82 



Mr. E. C. Grey. Decomposition of 



Volatile Acids. — Under certaia circumstances it has been found that the 

 reduction of mercuric chloride to mercurous chloride in the estimation of 

 formic acid may be accompanied by a blackening indicative of further 

 reduction. It was found that under such circumstances the solution of the 

 sodium salts of the volatile acids obtained from the fermentation gave a 

 precipitate of iodoform when treated in the cold with sodium hydroxide and 

 iodine solution. 



The fact that the production of iodoform in the cold occurred after the 

 solution of the sodium salts of the volatile acids had been concentrated from 

 a volume of 2 litres to 200 c.c, and also tliat the distillate obtained for the 

 estimation of alcohol did not give the reaction, shows that the reducing 

 substance is an acid, and it calls to mind the formation of pyruvic acid 

 observed by Fernbach and Schoen* under the same circumstances from yeast. 

 In this case the amount of acid is very small and no conclusive reaction could 

 be obtained to decide as to its nature. 



The Separation of Sicccinic and Lactic Acids. — The details to which it is 

 necessary to adhere in order that the Pasteur method of separating succinic 

 acid from other acids may yield acciirate results have been described by the 

 writer elsewhere.f 



An important point to note in connection with the present technique is 

 that the absence of peptone obviates the difficulty which was experienced in 

 the earlier experiments in the examination of the residual solution after the 

 distillation of the volatile acids. Also during the distillation itself there is 

 here none of the objectionable frothing to which solutions of peptone may give 

 rise. Chibiiy, however, is it essential that there should be no peptone in the 

 solution which is used for the separation of succinic and lactic acids, as has 

 been pointed out in the special communication referred to. 



TJic Estimatio'ii of Residual Carbohydrate or Allied Substance in the Solution 

 after the Fermentation. — Up to the present the number of substances which 

 could be studied as to the decomposition products resulting from their 

 fermentation has been limited by the difficulty of estimating the portion which 

 remained unferniented after the experiment. It was partly for this reason 

 that the writer introduced the volumetric method of estimating carbon. Even 

 in the case of glucose it may not always be safe to rely upon the figure 

 for the residual portion as indicated by the reduction of copper solution, 

 and certainly the reduction should be determined also after the residual 

 solution (in which the glucose is to be determined) has been hydrolysed 



* Fernbach and Schoen, ' Comptes Rendus,' vol. 157, p. 1478:(1913) ; ibid., vol. 158, 

 p. 1719 (1914). 



t Grey, E. C, ' Bull. Soc. Chim.,' 1917 ; ' Biochem. Journ.,' vol. 11, p. 2 (1917). 



