GASTRIC ANALYSIS 175 



If it is desired to express the acidity of 100 c.c. of gastric juice in terms of hydro- 

 chloric acid, by weight, multiply the value just obtained by o. 00365. 1 



2. Free Acidity (Organic and Inorganic). Add 3 drops of sodium alizarin 

 sulphonate solution 2 to the contents of vessel B and titrate with N/io sodium hy- 

 droxide solution until a violet color is produced. In this titration the red color, 

 which appears after the tinge of yellow due to the addition of the indicator has 

 disappeared, must be entirely replaced by a distinct violet color. Take the burette 

 reading and calculate the free acidity due to organic and inorganic acids. 



Calculation. Since the indicator used reacts to both organic and inorganic 

 acids, the number of cubic centimeters of N/io sodium hydroxide used indicates 

 the free acidity of 10 c.c. of gastric juice. The data for 100 c.c.. of gastric juice may 

 be calculated according to the directions given under Total Acidity, page 1 74. 



3. Free Hydrochloric Acid. 3 Add 4 drops of di-methyl-amino-azobenzene 

 (Topfer's reagent) solution 4 to the contents of the vessel C and titrate with N/io 

 sodium hydroxide solution until the initial red color is replaced by orange yellow. 6 

 Take the burette reading and calculate the free acidity. 



Calculation. The indicator used reacts only to free hydrochloric acid, hence the 

 number of cubic centimeters of N/io sodium hydroxide used indicates the volume 

 necessary to neutralize the free hydrochloric acid of 10 c.c. of gastric juice. To 

 determine the data for 100 c.c. of gastric juice proceed according to the directions 

 given under Total Acidity, page 174. 



4. Combined Acidity. This value may be obtained by subtracting the number 

 of cubic centimeters of N/io sodium hydroxide used in neutralizing the contents of 

 vessel B from the number of cubic centimeters of N/io sodium hydroxide used in 

 neutralizing A . The data for 100 c.c. of gastric juice may be calculated according 

 to directions given under Total Acidity, page 174. 



5. Acidity Due to Organic Acids and Acid Salts. This value may be conven- 

 iently calculated by subtracting the number of cubic centjpeters of N/io sodium 

 hydroxide used in neutralizing the contents of vessel C from the number of cubic 

 centimeters of N/io sodium hydroxide solution used in neutralizing the contents of 

 vessel B. The remainder indicates the number of cubic centimeters of N/io 

 sodium hydroxide solution necessary to neutralize the acidity due to organic acids 

 and acid salts present in 10 c.c. of gastric juice. The data for 100 c.c. of gastric 

 juice may be calculated according to directions given under Total Acidity, page 174. 



1 One c.c. of N/io hydrochloric acid contains 0.00365 gram of hydrochloric acid. 



2 One gram of sodium alizarin sulphonate dissolved in 100 c.c. of water. 



3 Hydrochloric acid not combined with protein material. 



4 One-half gram dissolved in 100 c.c. of 95 per cent alcohol. 



5 If the orange yellow color appears as soon as the indicator is added it denotes the ab- 

 sence of free acid. 



