40 



The soluble ammonium humate already referred to contained, 



Nitrogen (total) 20.25% 



Nitrogen (as ammonia) 9-65.% 



calculated on a basis of dry matter. With a solution of super- 

 phosphate, this substance produced a brown flocculent precipitate. 

 Thinking that this precipitate consisted of calcium humate, 

 another portion of the ammonium humate solution was treated 

 with lime water. No precipitate was formed. Neither calcium 

 chloride or ferric chloride produced any change. On adding 

 pure orthophosphoric acid a brown precipitate was formed appar- 

 ently identical with that formed with the superphosphate solu- 

 tion. These facts indicated the formation of an organic com- 

 pound containing phosphoric acid. An attempt was made to 

 separate this compound, but it was exceedingly difficult to wash, 

 and apparently underwent partial decomposition. 



From the foregoing data it appears that insoluble humus offers 

 no resistance to the extraction of the phosphoric acid of super- 

 phosphate by water. The soluble humus appears on the other 

 hand to form an insoluble compound with phosphoric acid, and 

 thus acts as an absorbent. To what extent such absorption may 

 take place was not determined. 



(b) SOLUTION 



The solvent action of two of these humus compounds was 

 considered briefly. For this purpose precipitated tri-calcium 

 phosphate, humic acid, and soluble ammonium humate were 

 selected. The experiments were carried out as follows. 



Portions of 0.5 gram of pure precipitated tri-calcium phos- 

 phate were placed in small flasks, and to some of these was added 

 i gram of insoluble humic acid, and 10 c.c. of water. To other 

 portions were added 10 c.c. of the solution of ammonium humate. 

 The contents of the flasks were shaken occasionally for five days, 

 after which the residues were filtered off, washed with cold 

 water, and the phosphoric acid determined in the filtrate and 

 washings. 



A blank experiment was made with 0.5 gram of precipitated 

 tri-calcium phosphate and 10 c.c. of water treated as described 



