120 THE DWEST1VE FLUIDS. 



lain or glass, when in the presence of free hydrochloric acid a 

 rose-colored mirror is obtained, which varies in intensity with the 

 amount of the acid. 



Organic acids do not produce the reaction. 



The delicacy of the test is such that the presence of 0.05 gramme 

 of hydrochloric acid in 100 parts of water can he demonstrated. 



BOAS' TEST. The reagent consists of 5 grammes of resublimed 

 resorcin and 3 grammes of cane-sugar, dissolved in 100 grammes 

 of 94 per cent, alcohol. The test is conducted like that of Giinz- 

 btirg, but it is necessary to heat a little more strongly, especially 

 after the fluid has been evaporated. A similarly colored mirror is 

 obtained, which gradually fades on cooling. 



The delicacy of the test is the same as that of Giinzburg. 



Examination for the Presence of Combined Hydrochloric Acid. 

 The presence of combined hydrochloric acid cannot be demonstrated 

 by means of simple tests like those just described, but is inferred 

 indirectly, as shown in the following method : 



Separate Estimation of the Free and Combined Hydrochloric Acid 

 of the Gastric Contents. TOPPER'S METHOD. The total acidity of 

 a given amount of the gastric contents is first determined, as 

 already described, and termed A. This indicates the amount of 

 the physiologically active hydrochloric acid, viz., the free and the 

 combined hydrochloric acid, as well as that of any acid salts and 

 organic acids that may be present. 



In a second specimen the total amount of free acids and acid 

 salts is determined by titrating, as before, with a -^ normal solu- 

 tion of sodium hydrate, but using a few drops of a 1 per cent, 

 aqueous solution of alizarin (alizarin-monosulphonate of sodium) as 

 an indicator. The titration is carried to a point where a pure violet 

 color is obtained. The result is termed B. The difference between 

 A and B is thus referable to the presence of the combined hydro- 

 chloric acid, and termed C. 



In a third specimen the amount of free hydrochloric acid is 

 determined by titrating with the decinormal solution of sodium 

 hydrate, using a few drops of a 0.5 per cent, alcoholic solution of 

 dimethyl-amido-azobenzol as indicator, until the red color which 

 first appears has changed to yellow. The result is termed F. 

 F plus will then represent the amount of physiologically active 

 hydrochloric acid P, viz., the combined and free acid, while the 

 difference between A and P corresponds to the acid salts and 

 organic acids that may also be present. 



M KTHOD OF MORNER AND S.TOQVIST. By this method the amount 

 of physiologically active hydrochloric acid can also be estimated. It 

 is somewhat more complicated and time-consuming than the one just 

 described, but more accurate. It is based upon the fact that on 

 evaporating the gastric contents to dryness in the p'csence of barium 

 carbonate, and subsequently incinerating the residue, the organic 



