232 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 10 



As the reaction proceeds to the right in equation (3) the true end 

 point would be indicated by the dissociation constant for HCOi 

 (equation (2) ) and that for equation (4) by the dissociation 

 constant for H,CO,, but H,CO, instead of dissociating at a high 

 acidity as H + and HCOr decomposes to form H,0 and CO, and 

 so does not accumulate in the solution as the free acid. Now if 

 we reverse the scheme and pass CO* into a solution the amount 

 of CO 2 retained by the solution is dependent entirely upon the 

 acidity, both total and actual, of the solution. From the dis- 

 sociation constant for HCO„ 3 X lO -11 , we find that the P H 

 is about 5.3. On the acid side of this point the amount of CO, 

 retained would be very small unless, according to Clark ('20), 

 carbonates were used as buffers. On the alkaline side of 5.3, 

 CO, would be absorbed in proportion to the total alkalinity 

 present and carbonates would be formed (total alkalinity 

 determined by titrating with an indicator that changes at 

 P H 5.3). 



Consider now the situation when the salt of an organic acid 

 such as citric acid is added to the solution and the solution left 

 in an alkaline condit ion, assuming that the salt is sodium citrate. 

 As the citrate radical is oxidized to CO,, H,0, etc., there is a con- 

 sequent accumulation of Na ions in the solution, since the Na 

 cannot be respired into the atmosphere and since it is exceedingly 

 unlikely that it can all be absorbed into the organism and be neu- 

 tralized. Consequently the assumption would be that in order to 

 keep a proper degree of acidity in the protoplasmic mass it is 

 excluded from entering in more than small quantities into the 

 organism. The natural effect of this accumulation of the alkaline 

 ions is the tl end in the alkaline direction. Under these conditions 

 the CO, respired by the bacteria is neutralized with the consequent 

 formation of carbonates, the kind and amount depending directly 

 on the free basic ions, the process beina one of neutralization. 



There 



the idea of 



and others that carbonates per se are split off from the acid 

 molecule; the obvious and direct explanation is that the CO, of 

 respiration is neutralized by the basic ions resulting from the 

 metabolism of the bacteria. Nor would it even be necessary for 

 metallic ions to be present since some of the organic bases might 



