This absorbent action is most remarkably manifested in the case of ammonia and potash, but it takes place also with magnesia and soda. With the latter, however, it is incomplete, only a half or a fourth of the soda being removed from solution, the difference depending to some extent on the acid with which it is in combination. The extent to which absorption takes place varies also with the nature of the soil, and the state of combination of the substance used. Exact experiments have hitherto been chiefly confined to ammonia, potash, and lime in the free state, and as bicarbonate; and the following table gives the results obtained by Way, with solutions containing about 1 per cent of these substances in solution:-- ----------------------------------------------------------------------------- | | Loamy | Red soil,| Pure | Subsoil | | | soil, | Berkshire.| clay. | clay, | | |Dorsetshire.| | | Somersetshire.| ------------------------|------------------------|----------|---------------| |Ammonia, caustic | 0.3438 | 0.1570 | ... | ... | | " from muriate | 0.3478 | 0.1966 | 0.2847| 0.0818 | |Potash, caustic | ... | ... | 1.050 | 2.087 | | " from nitrate | ... | ... | 0.4980| ... | |Lime, caustic | ... | ... | 1.468 | ... | | " from bicarbonate | ... | ... | 0.731 | ... | ------------------------|------------|-----------|----------|--------------- From these numbers it appears that very great differences exist in the absorbent power of different soils, the first of those experimented on being capable of taking more than twice as much ammonia as the second, and nearly four times as much as the subsoil clay. It appears also, as far as absorption goes, to be immaterial whether the ammonia is free or combined. But it is different with potash, which is absorbed from the nitrate to the extent of about O.6 per cent, and from a caustic solution of potash to double that amount. The circumstances under which absorption takes place modify, in a manner which cannot well be explained, the amount absorbed by the same soil. It is found generally to be most complete with very dilute solutions, and if a soil be agitated with a quantity of ammonia larger than it can take up, it will absorb only a certain amount of that substance, but by a further increase of the amount of ammonia a still larger quantity will be absorbed.