118 BULLETIN No. 145 [April, 



til free from barium and the phosphorus determined. This phos- 

 phorus must have been derived from organic sources. The results 

 are recorded in the last column of Table 23 and compare very well 

 with those previously obtained. 



According to Schmoeger, extraction of the soil for 24 hours 

 with 12 percent cold hydrochloric acid removes all of the inorganic 

 phosphorus readily soluble in dilute acids. Would not such treat- 

 ment also remove any inorganic phosphorus readily soluble in 

 dilute alkali? It would certainly seem that the subsequent extrac- 

 tion with dilute ammonia of the acid extracted residue ought to 

 dissolve only organic phosphorus. This idea was confirmed by ex- 

 perimental evidence and thus additional information regarding the 

 nature of the ammonia-soluble phosphorus was obtained. 



Two samples of 10 grams each of the soil under consideration 

 were extracted for 24 hours with 100 c.c of 12 percent cold hydro- 

 chloric acid, then filtered and washed with hot water until the fil- 

 trate was free from chlorides. One of the samples was then 

 extracted with 4 percent ammonia for 36 hours in the usual way 

 and the amount of ammonia-soluble phosphorus determined : the 

 second sample was again extracted with 12 percent cold hydro- 

 chloric acid for 36 hours and the amount of soluble phosphorus 

 determined. Both experiments were duplicated. The dilute am- 

 monia extracted 540 and 570 pounds of phosphorus or an average 

 of 555 pounds of phosphorus per two million pounds of soil which 

 had previously been extracted with cold 12 percent hydrochloric 

 acid, while a second extraction with cold 12 percent hydrochloric 

 acid yielded only 94 and 96 pounds or an average of 95 pounds of 

 phosphorus per two million pounds of soil. 



It would seem reasonable to suppose that both extractions of 

 the soil with cold 12 percent hydrochloric acid removed some 

 organic phosphorus since Berthelot and Andre (31) have demon- 

 strated that organic matter of the soil is somewhat soluble in this 

 reagent. 



It would also seem very unreasonable to suppose that dilute 

 ammonia possessed as great a solvent power for inorganic phos- 

 phorus as does 12 percent cold hydrochloric acid. But, assuming, 

 for the sake of argument, that only inorganic phosphorus is ex- 

 tracted by the hydrochloric acid and that dilute ammonia has as 

 great a solvent power for inorganic phosphorus as the hydrochloric 

 acid, the above experiments seem to demonstrate that at least 

 460 pounds of phosphorus (555-95) of the ammonia-soluble phos- 

 phorus has been derived from organic sources and that at least 

 83 percent of the ammonia- soluble phosphorus has been derived 

 from organic sources. 



