1910} 



CARBON, PHOSPHORUS AND NITROGEN IN SOILS 



117 



Schmoeger (39) has demonstrated that the organic phos- 

 phorus compounds of the soil are decomposed by heating under 

 pressure. It would appear probable, therefore, that the simple 

 evaporation of the ammoniacal solution on the water bath in the 

 preparation of the mailer e noire in quantity for analysis would 

 cause a decomposition of the phosphorus compounds; hence when 

 the matiere noire is redissolved and precipitated by hydrochloric 

 acid, less phosphorus would be obtained in the precipitate than 

 would be the case if the material had not been heated. This idea 

 was confirmed by experimental evidence as is shown in Table 23. 

 The precipitated matiere noire obtained from the original soil, 

 which had not been extracted with hydrochloric acid, showed 19 

 pounds of phosphorus per two million pounds of soil. A portion 

 of the ammoniacal extract o"f this soil was freed from clay by 

 Frap's method; an aliquot part of the extract was then neutralized 

 with hydrochloric acid : the precipitate obtained showed 68 pounds 

 of phosphorus per two million pounds of soil, or over three times 

 as much as did the precipitate obtained from the evaporated ma- 

 terial. 



23. PHOSPHORUS IN PRECIPITATED Matikre Noire: RESULTS E}x- 

 PRESSED AS POUNDS PER Two MILLION POUNDS OF DRY Son, 



The acid extracted soil gave similar results : the precipitated 

 matiere noire which had been subjected to heat gave only 55 

 pounds of phosphorus per two million pounds of soil, while the 

 precipitated matiere noire which had not been subjected to heat 

 gave 149 pounds or nearly three times as much. The latter result 

 was again confirmed. When the ammoniacal extract, freed from 

 clay by precipitation with ammonium sulfate, is treated with 

 barium chloride, the organic matter is quantitatively precipitated 

 as is indicated by the decolorizing of the supernatent liquid and by 

 the fact that evaporation of the filtrate and ignition of the residue 

 ^gives only a very faint charring. But unfortunately the barium 

 Vhloride also precipitates the inorganic phosphorus as barium 

 phosphate under these conditions, and when the liquid is rendered 

 acid it becomes colored, showing that organic matter as well as 

 inorganic phosphorus has been dissolved. However, the precipi- 

 tate was separated by filtration, washed with hydrochloric acid un- 



