iVBSORPTlON OF AMMONIA BY SOIL. 141 



from a soil fully saturtited mtli ammonia, pure water will 

 extract a certain quantity of it ; just as charcoal will com- 

 pletely withdraw the colouring matter from a shglitly 

 coloured fluid, but from one more deeply coloured will ex- 

 tract a much larger quantity ; a part of which, however, 

 is but feebly combined and may be removed by water. 



In Volker's experiments, treatment with a copious 

 amount of water extracted one-half the ammonia from a 

 soil saturated therewith ; the other half was retained by 

 the earth. 



Soils wliicli contain much decaying vegetable matter 

 absorb more ammonia and retain it more firmly than soils 

 that are poorer in decaying organic substances. Even 

 assuming that two cubic decimetres of earth, instead of 

 one, are required to retain completely the amoinit of 

 ammonia indicated by the absorption number, it is clear 

 that ordinary manuring with an agent abounding in am- 

 monia, such as guano or salts of ammonia, can enrich the 

 earth with this substance only to a very inconsiderable 

 depth. 



To saturate, with ammonia, a hectare (2 J acres) of 

 Bogenhausen loam, from the surface downwards to the 

 depth of one decimetre, fully, or to half-saturate it to the 

 depth of two decimetres (7 -8 inches), would require a 

 supply of 2600 kilogrammes or 52 cwts. of pure ammonia, 

 or 200 cwts. of sulphate of ammonia. 



If 800 kilogrammes of guano, containing 10 per cent, 

 of ammonia, are appHed to a hectare of Bogenhausen soil, 

 the amount of ammonia added is 80 kilogrammes ( = 17G 

 lbs.), which is a little more than the thirtieth part of the 

 quantity required to half-saturate the soil to a depth of 

 20 centimetres. Without the plough and harrow, the quan- 

 tity of ammonia contained in the guano would not pene- 

 trate, at the furthest, deeper thanTmiUimetrcs ( = 0'27inch). 



