30 



SULPHUR BACTERIA 



Noting that the solubiUty of HaS = 0-102 when [H+] is 

 about I0~^, then, in equation (i), 



the first term is of the order I0~' X 10"^ X 10"^ = I0~i* 

 ,, second ,, ,, ,, lO"' X lO'^^ X IQ-^ = lO^^s 



,, third „ ,, ,, lO-i* X 10-^ = IO-20 



The second and third terms are therefore neghgible in 

 comparison with the first, 



.-. [H^]3=Ki[H,S][H+] 

 [WY= Ki[H2S] 



= 0-93 X io~^ 

 .-. [H+] = 0-96 X lo-^ 



Baas-Becking obtains the value H"*" = y-d) X lO"^ by using 

 a method of solution which he names the " Cardanus method " 

 (unknown to the author) ; and he has drawn up the following 

 table on the assumption that the metal ions are present in 

 very low concentration (B"*" = lO"^) : — 



The assumption that all the sulphide ions are in attachment 

 to the H-ion seems arbitrary, and from observations of natural 

 waters there appears no warrant for such an assumption. 



In order to present these figures graphically he calculates 

 the logarithm of the concentrations Cg, Ch^s; C^s-, Cg — , 

 and, changing the sign throughout, plots the latter three 

 against the first, which is, of course, the^H of the solution : — 



These results may be presented graphically (Fig. i] 



