360 HOW CROPS PEEi). 



avidity (an insoluble double silicate being formed just as 

 in the experiments of Way, p. 343). According to Liebig, 

 a quantity of hydrated alumina equivalent to 2.696 gnns. 

 of anhydrous alumina, absorbed from a liter of solution 

 of silicate of potash containing 1.185 grra. of potash and 

 3.000 grm. of silica, fifteen per cent of the silicate. Doubt- 

 less hydrated oxide of iron would behave in a similar 

 manner. 



3. The organic acids of humus are usually the most 

 effective agents in retaining the bases when the latter are 

 in the free state, or exist as soluble carbonates or silic- 

 ates. The properties of the humates have been detailed 

 on page 230. It may be repeated here that they form 

 with the alkalies* when the latter preponderate, soluble 

 salts, but th.nt tliese cumjjounds unite readily to other 

 eartliy* and metallic* humates, forming insoluble com- 

 pounds. Lime at once forms an insoluble humate, as 

 do the metallic oxides. When, as naturally happens, the 

 organic acids are in excess, ttieir effect is in all cases to 

 render the soluble free bases or their carbonates nearly 

 insoluble. 



In some cases, ammonia, potash and soda are absorbed 

 more largely from their carbonates than from their hy- 

 drates. Thus, in some experiments male by the author, 

 a sample of Peat from the New Haven Beaver Meadow 

 Avas digested with diluted solution of ammonia for 48 

 hours, and then the excess of ammonia was distilled off 

 at a boiling heat. The peat retained 0.95° |^ of this alkali. 

 Another portion of the same peat was moistened with 

 diluted solution of carbonate of ammonia and then dried 

 at 212° until no ammoniacal smell was perceptible. This 

 sample was found to have retained 1.30" |„ of ammonia. 

 This difference was doubtless due to the fact that the 



* In the customary language of Chemistry, potash, soda, and ammonim ara 

 alkalies or alkali-bases. Lime, magnesia, and alumina are earths or earthy bases, 

 and oxide of iron and oxide of maaganese are metallic bases. 



