PROPERTIES OF ABSORBED SUBSTANCES 299 



160. Insolubility of certain absorbed substances. 

 Although bases once absorbed may be easily displaced 

 by other bases, it is a difficult matter to dissolve them 

 from the soil with pure water. Peters treated 100 grams 

 of soil with 250 c.c. of water containing potassium 

 chloride, of which .2114 grams of K 2 were absorbed. 

 The soil was then leached with distilled water, using 

 125 c.c. of water daily for ten days. At the end of that 

 time .0875 grams of K 2 had been removed, or at the 

 rate of 28,100 parts of water to one part of K 2 dis- 

 solved from the soil. Henneberg and Stohmann found 

 that it required 10,000 parts of water to dissolve one 

 part of absorbed ammonia from the soil. 



161. Influence of size of particles. The surface 

 area of the soil-particles determines to some extent 

 the amount of substance absorbed. For this, and other 

 reasons, a fine-grained soil absorbs a greater quantity 

 of material than a coarse-grained soil. In fact, it was 

 early shown by Way that the absorption phenomenon 

 is largely a function of the silt, clay and humus of the 

 soil. 



162. Causes of absorption. A number of causes have 

 been assigned for the absorption of substances by soils, 

 and there can be no doubt that the phenomenon is not 

 due to any one process. Several distinct causes are now 

 quite generally recognized and, while others that have 

 been suggested may have a part in the result, they 

 cannot all be taken up at this time. The bexter-known 

 and more important absorption processes are the fol- 

 lowing: 



163. Zeolites. As stated on a preceding page, 



