CARBON, PHOSPHORUS AND NITROGEN IN SOILS 113 



removal of the suspended clay. Unless otherwise stated the latter 

 method was used for the removal of the suspended clay in all the 

 work reported in this paper. 



Owing- to the conflicting evidence regarding the phosphorus as- 

 sociated with the extracted matiere noire, it seemed desirable to do 

 some work with this material other than the simple determination 

 of the phosphorus. 



The soil, without previous treatment with hydrochloric acid to 

 remove the calcium, was extracted with 4 percent ammonia in the 

 ratio of i part of soil to 50 parts of ammonia water for 36 hours 

 as in the usual humus determinations. The clay was removed by 

 evaporation and the matiere noire was obtained in quantity for 

 study. Conditions here are such that the maximum quantity of in- 

 organic phosphorus should *be found in the ammoniacal extract 

 since none has previously been removed by treatment with a min- 

 eral acid as in the usual humus determinations. 



The suspended clay removed by evaporation was analyzed for 

 carbon and phosphorus with results as follows : Carbon 3.73 per- 

 cent and 3.61 percent, or an average of 3.67 per cent; phosphorus 

 0.118 percent and 0.109 percent, or an average of 0.113 percent. 

 Since the carbon in the original soil was only 2.09 percent while 

 the phosphorus was .046 percent, the relative increase of carbon 

 and phosphorus in the suspended clay indicates undoubtedly the 

 accumulation of organic matter with the "clay." It would appear 

 probable that the grinding of the sample of soil, while preparing 

 it for analysis, would convert the organic matter into an im- 

 palpable powder which would have a tendency to remain sus- 

 pended in the liquid tog-ether with the fine clay particles when the 

 soil was extracted with ammonia, 



The amount of the extracted matiere noire was determined. 

 It was then analyzed for carbon, nitrogen, and phosphorus. The 

 carbon was determined by the method suggested by Pettit and 

 Schaub (59). The total nitrogen was determined by the regular 

 Kjeldahl method ; correction was then made for the absorbed am- 

 moniacal nitrogen by determining the latter in a separate sample 

 by distillation with magnesium oxide. The phosphorus was de- 

 termined by igniting a sample of the matiere noire and treating 

 the ash with aqua regia; the silica was removed by evaporation 

 and the phosphorus determined by the usual volumetric method. A 

 confirmatory test made by determining phosphorus by fusion with 

 sodium peroxid gave 0.835 percent and 0.815 percent phosphorus 

 in the matiere noire while the method adopted gave 0.860 percent 

 and 0.830 percent. 



The results obtained expressed as pounds per two million 

 pounds of soil are recorded in Table 17. 



