THE ACID OF THE C\ ISTRR 'JUICE. 365 
less influenced 1>\ 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 it' the test gives a 
positive result this may usually be relied upon. 
The best of these reagents arc the following : — (a) Gunzberg'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 not succeed in the presence of 
proteids or leucine : it is said to detect 1 part of free acid in 20,000. (b) The 
tropceolvn test. — Drops of a saturated solution of tropseolin 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) Reach's test' 1 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 :J has modified this test into 
a quick, colorimetric quantitative method. He finds the Keoch 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, niethylaniline-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. — 
Mbrner and Sjoqvisf's method. 6 — 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 grms. 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. 
- Journ. Anat. and Physiol., London, 1874, vol. viii. p. 274. 
8 Ztschr. 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 Ztschr. f. physiol. Chem., Strassburg, 1889, Bd. xiii. S. 1. See also Sjoqvist, Shorn-] in. 
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. 
