CHAPTEE YIIL 



EAKTHY 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 duration of the effect of the neutral and of the soluble phos- 

 phate (superphosphate) of lime The Saxou manuring experiments. 



THE earthy phosphates are among the most impor- 

 tant agents for restoring the impaired productive- 

 ness 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 producing 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 

 lie intends to accomplish, as some sorts will 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 

 lime the superphosphates are particularly suitable for 

 supplying the upper layer of the soil with phosphoric 

 acid. Their effect upon the produce of potatoes and 

 of cereals on such fields is equal to that of Peruvian 

 guano. For turnips and rape, which derive advantage 



