NITROGEN IN THE DIFFERENT LAYERS OF SOILS. 295 



Such a condition undeniably proves the origin of 

 nitrogen in the arable soil. 



If the upper layers which are constantly deprived 

 of nitrogen by cultivation, contain more of this element 

 than the lower, it necessarily follows that the nitrogen 

 must have come from without. The analysis of the 

 most various kinds of soil in many different lands and 

 districts shows that there is scarcely a single fruitful 

 wheat soil which does not contain at least 5000 to 6000 

 kilogrammes ( 98 to 118 cwt.) of nitrogen per hec- 

 tare ( = 2-J acres) to the depth of 25 centimetres (;= 10 

 inches) ; and the simplest comparison of the quantity 

 of nitrogen in the soil, with that which is removed in 

 the crops, proves that the latter amounts to a very small 

 fraction, and that the land is exhausted of all other 

 nutritive substances sooner than of nitrogen. 



The experiments of Mayer ( c Ergeb. landw. u. agric. 

 Yersuche.' Miinchen. Iter Heft, s. 129) show that the 

 behaviour of arable soil with respect to alkalies in 

 watery solution affords no conclusion as to the nature 

 of the nitrogenous compounds therein contained. It 

 had been assumed, that all nitrogen in the earth in the 

 form of ammonia could be separated by distillation 

 with caustic alkalies, and that the portion that was not 

 thus separated did not exist as such. Mayer proved 

 the incorrectness of this assumption ; he first discovered, 

 that many earths rich in humous constituents when 

 boiled for four hours (which may be considered equiva- 

 lent to lixiviation for four hours with boiling water) 

 still retained a very considerable quantity of ammonia. 

 The earths employed in these experiments were (1) earth 

 from the hollow trunk of a tree, (2) garden soil rich in 

 organic matters, from the Botanic Garden, (3) strong 

 clay soil from Bogenhausen. 



Ammonia. 



One million milligrammes ( = 2-2 Ibs.) retained at the temperature of 



boiling water : 



milligr. grs. milligr. grs. miliigr. grs. 



(1) Tree soil, 7308 = 112 (2) Garden soil, 4538 = 70 (3) Clay, 1576 = 24 



If an arable soil after saturation with ammonia, by 



