300 THE PRINCIPLES OF SOIL MANAGEMENT 



Way demonstrated that sand had little absorbing power 

 as compared with clay, and further, that when the 

 zoelitic silicates were removed from clay by digestion 

 with hydrochloric acid, the clay largely lost its power 

 of absorption. Way produced an artificial hydrated 

 silicate of alumina and soda, and Eichorn found natural 

 hydrated silicates or zeolites that removed bases with 

 the substitution of other bases, in the manner of natural 

 soil. A further characteristic of these zeolites is that 

 the replaced base is present in the filtrate in amounts 

 chemically equivalent to the base removed. 



It has further been shown that the absorptive power 

 of soils is more or less proportional to the amount of 

 acid soluble silicates it contains. The zeolites being 

 rather easily soluble in strong mineral acids, it is held 

 that the bases so combined are more readily available 

 to plants than in most combinations found in the soil, 

 and yet are not readily leached out of it. 



Soluble bases added to the soil in manures are taken 

 up and held by zeolites, instead of being removed in the 

 drainage water. However, nitric acid, important as it 

 is to agriculture, is not absorbed, and, together with the 

 sulfuric and hydrochloric acid, is quickly but not com- 

 pletely removed from the soil by drainage water. 



164. Other absorbents. Humus, ferric and alumi- 

 num hydrates, and calcium carbonate, exercise absor- 

 bent properties, but to what extent and of what import- 

 -ance it is difficult to say. Soils rich in humus, without 

 doubt, owe much of their fertility to the retention by 

 that constituent of a large supply of readily available 

 plant-food material. Many prairie soils that have been 



