36 



while in other cases soils containing a large amount of humus ex- 

 hibited a strong attraction for phosphoric acid. 



In studying the retentive power of humus for phosphoric 

 acid it was thought best to work with the artificial preparation, 

 thereby eliminating the possibility of the interference of any other 

 absorbing material. 



To this end humic acid was prepared from sugar according 

 to the method described by Berthelot 1 . 600 grams of sugar fur- 

 nished 100 grams of the air dry material. In one portion the 

 moisture was determined by drying to constant weight at 100 de- 

 grees C. Other portions were subjected to combustion analysis. 

 The following analysis is calculated on the basis of dry matter. 



Carbon _ 61.48% 



Hydrogen 4-74% 



Oxygen 33. 



The phosphoric acid to be absorbed was applied in the form 

 of an aqueous extract of superphosphate, thus approximating 

 conditions which obtain in actual practice. Portions of i gram 

 of the air dry humic acid were placed in a small flask, 50 c.c. of 

 a solution containing 0.1550 gram P 2 O 5 and 0.0185 gram calcium 

 added to each, and the mixtures allowed to stand one, four and 

 eight days with occasional shaking. At the end of these periods 

 the insoluble matter was filtered off and washed with cold water 

 until the wash water gave no test for phosphoric acid. The 

 quantities of phosphoric acid and calcium in the filtrate and 

 washings were then determined. Calcium was determined by 

 the volumetric permanganate method. The results are found in 

 the following table. 



No. Duration of contact. P 2 Of; soluble. Ca soluble. 



1 one day o. 1540 grs. 0.0173 grs. 



2 one day 0.1545 grs. 0.0180 grs. 



3 four days 0.1535 grs. 0.0185 grs. 



4 four days 0.1550 grs. 0.0188 grs. 



5 eight days 0.1550 grs. 0.0180 grs. 



6 eight days 0.1550 grs. 0.0177 grs. 



As is shown by the above results, neither the phosphoric 

 acid nor the calcium were retained by the insoluble humic acid. 



i Chhn. Veg. Agr., 4, 123. 



