346 SOILS: properties and management 



pure minerals, as they are not true chemical combina- 

 tions. The organic matter in the soil adds another class 

 of colloidal matter ; so that, in the opinion of Van Bem- 

 melen, 1 the colloidal silicates and the colloidal humus form, 

 in various proportions, a mass of colloidal complexes that 

 control the composition of the soil solution. The col- 

 loidal condition of this material is readily decomposable 

 under variations in temperature and concentration of 

 solutions, and would doubtless be in a state of constant 

 transition in the soil. 



This conception of the soil surface would account for 

 changes in the concentration of the soil solution due to 

 the application of soluble fertilizers, and would also 

 explain the continued effect of such fertilizers on the 

 theory that they are absorbed by the colloidal complexes 

 and redissolved as the soil solution tends to become more 

 dilute. 



A somewhat different view has been taken by Whitney 

 and Cameron, who hold that the composition and con- 

 centration of the solution in all soils is practically the 

 same. Their conception, according to a recent paper by 

 Cameron, 2 appears to differ from that of Van Bemmelen 

 in assuming that the soil water is in contact with the soil 

 particles for such a short time that the quantity of matter 

 that goes into solution is too slight to bear any relation 

 to the total quantity of soluble matter in the soil. The 

 soil solution does not come into equilibrium with the 

 soil mass, nor even approximate such a condition. The 



1 Van Bemmelen, J. M. Die Zusammensetzung der Acker- 

 erde. Landw. Vers. Stat., Band 37, Seite 347-373. 1890. 



2 Cameron, F. K. Concentration of the Soil Solution. 

 Original Communications, Eighth International Congress of 

 Applied Chem., Vol. 15, pp. 43-48. 1912. 



