CARBON, PHOSPHORUS AND NITROGEN IN SOILS 



115 



Of the total matter e noire obtained, only 32.7 percent has been 

 precipitated from the alkaline solution by hydrochloric acid. The 

 portion remaining in solution does not consist of inorganic salts, 

 as might be supposed, as is readily shown by the fact that only 

 39.4 percent of the carbon and 37.3 percent of the nitrogen has 

 been precipitated. This shows conclusively that only about 1/3 of 

 the dissolved organic matter has been precipitated. 



Only 8.0 percent of the total soluble phosphorus, or 19 pounds 

 out of 238 pounds, has been precipitated from alkaline solution by 

 hydrochloric acid. Has the phosphorus remaining in solution in 

 the mother liquor been derived from organic or inorganic sources? 

 The fact that 60.6 percent of the carbon and 62.7 percent of the 

 nitrogen also remain dissolved in the mother liquor would appear 

 to be significant. 



Having made a study of the matiere noire obtained from the 

 original soil it seemed desirable to investigate the matiere noire 

 obtained in the usual way after the soil had been extracted with 

 i percent hydrochloric acid to remove the calcium and magnesium. 

 It seemed reasonable to suppose that the acid extraction would re- 

 move also a considerable quantity, if not all, of the inorganic phos- 

 phorus, which may have previously passed into the ammonia so- 

 lution. 



As before, the amount of matiere noire was determined and 

 then extracted in quantity for the determination of carbon, nitrogen 

 and phosphorus. The results obtained will be found in Table 20. 



TABLE 20. Mati&re Noire, CARBON, NITROGEN AND PHOSPHORUS IN THE 

 Matiere Noire: RESUI/TS EXPRESSED AS POUNDS PER Two 



MILLION POUNDS OF DRY Soil, 

 (Soil acid extracted before treatment with ammonia) 



Phosphorus-nitrogen ratio I 15.5 

 Nitrogen-carbon ratio = 1 19.1 

 Phosphorus-carbon ratio = 1 150 



The matiere noire was redissolved in dilute ammonia and an 

 excess of i percent hydrochloric acid added. The amount of the 

 precipitate and the carbon, nitrogen and phosphorus in the precipi- 

 tate were determined as before. The results obtained are recorded 

 in Table 21. 



