QUANTITATIVE ANALYSIS OF MILK. 413 



150 c.c. Cool the solution and dilute it to 200 c.c. in a volumetric 

 flask. Titrate this sugar solution according to directions given 

 under Fehling's Method, page 367. 



Calculation. Make the calculation according to directions given 

 under Fehling's Method, p. 367, bearing in mind that 10 c.c. of 

 Fehling's solution is completely reduced by 0.0676 gram of lactose. 



(b) Quantitative Analysis of Gastric Juice. 

 Topfer's Method. 



This method is much less elaborate than many others but is suffi- 

 ciently accurate for ordinary clinical purposes. The method em- 

 braces the volumetric determination of (i) total acidity, (2) com- 

 bined acidity, and (3) free acidity, and the subsequent calculation 

 of (4) acidity due to organic acids and acid salts, from the data 

 thus obtained. 



Strain the gastric contents and introduce 10 c.c. of the strained 

 material into each of three small beakers or porcelain dishes. 1 

 Label the vessels A, B and C ', respectively, and proceed with the 

 analysis according to the directions given below. 



i. Total Acidity. 2 Add ^3 drops of a I per cent alcoholic solu- 

 tion of phenolphthalein 3 to the contents of vessel A and titrate with 

 Y^y sodium hydroxide solution until a dark pink color is produced 

 which cannot be deepened by further addition of a drop of $$ 

 sodium hydroxide. Take the burette reading and calculate the 

 total acidity. 



Calculation. The total acidity may be expressed in the following 

 ways : 



1. The number of cubic centimeters of y^ sodium hydroxide solu- 

 tion necessary to neutralize 100 c.c. of gastric juice. 



2. The weight (in grams) of sodium hydroxide necessary to 

 neutralize 100 c.c. of gastric juice. 



3. The weight (in grams) of hydrochloric acid which the total 

 acidity of 100 c.c. of gastric juice represents, i. e., percentage of hy- 

 drochloric acid. 



The forms of expression most frequently employed are i and 3, 

 preference being given to the former. 



1 I sufficient gastric juice is not available it may be diluted with water or a 

 smaller amount, e. g., 5 c.c., taken for each determination. 

 a This includes free and combined acid and acid salts. 

 3 One gram of phenolphthalein dissolved in 100 c.c. of 95 per cent alcohol. 



