318 EXPERIMENT STATION RECORD. 



SOILS— FERTILIZERS. 



Organic phosphoric acid of the soil, C. R. Fraps (Trxufi f^ta. Bui. 136, pp. 

 33). — The author deteriuined the ainoiint of phosphorus soluble in 4 per cent 

 ammonia, and fifth and 1.8-normal nitric acid, in a number of Texas soils before 

 and after ignition. The extraction was made with ammonia directly and after 

 previous extraction with 1 per cent hydrochloric acid, as in the official method. 

 Stewart's ignition method (E. S. R., 23, p. 423) was used, which is in brief as 

 follows : 



"A portion of the soil is ignited, extracted with cold 12 per cent hydrochloric 

 acid, and the phosphoric acid estimated. From this is subtracted the amount 

 of phosphoric acid extracted from the original soil by the same process, and 

 the result is taken to represent the organic phosphorus. Tlae method is based 

 upon the tacit assumption that the effect of the ignition is to destroy the organic 

 phosphorus compounds and so render the phosphorus soluble in acids, without 

 affecting the solubility of the inorganic phosphates." 



The conclusions drawn from this work are as follows : 



" Phosphoric acid is present in the soil as organic phosphates, as phosphates 

 of lime, and as phosphates of iron and alumina. 



" The ammonia-soluble phosphoric acid is partly inorganic and partly organic. 



"Ammonia dissolves phosphoric acid chiefly from phosphates of iron and 

 alumina. 



" Some soils may fix phosphoric acid from ammonia solution. 



" The concentration of the phosphoric acid in ammonia or fifth-normal nitric 

 acid increased with the quantity of soil present, but the parts per million of 

 phosphoric acid extracted from the soil decreased as the quantity of soil was 

 increased. This behavior of the soil phosphates toward ammonia is not in 

 accord with the theory that the ammonia merely combines with organic com- 

 pounds containing phosphorus. 



" The quantities of iron and alumina, lime and magnesia dissolved by the 

 ammonia were small. 



" Phosphoric acid fixed by the soil was partly extracted by acid, partly 

 extracted by ammonia, and a portion remained in the soil. 



" Organic matter added to the soil increases the ammonia-soluble phosphoric 

 acid. As the organic matter decays, the ammonia-soluble phosphoric acid 

 usually decreases, though sometimes it increases. 



"An increase in ammonia-soluble phosphoric acid during decay does not 

 necessarily mean an increase in organic phosphoric acid. 



" Phosphoric acid is dissolved by ammonia from ignited soils. This is evi- 

 dence that the ammonia-soluble phosphoric acid is partly of inorganic origin. 



" More phosphoric acid was dissolved from ignited soils by ammonia, after 

 extraction with acid, than from the same soils before extraction. The increase 

 in ammonia-soluble phosphoric acid brought about by the action of acid on the 

 soil is thus not necessarily entirely due to the liberation of organic compounds 

 containing phosphoric acid, which are dissolved by ammonia. 



"Ammonia has a greater solvent action upon some mineral phosphates (wavel- 

 lite) than has 1 per cent hydrochloric acid. 



" Twelve per cent hydrochloric acid does not extract all the phosphoric acid 

 of wavellite, variscite, or dufrenite. 



"Ammonia extracts more phosphoric acid fi'om wavellite than does 12 per 

 cent hydrochloric acid. 



"An extraction with ammonia following an extraction of the soil with 12 per 

 cent hydrochloric acid may dissolve more inorganic phosphoric acid than a 

 second extraction with 12 per cent acid. 



