E. J. Russell and J. A. Prbscott 



101 



Table VII {continued) 

 Time = 1 hour. N/IO citric acid. 



P2O5 added (msrms. per 



1000 c.c.) ...^ 



P,05 found in solution (C) 



"(msms. per 1000 c.c.) ... 36-1 

 PoOj left in soil (y) (mgms. 



"pel' 100 gms.) 37-8 



10-5 

 4G-7 

 37-8 



210 

 550 

 421 



31-5 420 

 65-8 75-G 

 41-5 44-7 



Equation obtained : y = 13-4 C3"0 . 



Titne = 24 Jiours. N/IO citric acid. 



PjOj added (mgms. per 

 lOOOc.c.) 



P2O5 found in solution (C) 

 (mgms. per 1000 c.c.) ... 



PjOg left in soil {y) (mgms. 

 per 100 gms.) 



420 

 81-3 

 31-3 



Equation obtained : y = 4-l C2-2. 



It is thus clear that the reverse reaction, i.e. the removal of the 

 P2O5 from the solution by the soil is an ordinary adsorption, and conforms 

 to the general law expressed by the equation already given. 



Turning now to the direct reaction, this must obviously be studied 

 by eliminating the reverse reaction, which as we have seen can be done 

 by the diffusion method. The results for citric, nitric and hydro- 

 chloric acids are given in Table VIII and are remarkably alike : 

 considerably more so than when the experiment is carried out by the 

 usual extraction method. Sulphuric acid, however, brings out more 

 P2O5 than any of these. 



Reference to Table III and Fig. 3 shows that the net solvent action 

 of these three acids is very different, citric acid dissolving most, hydro- 

 chloric acid next, and nitric acid least. 



It follows, therefore, that the reverse reaction, i.e. the adsorption 

 of P2O5 from the solution is greatest in presence of nitric acid, next 

 of hydrochloric, and least in presence of citric acid. 



