ABSOKPTIVE POWER OF SOIL FOR SILICIC ACID. 135 



ratio to the absorptive power of tliat soil ; half the 

 absorptive power corresponds to double tlie diffusibility, 

 111 a similar way potash will spread in a field during the 

 time of follow. From the spot where the potash is set 

 free from a silicate by disintegration, it wiU. diffuse itself 

 through a volume of earth so much the larger in propor- 

 tion as the absorptive power of the earth for potash is 

 smaller. 



The absorptive power of arable soil for silicic acid 

 differs just as much as for potash. 



Thus from a solution of silicate of potash, 1 cubic 

 decimetre (=61 cubic inches) of these different soils ab- 

 sorbed the following quantities of silicic acid : — 



Forest soil Hungarian Garden mould I. Bogenhauscn Garden mould n. 



Milligr. Grains Milligr. Grains Milligr. Grains Milligr. Grains Milligr. Grains 



15=0-23 2644=43-8 2425=37-3 2007=31 1085=16-7 



Wlience to express the relative diffusibihty of silicic 

 acid in these soils, we have the following proportion : — 



Hungarian Garden mould I. Bogcnhausen Garden mould II. Forest soil 



1-0 1-09 1-31 2-43 17-6 



The same quantity of silicic acid which would saturate 

 1000 cubic centimetres of Hungarian earth, would 

 furnish a maximum supply for 1311 cubic centimetres of 

 Bogenhausen loam, 2480 cubic centimetres of garden- 

 mould II., and 17,600 cubic centimetres of forest soil. 



Ammonia, in the pure state, or in the form of salts of 

 ammonia, is absorbed by arable soil just in the same way 

 as potash : one kilogramme (=2-2 lbs.) of the folio-wing 

 earths Avill absorb respectively these quantities of am- 

 monia : — 



Cuban Schleiasheim Garden mould Bogenhausen 



Milligr. Grains Milligr. Orains Milligr. Grains Milligr. Grains 



5520 = 85 3900=60 3240=49-9 2600=40 



