E. J. Russell and J. A. Prescott 



79 



17. It does not appear, however, that treatment with acid affects 

 the adsorptive capacity of the soil : the curve obtained after prehminary 

 treatment of the soil with acid coincides with that for the untreated 

 soil (Fig. 6). 



Agdell Soil. 



40 



y=1^■5 cri 



X Soil previously 



extracted for 24 Mrs. 



10 



20 Q 30 40 



PoOs mgm. per 1000 c.c. of solution 



50 



60 



Fig. 6. Adsorption of P2O3 in presence of N/10 HNO3 from (a) fresh soil, (6) soil 

 previously extracted for 24 hours by N/10 HNO3. 



The change in the constants with the time appears to be determined 

 by the changes in the solution. Some soil was divided into two parts : 

 one was treated with acid which had been in contact with soil for 

 24 hours, and the other with an equivalent amount of fresh acid. The 

 adsorption curves were entirely different : that obtained with the fresh 

 acid falling below the other, and being related to it in the same manner 

 as the "Time = 0" curves are to the "Time = 24 hour" curves (Fig. 7). 



It follows that the simplest results are obtained when the time is 

 reduced to a minimum, because here the composition of the liquid has 

 suffered minimum change by interaction with the soil. 



