28 



scribed under ferric phosphate. Four others were treated with 

 0.5 gram of lime, enough water added to make a thin paste, and 

 the mixture allowed to stand one and nine days. The solubility 

 in i per cent citric acid was determined, sufficient crystallized 

 citric acid being added to correct the basicity due to lime. The 

 superphosphate solution originally added contained 0.1340 gram 

 of P 2 O 5 . Under "residues" in the following table are included 

 the amounts of P 2 O 5 absorbed : 



PaOo in 



residues. 

 0.1249 grs. 

 0.1248 grs. 

 0.1244 grs. 

 0.1240 grs. 

 0.1244 grs. 

 0.1244 grs. 



Incidentally a similar experiment was made using neatral 

 ammonium citrate solution (1.09 sp.gr.) as the solvent. For 

 various reasons this solvent was not used in the soil investiga- 

 tions. The preceding plan was followed except that the action 

 of lime was allowed to continue for two days. The results were 

 as follows : 



The results show that lime materially increased the solubility 

 of reverted phosphate of iron in i per cent citric acid. The action 

 appeared to be complete in one day. The solubility of the re- 

 verted phosphate in ammonium citrate solution was not increased 

 by the addition of lime. 



The composition of this phosphate of iron has not been deter- 

 mined. It is much more insoluble in i per cent citric acid, and am- 

 monium citrate than the normal ferric phosphate. That none of 

 the latter compound was formed in the fixation experiment, was 

 indicated by the following tests : 



