Glucose and Mannitol by B. coli communis. 477 



B 



formic acid, another portion being used for lactic acid by Eyffel's method 

 (1909). 



The extent of the correction for carbonic acid and lactic acid in the distil- 

 late of volatile acids may be seen from the figures 

 quoted in the table on p. 478. 



Collection of the Gas. 



The carbon dioxide and hydrogen evolved were 

 in some experiments collected in the apparatus 

 of Harden, Thompson, and Young (1910) ; in 

 other cases a simplified form of this apparatus 

 was employed, which is here figured. The object 

 of this modified form of apparatus is to dispense 

 with all taps and to reduce the number of glass 

 joints. The present form of apparatus has but 

 one glass junction, and has also the advantage 

 that when evacuated it can be sealed by allowing 

 mercury to rise in the inner capillary tube through 

 which the air has been pumped out of the flask. 

 The arrangement for maintaining the pressure in 

 the fermentation flask constant (by adjusting the 

 level of the surface of the mercury in the reservoir 

 automatically) is also of a simpler type. 



The flask A is evacuated by means of the 

 capillary tube, which passes up through the tube B 

 in which mercury rises as the air is removed. 

 The tube from the fermentation flask in the 

 incubator is attached to D by a rubber junction. 

 The gas in the fermentation flask is evolved 

 under atmospheric pressure, this equalisation of 

 the pressure in the flask with that of the atmo- 

 sphere being effected by means of the S-shaped 

 syphon (s), which is filled with mercury and 

 automatically adjusts the level of the surface of 

 the mercury in the mercury reservoir. 



By plunging the rubber tube c beneath mercury 

 and opening the clip K mercury may be allowed v 

 to rise in the capillary tube, and thus the flask A becomes completely sealed 

 from the atmosphere. 



The neck of the flask A may be plunged beneath wax. This substance 



rK 



B 1 



