336 HOAV CR0P6 FEED. 



are no longer a solution of nitrate of potash, but one of 

 nitrates of lime, magnesia, and soda. The potash has 

 disappeared from sohition* and become a constituent of 

 the soil, while other bases, chiefly lime, have been dis- 

 placed from the soil, and now exist in the solution with 

 the nitric acid. 



If we operate in a similar manner on a fresh tube 

 of soil with solution of salt (chloride of sodium), we 

 shall find by chemical examination that the soda of the 

 salt is absorbed by the soil, while the chlorine passes 

 through in combination with lime, magnesia, and potash. 

 In case of sulphate of magnesia, magnesia is retained, and 

 sul])hates of lime, etc., pass through. With jihospliatcs 

 and silicates we find that not only the ba'^e, but also these 

 acids are retained. 



Law of Absorption and Displacement. — From a great 

 number of experiments made by AYay, Liebig, Brustlein, 

 Henneberg andStohmann, Rautenberg, Pcteis, Weinhold, 

 Ktillenberg, Ileiden, Knop, and others, it is established 

 as a general fact that all cultivable soils are able to de- 

 compose salts of the alkalies and alkali earths in a state 

 of solution, in such a manner as to retain the base together 

 with phosj^horic and silicic acids, while chlorine, nitric 

 acid, and sulphuric acid, remained dissolved, in union with 

 some other base or bases besides the one with which they 

 were originally combined. The absorptive power of the 

 soil is, however, limited. After it has removed a certain 

 quantity of potash, etc., from solution its action ceases, it 

 has become saturated, and can take up no more. If, 

 therefore, a large bulk of solution be filtered through a 

 small volume of earth, the liquid, after a time, passes 

 through unaltered. 



* The absence of pofasli may be s^hown by aid of strong, cold solution of 

 tartaric acid, which will precipitate bitartrate of jxitasli (cream of tartar) from 

 the ori^'inal solution, if not too dilute, but not from that which lias filtered 

 through the soil. Tlie prcs.ence of lime in tlie liquid that passes the soil may ba 

 shown by adding to it either carbonate or oxalate of ammonia. 



