498 QUANTITATIVE DETERMINATION OF ACIDITY. [BOOK II. 



In the opinion of the Author, however, the method of the ' coefficient 

 de partage/ &c. offers the most direct, as well as the simplest manner 

 of settling the question. 



2. Quantitative determination of total acidity. 



In determining the acidity of the contents of the stomach it is 

 absolutely essential, as Martius and Ltittke have conclusively proved, 

 (1) to employ the unfiltered contents instead of, as has hitherto been 

 the practice, the filtrate separated from the solid matters held in 

 suspension, inasmuch as the degree of activity of the latter stands 

 in no definite relation to the fluid which surrounds them. 



20c.c of the thoroughly shaken contents of the stomach are measured 

 by means of a graduated flask, and, after the addition of 3 to 4 

 drops of solution of phenolphthalein, are diluted, in another graduated 

 flask, to the volume of 300 c.c. After thoroughly shaking, 150 c.c. 

 of this mixture are poured into each of two beakers possessing a 

 capacity of 200 c.c. and which are placed, side by side, on a sheet of 

 white paper. Decinormal solution of sodium hydrate is then allowed 

 to flow from a burette into one of these beakers, until the red 

 reaction just appears. The transition in tint can be readily observed,, 

 if both beakers are looked at, side by side. Having made the first 

 determination, it is repeated with the second portion. 



In accordance with the very practical suggestion of Ewald, it is 

 now the practice to express the value of the total acidity of gastric 

 juice not in terms of the absolute amount of alkali required to 

 neutralise 100 c.c. of gastric juice, but by the number of cubic 

 centimetres of decinormal solution of sodium hydrate employed for 

 the same purpose. Thus if we state that the acidity of the gastric 

 contents equals 50, we signify that 100 c.c. would be neutralised by 

 50 c.c. of decinormal sodium hydrate. 



3. Quantitative determination of Free Acids. 



This determination is carried out as the determination of total 

 acidity ; solution of tropseolin (1 part to 10 of diluted spirit) is, 

 however, substituted for phenophthalein. The transition from yellow 

 to red is readily seen when the contents are suitably diluted and the 

 quantity of the diluted fluid is not too great. About 50 c.c. should b& 

 employed 1 . 



1 Martius and Ltittke, op. cit. pp. 66 and 67. 



