134 



CHAPTER VIL 



EARTHY PHOSPHATES AND LIME. 



The importance of phosphoric acid as the predominating 

 mineral constituent of the seed. Bones are the principal 

 source of phosphoric acid, Their composition. Bonea 

 the chief necessity of high agriculture. Their behaviour 

 to pure water, and to water containing carbonic acid. 

 Their comparative solubility depends upon their state of 

 division. The solvent action of carbonic acid upon bone 

 phosphates in solutions of common salts, saltpetre, and 

 ammonia. Superphosphate of lime. Coprolites Phos- 

 phoric acid, the chief loss sustained by the soil of India. 

 Its application to the soil will double the outturn. The 

 use of phosphoric acid in Cheshire. The action of super- 

 phosphate is immediate, and chiefly confined to the upper 

 layers. Bone-dust, on the contrary, penetrates deeper, and 

 requires some years before the maximum result is obtain- 

 ed. Mr. Robertson's experiments with bone-dust. Soils 

 most profited by bone-manure. The action of phosphates 

 on soil and plant. Quantity used per acre. 



Lime. Its extensive use as a manure. Its composition. 

 Kunkur. Quicklime. Action of lime on clay and soils in 

 general. The liberation of alkaline silicates from their 

 unassimilable compounds. Lime a powerful aid to the 

 mechanical operations of agriculture. Shell-sand. Its 

 extensive use in Ireland and France. Quantity used per 

 acre. Lime increases the assimilable store of inorganic 

 plant- food, resulting in a corresponding increase of the 

 outturn. Its use must go hand in hand with a careful 

 restoration to the soil of what is withdrawn. If not, lime 

 will enrich the father and impoverish the son. Experiments 

 of lime-manuring at Oberbobritzsch. Mr. Robertson's 

 experiments on the Madras Model Farm. Quicklime has 



