44 



ficial preparation decreased slightly the absorptive power, indi- 

 cating the presence of a small amount of aluminum hydroxide. 



It is doubtful whether there exists in soils silicates identical 

 either with the natural or the artificial materials used in the 

 above work. But it is believed that the data here presented 

 serves to show that the zeolitic silicates in soils may take part 

 in the fixation of phosphoric acid. 



V. Action of Ferrous Sulphate 



The value of ferrous sulphate in agriculture appears to be 

 questionable. Regarding its action towards phosphoric acid, 

 two possibilities suggested themselves, namely, (i) the hydrol- 

 ysis and consequent solvent action of the sulphuric acid formed, 

 on the insoluble phosphates, ^2) the action in retaining the 

 phosphoric acid applied in a comparatively soluble form. 



The solvent effect on several phosphatic materials was deter- 

 mined by placing i gram of each in a flask and treating with 

 i gram of ferrous sulphate, 100 c.c. of water, and shaking 

 occasionally for four days. The residues were filtered, washed, 

 and the filtrate tested for phosphoric acid. None was present in 

 any case. The residues were then treated with 100 c.c. of i per 

 cent citric acid, and the solubility of the phosphoric acid in this 

 reagent determined. The following table contains the data 

 showing the effect of ferrous sulphate on the solubility in i per 

 cent citric acid. 



SOLUBILITY IN I PER CENT CITRIC ACID 



Material. No FeSO 4 . FeSO 4 



P2Oo dissolved. ?2O,5 dissolved. 



Tri-calcium phosphate 26.40% 20.40% 



Tri-calcium phosphate 26.20% 20.50% 



Ferric phosphate 12.05% II -5% 



Ferric phosphate 12.20% 11.25% 



Apatite 1-47% 1.36% 



Apatite 1.47% i-44% 



Wavellite trace trace 



Wavellite ._ trace trace 



