GASTRIC DIGESTION. 



125 



cording to the directions given under 2 on page 123. This indicator 

 serves to denote the total acidity since it is acted upon by free min- 

 eral acids, combined acids, organic acids and acid salts. A red 

 color indicates the presence of an alkali and the indicator is colorless 

 in the presence of a neutral or acid reaction. This indicator is 

 unsatisfactory in the presence of ammonia. 

 7. Sodium Alizarin Sulphonate, 1 



CO (OH) 2 



C G H 4 C 6 H 



\ / \ 

 CO S0 8 Na 



This indicator may be used directly in the solution to be tested, or 

 the test may be applied as 2, page 123. It serves to indicate all acid 

 reactions except those due to combined acids. A reddish-violet 

 color indicates an alkaline reaction, while a yellow color indicates 

 an acid reaction due to a free mineral acid, an organic acid or an 

 acid salt. 



Report the results of your tests tabulated in the form given 

 below : 





GENERAL EXPERIMENTS ON GASTRIC 

 DIGESTION. 



i. Conditions Essential for the Action of Pepsin. Prepare 

 four test-tubes as follows: 



(a) Five c.c. of pepsin solution. 



1 Prepare this indicator by dissolving I gram of sodium alizarin sulphonate in 

 100 c.c. of water. 



