550 Prof. A. J. Brown and Mr. F. P. Worley. [Aug. 9, 



brought out that the slope of the curve is almost exactly the same as that 

 of the curves representing the velocity at which water is absorbed by 

 the seeds of Hordeum. 



Expressed in other terms, the relation between the temperature and either 

 the rate of entry of water into the seeds or the vapour pressure of water may 

 be approximately expressed by the equation 

 v — ae le , 



in which v represents either the velocity of absorption of water or vapour 

 pressure, and 6 the temperature, a being a constant. 



The value of h in the case of the absorption of water by Hordeum seeds, 

 derived from the mean ratios of the velocities, is 0*069 ; in the case of the 

 vapour pressure of water, it varies slightly, having the following mean values 

 between the temperatures cited : — 



0-071 between 0° and 5° 



0-069 5 10 



0-066 10 15 



0-063 15 20 



0-061 20 25 | 



So close an agreement in the general character of an exceptional property 

 common to liquid water and its vapour is an indication that the phenomena 

 may have a common origin. In the case of an exponential increase of the 

 vapour pressure of water with rise of temperature, presumably we are 

 dealing mainly with the influence of temperature on the proportion of 

 molecules of " hy drone " (OH 2 ) 2 , and, in the light of our experiments, when 

 measures are obtained of the velocity with which the passage of water takes 

 place at varying temperatures through a differential septum under the 

 attractive influence of minute particles, we may be obtaining measures of 

 the activity of the simple molecules existing in the water. It would appear 

 that only these simple molecules are directly assimilated by the seeds or 

 transmitted by the differential septum. 



The above results appear to throw light on the cause of the high tempera- 

 ture coefficients of chemical interactions occurring in solution. In a number 

 of instances it has been shown that the rate of chemical change is approxi- 

 mately doubled by an increase of 10°. It is noteworthy that the value 

 of k calculated above for the rate of absorption of water by the seeds of 

 Hordeum corresponds almost exactly to a doubling of the rate for a rise 

 of 10°, for which the exact value of Jc would be 0-0693. It appears highly 

 probable that the velocity of chemical interactions occurring in aqueous 

 solution is mainly dependent on the activity of water as expressed by the 

 proportion of " hydrone " molecules. The importance of the part played by 



