OXIDATION OF STJLFUK IN THE SOIL 



241 



2.6-2.8, the reaction remained stationary till all the tri-calcium 

 phosphate had been transformed into mono-calcium salt, after 

 which the reaction became more acid, as shown in table 1 and 

 figure 1. 



All attempts to grow the sulfur-oxidizing organisms on solid 

 media failed, neither agar nor silica-jelly media allowing any 

 growth to take place. 



TABLE 1 

 Course of reaction and accumulation of water soluble phosphates 



•Medium contains originally 1 per cent insoluble phosphate. 



A pure culture was obtained by continued transfer in fresh 

 flasks with high dilutions, so as to eliminate any contaminating 

 organism, the medium being made acid at the start (pH 2.0- 

 3.0), by the use of phosphoric acid and mono-potassium phos- 

 phate. The culture was finally obtained in a pure state. Its 

 purity was demonstrated by repeated microscopic examinations, 

 by the uniform growth in the liquid media and by the fact that 

 no organism developed, when the culture was inoculated upon 

 common bacteriological media. 



