84 THE GASTRIC JUICE. 



The common tests for the detection of hydrochloric 

 acid cannot he employed in the case of the gastric juice, 

 because the soluble chlorids which are usually present will 

 respond to them. Special tests are used, most of which are 

 based upon the fact that certain organic coloring matters 

 are changed in color by a comparatively strong mineral 

 acid, like hydrochloric, even in the dilute state, but are not 

 affected by the weaker organic acids or acid salts. While 

 these methods are not absolutely accurate, they are suffi- 

 ciently reliable for clinical purposes when carefully per- 

 formed. 



Many methods have been proposed for determining 

 the amount of hydrochloric acid. * Sjoqvist's method gives 

 accurate results. The juice is evaporated with barium car- 

 bonate, which contains no chlorids. The acids unite with 

 the carbonate, forming barium salts. The dry residue is 

 ignited in a crucible, when the salts of the organic acids 

 are destroyed, the barium chlorid remaining unchanged. 

 This is dissolved with hot water and the amount deter- 

 mined by a standard solution of potassium dichromate. 

 This is added until the barium is precipitated and there is 

 a slight excess of the dichromate. The amount of dichro- 

 mate used corresponds to the amount of barium present, 

 and from this the hydrochloric acid is calculated. Toepfer's 

 method is not difficult and the results are good. 



198. TESTS FOR FREE HYDROCHLORIC ACID. Make 

 some 0.2-per-cent. hydrochloric solution as in Experiment 

 179, and apply the following tests: 



a. Add a methyl-violet solution. The color changes 

 from violet to blue. 



6. Add a solution of tropaaolin 00. The yellow color 

 is changed to a red. 



