24 



the physical condition of soils. With regard to the action of phos- 

 phoric acid in the presence of calcium (lime and calcium carbonate) 

 and iron, the literature is somewhat contradictory. The reaction 

 to some extent appears to be a reversible one. The mass law, 

 which of late years has served to clear up many unexplained 

 phenomena, undoubtedly plays a very important part. 



It occurred to the author that the beneficial effect of lime 

 might be due, to some extent, to the chemical action of this sub- 

 stance in rendering phosphates more available to crops, and that 

 the behavior of phosphoric acid in the presence of compounds of 

 calcium and iron, might depend on the relative quantities of the 

 last two present. The experiments designed to study these 

 points are described under the following heads : 



(a) Action of lime on ferric phosphate. 



(b) " " " " the phosphate formed by fixation. 



(c) '' " " " soils. 



(d) Fixation of phosphoric acid in the presence of com- 



pounds of iron and calcium. 



(a) ACTION OF LIME ON FERRIC PHOSPHATE. 



The object of the experiment was to determine the effect of 

 lime on the availability of precipitated and natural ferric phos- 

 phates. 



The solvent selected for this purpose was the i percent citric 

 acid solution proposed by Dyer 1 , for the determination of avail- 

 able plant food in soils. This reagent is the only one of the 

 many solvents proposed for determining available plant food, that 

 has received any favor among agricultural chemists. While it is 

 still of doubtful efficiency in determining absolute availability, in 

 determining relative values, for which purpose it was used in the 

 present work, it has been of unquestioned service. Dyer pro- 

 posed this reagent as representing the average root juice acidity 

 of a large number of agricultural plants examined by him. 



Precipitated ferric phosphate was prepared by treating fer- 

 ric chloride with di-sodium phosphate. The resulting precipitate 

 was washed thoroughly with cold water and the product air 



i Jour. Chem. Soc. Trans., 1894, 115. 



