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CHAPTER VIII. 



EARTHY PHOSPHATES. 



High agricultural value of phosphates — Phosphates of commerce ; selection 

 of the kind to be used dependent on the object in view, and on the nature 

 of the soil — The rapidity and the duration of the effect of the neutral 

 and of the soluble phosphate (superphosphate) of lime — The Saxon 

 manuring experiments. 



THE earthy phosphates are among the most important 

 agents for restoring the impaired productiveness of 

 land ; not that they influence vegetation in a more marked 

 manner than other mineral elements, but because the 

 system of cultivation pursued by the corn and flesh pro- 

 ducing farmer tends to remove them from the soil in 

 larger proportion than other constituents. 



In choosing among the phosphates of commerce, the 

 farmer should always keep in view the object which he 

 intends to accomphsh, as some sorts wiU answer better 

 for certain purposes than others. 



The so-called superphosphates are commonly phos- 

 phates to which a certain quantity of sulphuric acid 

 has been added, to convert the insoluble neutral lime 

 salt into a soluble acid salt. When mixed with a salt 

 of ammonia and a salt of potash, they are often called 

 guano or ammoniacal superphosphates. A good super- 

 phosphate generally contains from 10 to 12 per cent, of 

 soluble phosphoric acid. On land poor in clay and hme 

 the superphosphates are particularly suitable for supply- 

 ing the upper layer of the soil with phosphoric acid. 



