27 



phoric acid in the proportion in which they existed in the 

 original compound. This action of potassium oxalate was made 

 the basis of a qualitative test for the presence of ferric phosphate, 

 in the presence of ferric hydroxide. The solution was found to 

 have no solvent action on ferric hydroxide. The compound 

 formed with ferric phosphate appeared to be a double oxalate, 

 very soluble in water. 



Ferric phosphate was treated with varying quantities of 

 lime. The products of the reaction were treated with the solu- 

 tion of potassium oxalate, filtered, and the filtrate tested for 

 iron. The absence of iron in the oxalate solution was taken as 

 showing the absence of ferric phosphate in the mixture treated 

 with this solvent. 0.2 gram lime was found to be the smallest 

 amount capable of completely converting i gram of ferric phos- 

 phate. 



The behavior of potassium oxalate suggested the use of this 

 reagent for determining the available phosphoric acid in phos- 

 phatic materials. A few preliminary trials on its solvent action 

 on calcium and iron phosphates, under different conditions, were 

 made. The results were not sufficiently satisfactory to indicate 

 the usefulness of this reagent. 



(b) ACTION OF LIME ON THE PHOSPHATE FORMED BY FIXATION. 



It is fairly well established that soluble phosphates when 

 applied to soils tend to pass into comparatively insoluble forms. 

 This reversion is caused largely by hydrated oxide of iron. It 

 was considered important therefore, to know the effect of lime on 

 the compound thus formed. 



To this end two grams of pure ferric hydroxide were treated 

 in a small flask with 50 c.c. of an aqueous solution of superphos- 

 phate, shaken, and allowed to stand ten days with occasional 

 agitation. The insoluble residue was then filtered off and washed 

 with cold water until phosphoric acid ceased to be given up. 

 The filtrate and washings were then analyzed and the phos- 

 phoric acid absorbed calculated. Several residues were obtained 

 in this way. Two of these were treated with 100 c.c. of i per 

 cent citric acid solution, and the solubility determined as de- 



