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water, the water percolating out will be found to contain only 

 traces of K 2 SO 4 , but more of CaSO 4 , MgSO 4 and Na 2 SO 4 . 

 If you use MgSO 4 , the water percolating out will be found 

 to contain little MgSO 4 but more Na 2 SO 4 , CaSO 4 and K 2 SO 4 . 

 If you use Na 2 SO 4 the filtrate will contain little Na 2 SO 4 but 

 more of MgSO 4 , CaSO 4 and K 2 SO 4 . If you use KNOs solution 

 the filtrate will be found to contain little or no KNO 3 but 

 more of Ca 2 NO 3 , Mg 2 NO 3 and NaNO 3 . In each of these 

 cases the bases supplied are retained by the soil by chemical 

 agents lurking in it, while lime, magnesia or some other base 

 is removed with the acid radicle, if any. Ammonia water not 

 containing an acid radicle, the water comes out pure, while 

 in the other cases the sulphuric or nitric acid combines with 

 the bases of the soil. 



820. Now try similar experiments with phosphate of 

 potash and silicate of potash. It will be found that both 

 phosphoric acid and potash in the one case and silicic acid and 

 potash in the other, are retained by the soil. Alkaline carbo- 

 nates are also absorbed by the soil hardly without decomposi- 

 tion. Speaking generally, chlorides, nitrates and sulphates 

 are decomposed, while silicates, carbonates and phosphates 

 are absorbed without decomposition. Soil has also the 

 power of absorbing minute quantities of chlorine, H 2 SO 4 

 and HNO 3 . In each case the absorptive power is limited, 

 i. e. } after a time the filtrate or the water percolating out of 

 the cotton wool end of the bottle will be found to contain 

 the salt poured in without decomposition or absorption. 

 Soils do not absorb all the bases with equal readiness. 

 They have the greatest absorptive power for NH 3 , then for 

 K 2 O, then for MgO, then for Na 2 O and lastly for CaO. 

 When the material for absorption is ready at hand the maxi- 

 mum degree of absorption is reached within a few hours, 

 except in the case of phosphates. When there is phos- 

 phoric acid ready for absorption the maximum degree 

 of absorption is reached after several days. Relatively 



