CONTENTS 



HISTORICAL 5 



Summary 20 



EXPERIMENTAL 



I. Methods of Determining Phosphoric Acid 22 



II. Relation between Phosphoric Acid and Compounds 



of Iron and Calcium 23 



(a) action of lime on ferric phosphate 24 



(b) action of lime on the phosphate formed 



by fixation 27 



(c) action of lime on soils 31 



(d) fixation of phosphoric acid in the 



presence of compounds of iron and 



calcium 34 



III. Behavior of Phosphoric Acid towards Humus 35 



(a) absorption 



(b) solution 40 



IV. Absorption of Phosphoric Acid by Zeolites 41 



V. Action of Ferrous Sulphate 44 



CONCLUSIONS 46 



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