428 PRACTICAL ORGANIC AND BtO-CHEMlSTRY 



(6) 2 c.c. of 0-4 per cent, hydrochloric acid, 2 c.c. of dilute lactic 

 acid and 2 c.c of Witte's peptone solution. 



A survey of the results will be given if the colour be written in the 

 table : 



In performing experiments with gastric contents it may be advis- 

 able to reproduce some of these experiments and compare the colour 

 with these. 



Estimation of the Acids. 



There is no very satisfactory way of estimating the amount of free 

 hydrochloric acid, combined hydrochloric acid and organic acid in 

 gastric contents. Topfer's method of titrating a known volume with 

 (i) phenol phthalein, (2) dimethylaminoazobenzene to an orange yellow, 

 not yellow tint, (3) alizarin red, gives the following information: 



(1) total acids, i.e. free mineral acid + combined mineral acid + 

 organic acid. 



(2) free mineral acid. 



(3) free mineral acid + organic acid, 

 (i) minus (3) combined mineral acid 

 (3) minus (2) organic acid. 



The data are not absolutely correct, but they serve well for com- 

 parative determinations. If the above six mixtures of acids + pep- 

 tone be titrated figures such as the following are obtained : 





