GASTRIC DIGESTION. 35 



lactic acid interferes with the reaction only in quite concen- 

 trated solution, owing to the hydrochloric acid set free. 



(6) Repeat experiment 5 (a), using a solution (0.25 g. to> 

 1000 cc.) of tropseolin 00, * instead of the methyl violet. 



The reactions may be made sharper by cautious evapo 

 ration of the mixtures (about 30 drops) in porcelain dishes. 



(c) Reactions with Gunzburg's Reagent. 1 g. vanillin, 

 2 g. phloroglucin, 100 cc. alcohol. 2 



1. Add a drop of Giinzburg's reagent to a few drops of 

 the hydrochloric acid solution A, evaporate to dryness in a 

 small porcelain dish over a free flame. Avoid heating too 

 strongly by moving the contents of the dish from side to 

 side and blowing upon it during the heating: purple-red 

 residue. 



Repeat the experiment with the mixtures 2, 3, and 4. 

 The peptone interferes with the Giinzburg reaction less than 

 with the previous ones. Lactic acid does not give the 

 reaction. 3 



II. DETECTION OF LACTIC ACID. 



(a) With Uffehnann's Reagent. To prepare this reagent 

 add to 10 cc. of a 2 per cent, phenol solution a few drops of 

 ferric chloride: amethyst-blue fluid. 



1 Only the tropaeolin with this trade name is to be used. 



3 Giinzburg's reagent cannot be kept long without undergoing change,, 

 and it works best when it is freshly made. The quantities do not make 

 much difference, so that we can prepare the reagent by dissolving as 

 much phloroglucin as may be held on the point of a small knife-blade 

 and the same quantity of vanillin in a few cubic centimeters of alcohol in 

 a test-tube. 



3 An alcoholic solution (0.2 per cent.) of dimethjdamidoazobenzene is- 

 more sensitive towards free hydrochloric acid than Giinzburg's reagent. 

 The yellow solution is changed to red in the presence of free hydrochloric 

 acid. Dilute solutions of the organic acids do not give the reaction.. 

 Filter-paper dipped into the above solution of dimethylamidoazobenzene 

 and allowed to dry may also be used very advantageously to detect small 

 quantities of free hydrochloric acid in the gastric contents. See J. Fried- 

 enwald, Medical Record, April 6, 1895. O. 



