PHOSPHORUS 175 



the phosphates of bone and to a less extent that of mineral phos- 

 phates. The greatest solvent action was exerted in media contain- 

 ing sodium chlorid, potassium sulphate, and ferrous sulphate. Even 

 yeast may be important in dissolving phosphates. As suggested 

 by Krober the life activity of the bacteria, that is, assimilation of 

 phosphorus by the living organism, probably plays little or no direct 

 part in dissolving the phosphates, but it is due to the action of the 

 organic acids and of the carbon dioxid produced. 



The acids produced by bacteria act upon all phosphates, convert- 

 ing them into the soluble monophosphate, but the rate of solution 

 varies widely with the different phosphates. Tricalcium phosphate 

 in precipitated form, dicalcium phosphate, and tetracalcium phos- 

 phate of Thomas slag are much more rapidly dissolved than the 

 crystalline or the so-called amorphous phosphates. The general 

 reaction is as follows : 



2RCOOH + Ca 3 (PO 4 )2->Ca 2 H2(PO4)2 + (R COO) 2 Ca 



The reaction takes place most rapidly in soils containing large 

 quantities of organic matter due to the active fermentation taking 

 place in such soils. 



Grazia considers enzyme action to play a part in the dissolving 

 of phosphates in soil, for he found the addition of chloroform to a 

 soil reduced bacterial activity and decreased the acid produced, but 

 at the same time the solution of phosphates was increased. This is 

 in keeping with the finding of Bychiklin. 



The presence of ammonium chloride and sulphate in the cultural 

 media is especially effective in increasing the solvent action of 

 bacteria, according to Perotti, who considers the successive steps 

 in the solution or decomposition of phosphorus compounds by 

 bacteria as follows: (1) generation of acids, (2) secondary reactions 

 in the solution, and (3) production of a soluble phosphorus contain- 

 ing organic substance. The first two of these are the result of 

 the activity of the bacteria on the phosphorus, and the last is due 

 to the metabolic assimilation of the microorganisms. 



The oxidation of sulphur by soil bacteria may at times generate 

 sufficient acid to play a very important role in dissolving soil phos- 

 phorus. Hopkins and Whiting, however, consider that the nitrite 

 bacteria are of the first importance in rendering phosphorus and 

 calcium soluble when they oxidize ammonia into nitrites: 



(NH 4 )2C0 3 + 3O 2 2HN0 2 + H 2 CO 3 + 2H 2 O 



The resulting nitrous acid then reacts with the raw rock phosphate, 

 rendering it soluble, thus : 



Ca 3 (P0 4 ) 2 + 4HNO 3 = CaH^PO^ + 2Ca(NO,) 2 



