28 



BULLETIISJ- 782, U. S. DEPARTMENT OF AGRICULTURE. 



spends on the plot to a hydrogen-ion concentration of Pg 7.65. The av- 

 erage hydrogen-ion of the cultures which fermented tliis acid was Pg 

 8.1 ; therefore the alkali produced by the fermentation of this organic- 

 acid salt can not be due to the formation of sodium bicarbonate alone 

 but must be due to sodium carbonate, or a combination of the two. 

 In the 14 acids calculated and shown in Table 12 by similar manip- 

 ulation of the plot, it was found that 6 of the acid salts, namely, 

 citric, malic, succinic, glyceric, tartaric, and malonic produced 

 alkali enough to account for the production of sodium carbonate 

 alone, or the carbonate and bicarbonate together. The remaining 

 acid salts can furnish alkali enough upon complete oxidation to 

 account for the entire alkahnity either through the formation of 

 sodium bicarbonate alone or a combination of the two. These plots 

 do not show exactly the conditions found in the cultures when there 

 is a replacement of a strong acid radical by the weak carbonic acid. 

 Although these plots show only the effect of the addition of car- 

 bonates, they nevertheless clearly indicate the tendency of both the 

 carbonate and bicarbonate to decrease the Pg value of the medium. 

 They further show the relatively weak effect of bicarbonate when 

 the inedium is at a Pg included in the zone where the carbonic- 

 bicarbonate equilibrium is obtained, and indicate very nearly the 

 quantitative effect of the replacement mentioned above provided the 

 acid replaced has a dissociation constant much larger than that of 

 carbonic acid. This last condition does in fact apply to all the acids 

 studied. 



Table 12. — Theoretical carbonate production from organic-acid salts, together loith the 

 average Ph value produced by the alkali-forming bacteria. 



Acid. 



Na2C0 3 ob- 

 tained by 

 complete 

 oxidation of 

 0.01 gram of 

 acid. 



NaHCOs ob- 

 tained by- 

 complete 

 oxidation of 

 0.01 gram of 

 acid. 



Equiva- 

 lent in 

 N/10 alkali. 



Average 

 hydrogen- 

 ion con- 

 centration. 



Citric 



Malic 



Lactic 



Succinic . . 

 Acetic . . 

 Proprionic 



Butyric... 



Mucic 



Glyceric . . 



Tartaric... 

 Malonic . . . 

 Formic . . . 



Benzoic... 

 Salicylic . . 



Gram. 

 0. 008275 

 . 007905 

 .005887 



. 008974 

 .008822 

 .007158 



. 006019 

 . 005165 

 . 004996 



. 007062 



.01020 



.0152 



. 004341 

 . 003838 



Gram. 

 0.01311 

 . 01252 

 . 009333 



.01422 

 . 01399 

 . 01134 



.09541 

 . 007997 

 . 007921 



.01119 

 .01615 

 . 01826 



. 006882 

 . 06084 



C.c. 

 1.562 

 1.490 

 1.110 



1.693 

 1.665 

 1.351 



1.136 

 .9520 

 .9429 



1.333 

 1.923 

 2.169 



.8191 

 .7241 



8.53 

 8.56 

 7.72 



8.32 

 8.00 

 7.42 



7.27 

 7.53 

 8.10 



8.33 

 8.66 

 8.20 



7.15 

 7.25 



When hippuric and uric acids and urea were used no other source 

 of nitrogen was supplied; therefore the organisms had to obtain both 

 their necessary carbon and nitrogen requirements from these com- 



