THE METABOLISM OF THE SULPHUR BACTERL4 51 



The carbonic acid is dissociated in two stages : — 



K,{H,CO,) = [U^][HCO,-], . . (I) 



Ki = 3-4 X 10-'^. 

 K.fHCOa) = (hn(C03--), . . (2) 



Ko == 4-6 X 10-11. 



Taking into consideration the ionic product of water, we 

 have 



K^=(H-^)(OH-), . . . (3) 

 K„ = 8 X lo-i^ 



If we indicate the total base as (B^) and note that the sum 

 of the positive ions must equal the sum of the negative ions, 

 we have 



(B-^) + (H+) = (0H-) + (HCO3-) + (CO3-).* . (4) 



If we assume (B^) = o and consider only the carbonate 

 relationship, we have 



(HCO3- 



3-4 X I0-' X (HgCO 



(CO3-) 



(HCO3-) 



(C0.~) 



_ 4-6 X io-ii(HC03) 



= 2-2 X IQI" X H"^. 



Hence in a solution of known pH value we can calculate 

 the relative proportion of bicarbonate ion and carbonate ion. 

 Baas-Becking argues that if putrefactive bacteria were present 

 in sulphur water the HCOs" would increase at the expense of 

 the CO3 , and so alter the value of H"^. But as the pH 

 value is always 7-6 — 8-6 this change does not take place ; 

 hence there are no putrefactive bacteria, and in consequence 

 there is no organic matter, or not enough to make any material 

 difference in the equilibrium of the water. It is surprising 

 that the simple test of ascertaining directly the organic content 

 of the water by estimating the number of saprophytic bacteria 

 in it was not resorted to, in order to prove this conclusion. 

 As to the actual number of bacteria that may be found in such 



* Baas-Becking has inserted 2(C03~) here, which is not correct, but this 

 does not materially affect the equation. 



4* 



