REMO VAL OF LIME 7 1 



solution are poured into a beaker containing a zinc- 

 copper couple reaching above the level of the liquid. 

 The solution is acidified with dilute acetic acid and left 

 overnight in a warm place, the beaker being covered 

 with a clock-glass. The nitrate is thus reduced to 

 ammonia, which is estimated by pouring the liquid, 

 together with the washings of the couple, into a 

 distillation flask, making alkaline with caustic soda and 

 proceeding as described above under Sulphate of 

 Ammonia. 



Zinc-Copper Couple. — This is prepared by immersing 

 a few pieces of zinc foil in a dilute solution of copper 

 sulphate until they are just covered with a firm deposit 

 of precipitated copper. The " couple " thus obtained is 

 washed with distilled water and kept for use in a wide- 

 necked bottle of distilled water. 



The solutions which have been standing in contact 

 with the soil are now filtered, and the ammonia, 

 phosphoric acid, potash, and nitrate estimated in the 

 respective filtrates. The amount of each which has been 

 absorbed may thus be calculated. 



Ammonia and potash are absorbed very readily by soil, and 

 phosphoric acid is also taken up to a very large extent, but in the 

 case of the nitrates the action is very slight, and practically the 

 whole of the nitrate of soda may be washed out from the soil by 

 water. 



In the case of potash and ammonium salts the absorption is 

 largely effected by interaction with calcium compounds present 

 in the soil, calcium sulphate or chloride appearing in the drainage 

 water. This may be shown by experiment. 



49. Removal of Lime from the Soil. 



(a) If the soil used in 48 contains an appreciable 

 quantity of lime, the filtrates from treatment with 

 ammonium sulphate and potassium chloride are tested 

 for calcium. A few cubic centimetres of each are 



