156 



SOIL CONDITIONS AND PLANT GRO WTH 



between soil and ammonium sulphate, and Hall and Giming- 

 ham (120^), dealing with the same reaction, showed that the 

 ordinary formula for chemical equilibrium held over a limited 

 range of concentrations ; but Cameron and Patten (65^, see 

 also 300) found that it did not hold over a wider range- 

 The absorption of potassium could not be fitted at all by the 

 formula. 



When, however, the adsorption formula is used a complete 

 fit can be obtained : Wiegner (308) has gone over the re- 

 corded data and shown that they all fit the equation given on 

 page 149, viz., 



m 



the constants having the values given in Table XLIII. The 

 constants vary with changes in experimental conditions, and 

 they are by no means absolute quantities. But for a given 

 set of conditions they remain unchanged. 



Table XLIII. — Value of " Constants " Obtained in Adsorptions by 

 Soil. Wiegner (308). 



We still, however, have to account for the fact that the 

 absorbed bases displace an equivalent amount of some other 

 bases from the soil — a procedure which would be wholly un- 

 necessary if nothing but adsorption were involved. This is 

 done by supposing that only the hydroxide is absorbed : the 

 acid radicle in general is not : it therefore dissolves out some 

 of the bases from the soil. As this is a purely chemical re- 



