

35 



gators, notably Deherain, Kostitcheff, and others have observed 

 that calcium carbonate reacts with ferric phosphate forming cal- 

 cium phosphate, the action taking place even in the presence of 

 an excess of ferric hydroxide. Whether this was the reverted or 

 the normal ferric phosphate was not stated. 



It occurred to the author that the presence of a relatively 

 large quantity of calcium compounds might interfere with the 

 formation of reverted phosphate of iron. A short experiment 

 was made in order to ascertain whether the presence of calcium 

 carbonate would influence the fixation of phosphoric acid by 

 ferric hydroxide. 



Tri-calcium phosphate was dissolved in water charged with 

 carbon dioxide, and 200 c.c. of the solution containing 0.0176 

 gram of P 2 O 5 were added to i gram of ferric hydroxide, with and 

 without varying quantities of calcium carbonate. The action was 

 allowed to continue for ten days, after which the mixtures were 

 filtered. The solubility of the residues in ammonium citrate solu- 

 tion was determined by adding 50 c.c. and allowing to stand 

 twenty-four hours in the cold. This residue was filtered and 

 washed with cold water. The results are contained in the fol- 

 lowing table : 



Material mixed with 0.0176 grs. P2O-,. 1*205 insoluble in 



ammonium citrate. 



I gram CaCO 3 0.0018 grs. 



i gram Fe( OH) 3 0.0145 grs. 



i gram Fe(OH) 3 plus i gram CaCO 3 0.0152 grs. 



i grain Fe(OH) 3 plus 2 grams CaCO 3 0.0147 grs. 



In the blank determination above practically all the phos- 

 phoric acid was extracted by ammonium citrate. The presence 

 of calcium carbonate (one and two grams) apparently had no 

 effect on the solubility of the compound formed by the reversion 

 of phosphoric acid. 



III. Behavior of Phosphoric Acid towards Humus 



That humus possesses the power of absorbing phosphoric 

 acid from solution has not been proven. Organic soils have been 

 known to effect solution of insoluble phosphates in some cases, 



