314 AMMONIA AND NITKIC ACID. 



This explains the reason why an arable soil saturated 

 with ammonia gives back only a portion after being 

 heated with soda lye for several hours ; and it is rather, 

 perhaps, the lengthened operation of water at a high 

 temperature, than the chemical attraction of the soda, 

 that gradually separates, in the form of gas, the ammonia 

 fixed by the soil. In this operation there is no percep- 

 tible limit, where the evolution of ammonia ceases ; for 

 even after twenty-five hours of continuous heating in a 

 water-bath, the fluid which passes ofi* has still an alkahne 

 reaction. 



The above arable soils in their natural condition com- 

 port themselves with a boiUng solution of soda precisely 

 as if they were partially saturated with ammonia. In the 

 following table, A expresses the total quantity of nitrogen 

 in the form of ammonia, which is obtained from various 

 soils at a red heat with soda hme ; B, the quantity of 

 ammonia which is separable from them after twelve to 

 twenty-five hours' heating with a solution of soda. 



One million milligrammes of earth ( = 1 kilo. = 2-2 lbs.) from 



Havannah Schleisslieim Bogenliaiisen Clay soil 



niilligr. grs. milligr. grs. milligi-. grs. milligr. grs, 



A . . . 2640=40-6 4880 = 75-0 4060 = 62-5 2850 = 44-0 



B . . . 510= 7-8 1270 = 19-5 850 = 12 830 = 12-7 



These numbers lead to some interesting considerations ; 

 they show, among other things, that the thuxl, fourth, or 

 fifth part of all the nitrogen contained in the soil is sepa- 

 rable in the form of ammonia ; and that after twenty-five 

 hours' distillation with a solution of soda, the fluid which 

 passes ofi" has still an alkahne reaction. 



As a soil saturated ivitJi ammonia retains, after five or 



siilpliate of ammonia ; but in an arable soil, -wliicli contains carbonate of 

 lime, tlie salt of ammonia is completely decomposed : lime takes the 

 place of tbe ammonia, the latter however does not become free, but 

 enters into some other combination, upon Avhich lime has no effect. 



