CARBON, PHOSPHORUS AND NITROGEN IN SOILS 119 



(c) ORGANIC PHOSPHORUS BY SCHMOEGER^S METHOD 



The second method for determining' the organic phosphorus is 

 the one proposed by Schmoeger. Eggert, Nilson, Tache and others 

 have shown that simple ignition increased the solubility of the 

 phosphorus in cold hydrochloric acid. The increased solubility of 

 the phosphorus was believed to be due to the destruction of the 

 organic phosphorus compounds. Therefore, the amount of phos- 

 phorus in the original soil, soluble in cold hydrochloric acid, sub- 

 tracted from the amount in the ignited soil soluble in cold 

 hydrochloric acid of the same strength was regarded as having 

 been derived from the organic phosphorus compounds. This as- 

 sumption was confirmed by Schmoeger by hydrolyzing the soil un- 

 der pressure at a temperature of i4O-i6oC. This treatment of 

 the soil decomposed the organic phosphorus compounds so that the 

 organic phosphorus was rendered soluble in cold hydrochloric acid. 

 The difference, therefore, between the amount of phosphorus ex- 

 tracted from the original soil by cold hydrochloric acid and the 

 amount extracted from the soil which had been hydrolized gave the 

 amount of organic phosphorus. Schmoeger found that, as a rule, 

 concordant results were obtained by the two methods altho in cer- 

 tain cases slightly higher results were obtained by the latter method. 



It was decided to determine the organic phosphorus by both of 

 the above methods. Thus, 10 grams of the original soil was 

 treated with 100 c.c. of 12 percent hydrochloric acid and digested 

 in the cold with an occasional shaking for 24 hours. A second 

 sample of 10 grams was ignited and then extracted with 12 percent 

 cold hydrochloric acid in a similar manner. At the end of 24 hours 

 the extract was diluted with water and separated by filtration. The 

 residue was washed with cold water until the filtrate was free from 

 chlorides: the filtrate was then made up to 500 c.c. and 100 c.c. 

 used for the phosphorus determination. The results recorded in 

 Table 24 show that there are 271 pounds of phosphorus in the 

 original soil soluble in 12 percent cold hydrochloric acid while 

 there are 814 pounds in the ignited soil soluble in the same reagent. 

 These results show, therefore, that there are 543 pounds of organic 

 phosphorus in two million pounds of the surface soil. 



Another sample of 10 grams of the soil was treated with acidu- 

 lated water and heated in an autoclave for 12 hours at a tempera- 

 ture of 1 40- 1 45 C. The sample was then digested for 24 hours 

 with cold hydrochloric acid, filtered and the filtrate made up to 

 500 c.c. An average of two determinations show that 878 pounds 

 of phosphorus were obtained. This would indicate that there were 

 607 pounds of organic phosphorus in two million pounds of the 

 surface soil. Slightly higher results for organic phosphorus are thus 



