80 



Mr. E. C. Grey. Decomposition of 



By this operation not only is the reaction of fermentation brought to an end 

 and the solution made practically sterile, but a large part of the dissolved 

 carbon dioxide is evolved, so that it is possible to estimate the carbon dioxide 

 which remains in the solution when cold more accurately than when the 

 solution was saturated as in the older experiments. 



Chemical Technique. 



Where no particular method is' indicated it will be understood that tlie 

 methods employed by Harden* and already described have been adhered to. 



The Estimation of Carhon. — It is sometimes of great help in following the 

 course of the fermentation to be able to estimate in a simple manner the 

 carbon dissolved in the solution. This can be done by the volumetric method 

 described by the writer.f 



In cases where the fermentation was interrupted' before the whole of the 

 sugar was fermented an estimation of carbon was made in the solution after 

 the removal of all the products known to be formed, but in no case was any 

 appreciable amount of carbon found in excess of that which corresponds to the 

 sugar present. From this it was concluded that if any glycerine had been 

 left over during the fermentation it was in amount too small to be taken into 

 account. The estimation serves as a check that the whole of the products 

 have been accounted for. 



Carbon Dioxide. — The carbon dioxide which remains dissolved in the 

 fermentation solution is estimated by removing a sample with a pipette and 

 mixing it with a solution of standard barium hytiroxide. This is permissible 

 in the case when the solution is not saturated with gas, as in the experiments 

 described in Part II, but when the concentration of dissolved gas is greater 

 the more accurate method described in Part III is to be recommended. 



The method of collecting the evolved carbon dioxide has been described. 

 The sodium hydroxide used for the absorption is prepared as follows: A 

 known volume of a strong solution of sodium hydroxide is placed in a tall 

 cylinder and a sample of the solution used to determine the amount of carbon 

 dioxide which it contains. Sufficient standard barium hydroxide is added to 

 completely precipitate the whole of the CO2 and the precipitate allowed to 

 settle. The clear fluid is siphoned into a large volume of water which has 

 been previously freed from CO2 by a rapid current of COg-free air. 



The estimation of the amount of carbon dioxide in the original sodium 

 hydroxide solution employed may be made in the apparatus described for the 



* Harden, A., ' Chem. Soc. Journ.,' 1901, p. 610 ; Grey, E. C, ' Eoy. Soc. Proc.,' B 87, 

 p. 472 (1914). 



t Grey, E. C, ' Chem. Soc. Journ.,' 1914. 



