156 



LAURENCE F. FOSTER AND SAMUEL B. RANDALL 



increases. That such a condition is abnormal is, of course, quite 

 obvious, but the experiment serves to indicate that CO2 may not 

 be ruled out as a factor in causing acidity increases in media upon 

 standing. 



TABLE 6 

 Experiment II 



Ph after autoclaving . 



Ph after exposure to CO2 for 24 hours 

 Ph (control) after 24 hours 



5.35.65.86.06.26.5 



5. 35. 45. 55. 6|5. 75. 8 

 5.35.65.86.06.26.5 



7.1 

 5.9 

 7.1 



7.4 

 6.1 



7.4 



7.6 

 6.2 

 7.6 



7.9 

 6 2 

 7.9 



8.3 

 6.3 

 8.3 



8 4 

 6.4 



8.4 



Experiment III. 



The effect of exposure of sterilized hroth to an 

 atmosphere free from CO2 



Tubes of the medium prepared in the preceding experiment were 

 autoclaved and treated as follows: (1) Control, allowed to stand 

 at room temperature. (2) Placed in a C02-free atmosphere. 

 Ph readings were made at the outset, after seven days, and after 

 fourteen days. To obtain atmosphere free from CO2 air was 

 drawn through a train of Woulff bottles containing concentrated 

 NaOH, 20 per cent Ba(0H)2, and CaCl2 into a large Navy jar 

 containing the tubes of media. 



By inspecting table 7, it will be noted at once that practically 

 the same changes in Ph occurred in both sets of tubes. This 

 would seem to dispose of atmospheric CO2 as a factor operative in 

 causing the increases in acidity so frequently noted in the previ- 

 ous experiments. 



TABLE 7 

 Experiment III 



Ph after autoclaving 



Ph after 7 days in atmosphere. . 

 Ph after 7 days in C02-free air . 

 Ph after 14 days in atmosphere. 

 Ph after 14 days in COz-free air . 



5.1 

 5.2 

 5.1 

 5.0 

 5.0 



5.3 

 5.5 



5.4 

 5.4 



5.4 



5.8 

 5.8 

 5.8 

 5.8 

 5.7 



6.16.36.6 

 6. 16. 416. 6 

 6.06.4|6.6 

 6.16.46.6 

 6.06.36.6 



7.0 

 7.1 

 7.1 

 7.0 

 6.9 



7.2 

 7.4 

 7.4 

 7.3 

 7.3 



7.6 



7 

 7 

 7 



8.0 

 8.0 

 8.0 

 8.0 

 7.9 



8.5 

 8.3 

 8.3 

 8.4 

 8.3 



8.7 

 8.6 

 8.6 

 8.6 

 8.4 



Assuming that the external factors of glassware and atmospheric 

 CO2 are not sources of change in reaction of broth media it will 

 be necessary next to examine the internal factors, namelj^, the 

 possibihty of chemical changes in the medium itseK. The organic 



