102 



BULLETIN No. 145 



[April, 



TABLE 5. AMOUNT o^ PHOSPHORUS IN PRECIPITATED HUMUS AND FILTRATE 



Altho the amount of dipotassium phosphate added to the 

 solution had increased, the amount of phosphorus absorbed by the 

 humus was practically constant, due to the formation of definite 

 "composes phospho-humique." 



Konig (67) found that hydrogen peroxid oxidized from 40 

 percent to 70 percent of the humus present in the soil and that 

 much more of the phosphorus was soluble in pure and carbonated 

 water after oxidation than before, due, he believed, to the destruc- 

 tion of the organic phosphorus compounds. 



Fraps (69), quite recently, made a study of the phosphorus 

 extracted from the soil by 4 percent ammonia in the usual deter- 

 mination of humus. He confirmed Pitsch's results regarding the 

 possibility of some of the ammonia-soluble phosphorus being of 

 inorganic origin. He separates the ammonia-soluble phosphorus 

 into three classes as follows: 



1. The phosphorus associated with the clay held in suspension 

 in the liquid. 



2. The phosphorus precipitated with the organic matter when 

 the solution was neutralized with an acid. 



3. The phosphorus which remained in solution after the pre- 

 cipitation of the organic matter. 



With the soils under consideration he found that 1/9 of 

 the ammonia-soluble phosphorus was in the first class, 1/3 was in 

 the second class and 5/9 was in the third class. 



The phosphorus found in the first class was assumed to be as- 

 sociated with the clay particles as iron and aluminium phosphates. 

 He concluded that the phosphorus precipitated with the organic 

 matter from the ammonical solution by the addition of acids was 

 in organic combination. The phosphorus remaining in the mother 

 liquor was assumed to be derived from the iron and aluminium 

 phosphates of the soil. 



Mooers and Hampton (77) recently proposed a method for 

 obviating the error introduced in the humus determinations by the 



