concentration ; and the degree of 

 dryness (a — x) of the seeds. These two separate factors are considered more 

 fully below. 



(a) Effect of the Degree of Hydration of the Internal Contents of the Seeds on 

 the Absorption Sate. — The term a — x represents the difference between the 

 equilibrium weight and the weight x at any given instant. It follows there- 

 fore, from the above equation, that when the seeds are surrounded by a solution 

 of constant concentration and temperature, the rate of absorption of the 

 solution by the barley is proportional to the weight of the solution which the 

 seeds are still capable of absorbing before equilibrium is reached. For 

 convenience this weight might be termed the degree of dryness of the seeds. 

 The rate of absorption is a maximum when the seeds contain no moisture at 

 all, and zero when the seeds are full. 



The gradual falling off of the rate of absorption as the degree of fulness 

 gets greater seems to be caused by the operation of a backward pressure ;* 

 for it is evident that the solution would of itself tend to diffuse into the seeds 

 at a constant rate, since its temperature and concentration remain the same 

 throughout. But as it flows into the seeds, the gradually increasing vapour 

 pressure of the hydrated starchy contents of the seeds opposes to a 



* The existence of this backward diffusion pressure is amply proved by the fact that 

 •wet seeds gradually give up their moisture in dry air, or when immersed in anhydrous 

 alcohol, sulphuric acid, or other media to which the membrane is impermeable. The rate 

 of diffusion of the moisture outwards gets less as the seeds get drier, and finally becomes 

 zero. 



