AMMONIA RETAIXED FIK^fLY BY SOILS. 313 



monia, or in n, confiiKHl space with ammoniacal gas, or 

 over carbonate of ammonia, is then dried and exposed in 

 thin layers in this dry state to the air for fourteen days, 

 all the ammonia not intimately combined in the soil is 

 evolved, and the same result may be produced by con- 

 stant washing with cold water. Now if soils thus satu- 

 rated, the ammonia of wliich has been accurately ascer- 

 tained, are exposed to distillation with soda lye, it is found 

 that a considerable portion of the absorbed ammonia is 

 not separable in tliis way. In the following table, A ex- 

 presses the quantity of ammonia respectively absorbed 

 by various soils at the ordinary temperature of the air ; B, 

 tlie quantity of ammonia retained by the same soils after 

 twelve to fifteen hours' action of soda lye in a water bath. 



One million milligrammes (=2-2 lbs.) of soil from 



Havannah Sclilcissheim Bogenhausen Clay soil 



milligr. grs. milligr. grs. milligr. grs. milligr. grs. 



A Ammonia . 5520 = 85 3900 = 60 3240 = 50 2600 = 40 



B „ . 920 = 14 970 = 15 990 = 15 470= 7 



Under these circumstances, it appears that the power 

 of retaining a certain portion of the absorbed ammonia 

 is very unequal ; the Havanna earth (a poor lime soil) 

 retams a sixth of the absorbed ammonia, the soil at 

 Schleissheim the fourth, that at Bogenhausen almost a 

 third.* 



* We need not be surprised at this peculiar comportment, for it merely 

 proves that part of the ammonia in the earth is contained in an entirely 

 different form from that of a salt. The salts of ammonia arc com- 

 binations of ammonium, whicli can be easily decomposed by alkalies, 

 alkaline earths, and metallic oxides, the alkali taking the place of oxide 

 of ammonium, or the ammonium being displaced by some other metal. 

 But we have no reason to believe, that the ammonia, which by physical 

 attraction is fixed in the poroixs arable soil, yields its place to another 

 body, and is separable by it, if the latter has not a stronger attraction 

 for the soil. 



Carbonate of lime, in the cold, produces scarcely any effect upon 



