OXIDATION OF SULFUR I\ TIIK SOIL 



249 



It will 1)0 observed, by {ilanciiit? at tiie curves in figure 2, that 

 the hydrogeii-ioii eoncentnition slowly decreases, as manifested 

 by a slow increase in the ]Ai values, with the addition of alkali, 

 till the pH reaches 2.S, then there is a sudden drop in the curve, 

 to i)H ().4, wlien the curve af;ain l)ecomes slanting, followed by 

 a second droj). This o'ves the buffer effect of the cultures; 

 the buffer action is more pronounced in the i)resence of tri-calciuin 

 ])hospha1e, which increases the i)h()sj)hate content of the inediuin. 



3' 



i- 



6- 



7- 



g 





'/f /Vrcenf- of f-r/ei/Zruj/v /lias/'yia^f 

 II or/n/na/ cu/f^or^ 



Amount of a/ua/i ir!~c 



^ 



Fi(i. 2. TiTKATiox CuRVKS OF THE CULTURE OP Thibacillus Ihiooxiilaiis N. SP. 



The sulfur is oxidized into sulfuric acid; this acid acts upon the 

 tri-calciuni iiliosjihate transforming it first into the di-calcium 

 salt, tlien the mono-calcium salt, and finally into phosphoric 

 acid, while the calcium is precipitated as calcium sulfate; further 

 oxidation of sidfur results in the production of free sulfuric 

 acid. 



As to the influence of initial reaction upon growth, we find 

 that a reaction having a hydrogen-ion concentration equivalent 

 to a pH of 2.U-2.S is the most favorable for the growth of the 



