vi4^10 MANUAL OF METHODS FOR PURE CULTURE STUDY 



X0.022 = grams of CO2 (i.e., 1 ml. of N/10 Ba(0H)2 converted into the carbonate 

 represents 0.0022 g. CO2.) 



The contents of the culture arm of the Eldredge tube may be ana- 

 lyzed, if desired, to show the amount of sugar remaining, by the 

 methods given above (p. VI42-7). One can strike a balance between the 

 CO2 given off and the sugar-carbon consumed, and thus decide wheth- 

 er to look for other end-products. This makes the Eldredge tube 

 method a useful preliminary in some cases for a more extensive study 

 of the fermentation. 



Hydrogen. Hydrogen is usually determined in one of two ways: 

 by measurement of volume; by combustion to water and determina- 

 tion of the water by weight. In the first procedure the gas produced 



Fig. 1. The Eldredge Tube 

 Height 4", width 3>^", length horizontal tubes, 4^". 



in the fermentation may be collected over alkali, and in the absence 

 of other gases such as methane, the hydrogen measured directly. 

 Also the gas may be exploded in a Hempel pipette, and the decrease 

 in volume of gas measured. When methane is present, the CO2 

 formed by its combustion must be mea^ared and a correction ap- 

 plied (cf. Gas Chemists' Handbook, 1929; McCulloch, 1938). 



The combustion of hydrogen to water may be brought about by 

 CuO at 250° C. Methane is not oxidized under these conditions. The 

 water is collected in a suitable train and weighed. 



Acetyl-methyl-carhinol. A minor by-product, which has come into 

 prominence because of its detection in the Voges-Proskauer test for 



