Glucose and Mannitol hy B. coli communis. 



93 



to analysis. By a comparison of these analyses the amounts of the various 

 products which had been formed during each interval of time would be 

 determined. 



Certain modifications were necessary in the form of apparatus used and 

 in regard to the analysis. With regard to the analysis, the estimation of 

 carbon dioxide from time to time during the course of the experiment 

 required a special device. In the first place, the gas space above the 

 solution would gradually increase as the samples of solution were removed, 

 and diffusion from the solution to the space above would cause the con- 

 centration of CO2 in the solution to be constantly changing, and in the 

 second place, since the sample of the fermentation solution would have 

 to be removed while warm, precautions would have to be taken to avoid 

 loss of CO2 prior to its mixture with standard barium hydroxide solution. 

 The apparatus was therefore arranged according to the plan represented in 

 the figure below. 



Arrangement of Apparatus for the Study of the Various Phases of a 



Fermentation. 



The essential differences between the apparatus for the study of the 

 fermentation in stages, and that (fig. 1 of Part II) for the case of a complete 

 fermentation are — the flask A for the withdrawal of the samples of the 

 solution ; the gas burette H for the removal of samples of gas and estimation 

 of the carbon dioxide ; and the arrangement of the three-way tap K by 

 means of which the system of bottles, L', L", L'", containing the alkali for 

 the absorption of the carbon dioxide evolved during the fermentation, may be 

 shut off from connection with the fermentation flask D, while the hydrogen 

 which has collected in the reservoir M is returned to the fermentation flask 

 to replace the volume of the liquid removed at A. 



The method of operating is as follows : — The flask D at the beginning of 

 the experiment contains about 5 litres of solution, and the air space above 

 the liquid is about half a litre. The pinchcock C is closed, the taps H 

 and K are closed, and F and G are opened. By the aspiration of the water- 

 pump with which G is in connection, the flask D is deprived of air, the 

 solution being brought to the boil under the reduced pressure. Nitrogen 

 is introduced through the tube B after removal of the flask A. During the 

 course of the fermentation the three-way tap K is turned so that the evolved 

 gases pass through the bottles, L\ \?, ]J, into which a known amount of 

 C02-free alkali has been introduced. The bottles are arranged so that they 

 may be readily removed, and the amount of carbon dioxide absorbed 

 determined. 



I 2 



