94 



Mr. E. C. Grey. Decomposition of 



In order to ascertain the amount of carbon dioxide whicli has been 

 produced up to any moment of the fermentation, it is necessary to estimate 

 the gas which has been absorbed by the alkali in the bottles, L', L", L'", 

 the amount which is present in the fermentation solution, and the amount 

 which is in the gas space in the fermentation flask. These two last must 

 be determined simultaneously owing to the possibility of repartition of the 

 carbon dioxide between the two media by diffusion. The arrangement of 

 the apparatus permits of this simultaneous determination. The taps F 



and K are closed, and H and G opened ; mercury is thus drawn up into the 

 burette ; G is then closed. A sample of the solution in the flask is removed 

 for the estimation of dissolved carbon dioxide by connecting an evacuated 

 flask containing a quantity of standard barium hydroxide solution with the 

 tube B and opening the pinchcock C, as described in the section on the 

 estimation of carbon dioxide. At the instant that the sample of solution is 

 removed, the tap F is opened, and a sample of gas thus drawn into the gas 

 burette by the fall of the mercury. A small piece of solid potassium 

 hydroxide is allowed to float up into the burette for the absorption of the 

 carbon dioxide in the sample of gas. 



