TRANSFORMATION OF SULFUR 



615 



bination for the production of phosphoric acid.' 59 However, for the 

 maximum transformation of the phosphate, a compost of equal amounts 

 of sulfur and phosphate and a large amount of soil is required. When 

 the compost is inoculated, the reaction takes place much more rapidly. 

 Abundant aeration and optimum moisture offer favorable conditions; 

 small amounts of ferrous and aluminum sulfates exert a stimulating 

 effect. The uncomposted mixture cannot be added as such to the 

 soil since the phosphate will not become soluble under soil conditions. 

 The reaction of the soil would have to be made acid, before the trans- 

 formation would take place. 



Fig. 47. Relation between sulfur oxidation and water-soluble potassium in 

 composts containing sulfur and greensand marl (from Rudolfs). 



The same reactions take place in sterile liquid media inoculated with 

 a pure culture of Th. thiooxidans. By adding 1 gram of powdered 

 sulfur and one gram of chemically pure tri-calcium phosphate to 100 

 cc. of a synthetic solution, sterilizing and inoculating with a pure cul- 

 ture of the organism, the following curves are obtained (fig. 44) . 40 



Composts prepared from greensand and sulfur will allow the libera- 

 tion of small amounts of potassium at pH 2.7 to 2.3 (fig. 47); this 



39 McLean, H. C. The oxidation of sulfur by microorganisms in its relation 

 Co the availability of phosphates. Soil Sci., 5: 251-290. 1918. 



40 Waksman, S. A., and Joffe, J. S. The chemistry of the oxidation of sulfur 

 by microorganisms to sulfuric acid and transformation of insoluble phosphates 

 into soluble forms. Jour. Biol. Chem., 50: 35-45. 1922. 



