AMMONIA RETAINED FIRMLY BY SOILS. 297 



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 am- 

 monia fixed by the soil. In this operation there is no 

 perceptible limit, where the evolution of ammonia 

 ceases ; for even after twenty-five hours of continuous 

 heating in a water-bath, the fluid which passes off has 

 still an alkaline reaction. 



The above arable soils in their natural condition 

 comport themselves with a boiling solution of soda 

 precisely as if they were partially saturated with am- 

 monia. 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 

 lime ; 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 Ibs.) from 



Havannah. Schleissheim. Bogenhausen. Clay soil, 

 milligr. grs. milligr. grs. milligr. 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 consider- 

 ations ; they show, among other things, that the third, 

 fourth, or fifth part of all the nitrogen contained in the 

 soil is separable in the form of ammonia ; and that after 

 twenty-five hours' distillation with a solution of soda, 

 the fluid which passes off has still an alkaline reaction. 



As a soil saturated with ammonia retains, after five 

 or six hours' heating with a solution of soda, a third, 

 a fourth, or a sixth of the ammonia absorbed by it, and 

 we cannot assert that the retained portion has changed 

 its nature, and is no longer ammonia ; so from the com- 

 portment of the earth in its natural condition, and under 

 the same circumstances, we cannot conclude that the 

 nitrogen which by distillation cannot be obtained in 



13* 



