APP. V.] METHOD OF CAHN AND V. MERINO. 499 



3. ADDITIONAL METHODS OF DETERMINING THE ACIDS AND 

 ESPECIALLY THE AMOUNT OF HC1 IN THE GASTRIC JUICE. 



(Supplementary to pp. 95 100 and 178 182.) 



In addition to the methods, which have been described in the 

 body of this work, for the determination of the hydrochloric acid of 

 the gastric juice, a variety of new methods and of modifications of 

 the older methods have within recent times been introduced. It 

 would be impossible even to refer to all of them, and only those 

 which possess special importance and which present peculiar features 

 will be discussed. 



1. The Method of Cahn and v. Mering 1 for the determination of the 

 total hydrochloric acid, the volatile acids and the lactic acid of 

 the stomach contents. 



50 c.c. of the filtered stomach contents are distilled over a naked 

 flame, until three-fourths of the liquid has distilled : the volume of 

 the fluid in the retort is again made up to 50 c.c. and again three- 

 fourths of the fluid distilled off. The distillate contains the volatile 

 acids, the amount of which is determined by tit ration with deci- 

 normal soda. The residue in the retort or flask is shaken six 

 successive times with 500 c.c. of ether, in order to extract the whole 

 of the lactic acid. The united extracts are freed from ether by 

 distillation and the lactic acid determined in the residue by titration. 

 To the concentrated stomach contents, after treatment with ether, an 

 excess of freshly precipitated cinchonin is added, until the reaction 

 becomes neutral, and the mixture is then washed by means of 

 chloroform into a separating funnel and shaken 4 or 5 times with 

 fresh quantities of chloroform. The united chloroform solutions are 

 freed from chloroform by distillation, the residue is dissolved in 

 water, acidulated with nitric acid, and the chlorine present pre- 

 cipitated by adding an excess of silver nitrate. The chloride of 

 silver is determined, lege artis, gravimetrically and the amount of 

 hydrochloric acid corresponding to it calculated by multiplying its 

 weight by 0'25427. 



As will be obvious to the chemist, this method is costly, complex, 

 and difficult, and presents inherent defects which must militate 

 against its accuracy, the chief of which consists in the large quantities 

 of ether which are employed in order to dissolve the lactic acid and 

 which take up not inconsiderable quantities of the hydrochloric acid 

 (Martius and Liittke). 



The process of Cahn and v. Mering, of which the most interesting 

 feature was suggested by a striking experiment of Rabuteau (see 



1 Cahn and v. Mering, ' Die Sauren des gesunden und kranken Magens,' Deutsch. 

 Archiv f. klin. Med. Vol. xxxix. (1886), p. 239. 



322 



