CHAPTER IV 



PIIOSPHATIC MANURES 



TheThosphates of Calcium — The Early Use of Bones as Manure — 

 Preparation of Bone Meal and Steamed Bone Flour — Dis- 

 solved Bones and Bone Compounds — The Discovery of 

 Mineral Phosphates, Coprolites, Phosphorite, Phosphatic 

 Guanos, Rock Phosphates — The Invention of Superphosphate, 

 Lawes and Liebig — The Manufacture of Superphosphate — 

 The Manufacture of Basic Slag — Nature of the Phosphoric 

 Acid Compounds in Basic Slag : their Solubility in Dilute 

 Acid Solutions — Basic Superphosphate — Wiborg Phosphate — 

 Welter Phosphate. 



Although the fertilising effect of bones, in common 

 with most other substances of animal origin, had been 

 known in an empirical way for a very long time, the 

 efficacy was generally put down to the oil they con- 

 tained, and it was only at the close of the eighteenth 

 century that attention became fixed on the phosphoric 

 acid. 



Lord Dundonald, in his Treatise on the Connection of 

 Agriculture with Chemistry^ published in 1795, had 

 arrived at a very sound perception of the case. When 

 treating of phosphate of lime, he writes that it " is 

 contained in animal matters, such as bone, urine, shells, 

 etc., in some sorts of limestone, and in vegetable sub- 

 stances, particularly in the gluten, or the vegeto-animal 

 part of wheat and other grain. It is a saline compound, 

 very insoluble. There is reason to believe a very 



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