jpio] CARBON, PHOSPHORUS AND NITROGEN IN SOILS 97 



that the material could be freed from phosphorus only with great 

 difficulty. 



Grandeau (10) regarded the phosphorus associated with the 

 extracted matiere noire as being of the greatest importance, and, 

 was probably in special combination with the organic matter. He 

 regarded it as an index of the fertility of. the soil. 



Simon ( 1 1 ) believed that he had demonstrated that union took 

 place between organic matter and phosphates. When freshly pre- 

 cipitated humic acid was suspended in water and digested with 

 calcium phosphate and then filtered, the filtrate showed an excess 

 of phosphoric acid: this excess, he concluded must be in union 

 with the organic matter in solution. He thought that a double com- 

 pound of ammonia and phosphorus existed in the soil. 



Schultz (12) showed that the addition of humus to "Basalt- 

 boden" increased the absorption ability of the soil for phosphates. 



Eichhorn (13) repeated some of Simon's work and concluded 

 that organic combination did not take place as indicated by Simon 

 but that the humus had decomposed the tri-calcium phosphate with 

 the formation of acid phosphate. 



Pitsch (14) determined the solubility of the various mineral 

 phosphates, including iron and aluminium phosphates, in a solu- 

 tion of ammonium humate itself. He concluded, that, since this 

 solution exerted a solvent action on mineral phosphates, the am- 

 monia extract of the soil contained phosphorus, other than that 

 originally associated with the organic matter in the soil and prob- 

 ably part, at least, of the ammonia soluble phosphorus was derived 

 from the iron and aluminium phosphates. 



M. P. DeGasparin (15) found in calcareous clay soil five per- 

 cent of the total phosphorus in organic combination. He noted, 

 furthermore, that the mosses and lichens contained from 5 to 6 

 times as much phosphorus as the rocks on which they grew ; the 

 soil formed therefore, from the debris of these plants should be 

 relatively richer in phosphorus and should have a part of its phos- 

 phorus in combination with carbon in the organic material. 



Eggertz (21) found that the ammoniacal extract of the soil, 

 when treated with an acid, formed a precipitate of organic matter 

 which always contained phosphorus. He concluded, therefore, that 

 part of the phosphorus of the soil was united to the carbon in or- 

 ganic combination. 



Later, Eggertz and Nilson demonstrated that the amount of 

 phosphorus soluble in dilute mineral acids showed a marked in- 

 crease after ignition of the soil. Ignition rendered 10 times as 

 much phosphorus soluble in 2 percent hydrochloric acid. They 

 attributed this to the destruction of the organic matter which had 

 held the phosphorus in combination which would not yield up its 

 phosphorus to acids. 



