THE ACID OF THE GASTRIC JUICE. 365 



less influenced by the presence of proteid or peptone, and cannot be 

 much depended on for proving the entire absence of hydrochloric acid. 

 The quantity of organic acid required to give the reaction in each case is 

 much in excess of that present in the stomach, so that if the test gives a 

 positive result this may usually be relied upon. 



The best of these reagents are the following : (a) Gunnery's reagent, 1 

 which consists of 2 parts of phloroglucinol, 1 part of vanillin, and 30 parts of 

 absolute alcohol. A few drops of this reagent and a few drops of filtered 

 gastric juice are evaporated to dryness together, when, if free hydrochloric 

 acid be present, a carmine-red mirror or carmine-red crystals are obtained. 

 The test is unaffected by organic acids, but does hot succeed in the presence of 

 proteids or leucine ; it is said to detect 1 part of free acid in 20,000. (b) The 

 tropceolin test. Drops of a saturated solution of tropaeolin in methylated spirit 

 are allowed to evaporate on porcelain ; to the stain so left a drop of the solu- 

 tion to be tested is applied, and the drop is evaporated at 40 C. In the 

 presence of hydrochloric acid the result is a violet stain. The test has about 

 the same delicacy as Gunzberg's, and is subject to the same objections. 

 (c) Reoch's test 2 consists of a mixture of citrate of iron and quinine, and of 

 potassium sulphocyanide. This is coloured red by a trace of a mineral acid, 

 but not by dilute solutions of organic acid. Szabo 3 has modified this test into 

 a quick, colorimetric quantitative method. He finds the Reoch test a satis- 

 factory one, unaffected by chlorides, peptones, or the usual amount of lactic 

 acid present in gastric juice. (d} Congo-red is strongly recommended by 

 Gamgee, 4 either in aqueous solution, or as test paper made by saturating filter 

 paper with it, and then drying. Traces of hydrochloric acid turn it an intense 

 blue, while organic acids give a violet tint. 



Gentian-blue, methylaniline-violet, malachite-green, and benzo-purpurin 

 are other reagents which have been recommended as colour tests for traces of 

 free mineral acids. 



Quantitative estimation of the free hydrochloric acid of the gastric juice. 

 Mb'rn&r and Sjoqvist's method^ This method consists essentially in con- 

 verting all the acids present into barium salts by shaking up with barium 

 carbonate, drying, incinerating, and extracting thoroughly with warm water. 

 In the process of incinerating, the barium salts of the organic acids which may 

 have been present are destroyed and barium carbonate is reformed ; the barium 

 chloride formed from the hydrochloric acid alone dissolves afterwards, and 

 gives, by estimating the barium, a measure of the amount of hydrochloric acid 

 present. Using litmus as an indicator, 10 c.c. of the gastric juice is neutralised 

 with finely-powdered barium carbonate in a platinum evaporating dish. The 

 mixture is dried on the water bath, the residue incinerated, the ash powdered, 

 extracted with as little warm water as possible, and finally filtered. The 

 filtrate should measure about 50 c.c. To this filtrate an equal volume of 

 absolute alcohol is added, and then three or four drops of a solution containing 

 10 per cent, each of sodium acetate and acetic acid. Into this solution a 

 standard solution of potassium bichromate, containing 8 '5 grins, per litre, is 

 run from a burette until all the barium is precipitated. The alcohol added 

 aids the precipitation, and the acetate solution prevents the precipitation of 

 calcium salts or the formation of any free hydrochloric acid. " Tetra 



1 Chem. Centr.-Bl., Leipzig, 1887, S. 1560. 



2 Jonrn. Anat. and Physiol., London, 1874, vol. viii. p. -274. 



3 Ztsclir. f. physiol. Chem., Strassburg, 1877, Bd. i. S. 152. 



4 "Physiological Chemistry," London, 1893, vol. ii. p. 94, where a full account of 

 these colour tests may be found. 



5 Ztsclir. f. physiol. Chem., Strassburg, 1889, Bd. xiii. S. 1. See also Sjoq vis t, SJcandin. 

 Arch. f. Physiol., Leipzig, 1895, Bd. v. S. 277, where a full history of this subject is given, 

 and a bibliography of over 150 memoirs on the subject. 



