E. J. Russell and J, A. Prescott 



107 



shaking done for 10 minutes so as to complete the hour. The adsorption 

 curves were quite different (Fig. 9). 



P2O5 added, mgrns 



P2O5 found in 1000 c.c. solution (C), r 

 P2O5 left in 100 gms. soil (//), mgms. 



42-00 



35-5 



33-5 



Equation obtained: 2/ = 16-l C5'0 . 



This compares with the experiment recorded in Table VI, Fig. 4 a, 

 where the equation obtained is 



The experiment is not wholly free from criticism because we do not 

 know exactly what other changes are produced by the acid, or how they 

 are affected by the presence of the phosphate. Against the view 

 that equilibrium is only slowly attained there seems to us to be an 

 insuperable objection. The close agreement between the experimental 

 and the calculated curves shows that a definite equilibrium is attained 

 at each time. The Time = curve, for example, indicates just as 

 typical an adsorption as the 24 hour curve. Each adsorption is different, 

 but each is complete in itself. We assume, therefore, until we have 

 stronger evidence to the contrary, that equilibrium is attained 

 instantaneously. This is also true of other cases, animal charcoal, etc. 

 The next possibility is that the adsorptive capacity of the soil 

 may have increased in consequence of the action of the acid. Consider- 

 able change does take place : e.g. quantities of silica are dissolved, and 

 it is possible that the total result of the action may be to increase the 

 adsorptive capacity of the soil. Direct experiment, however, does not 

 support this view. Some of the Agdell soil was treated for 24 hours 

 with N/10 HNOg, then filtered off, washed and dried. It was then 

 treated for Time = with IINO3, and varying quantities of sodium 

 phosphate. The results are as follows: 



P.JO5 added, mgms 



P5O5 found in solution (C), mgms. 

 P2O5 left in soil [y), mgms 



Witliout pieUminary treatment 







5-0 

 200 



11-4 

 12-7 



23-8 



22-9 

 191 



28-8 



34-3 

 27-4 

 31-9 



45-7 

 36-1 

 34-7 



Equation obtained: «/ — ll-5C3"l 



