HYDROCHLORIC ACID. 
Ill 
§83.] 
Acid salts have no action, nor is the test interfered with by large amounts 
of albumins and peptones. 
A. Villiers and M. Fa voile 1 have published a sensitive test for 
hydrochloric acid. The test consists of a saturated aqueous solution of 
colourless aniline, 4 parts ; glacial acetic acid, 1 part. 0*1 mgrm. of 
hydrochloric acid strikes with this reagent a blue colour, 1 mgrm. a 
black colour. The liquid under examination is brought by evaporation, 
or by the addition of water, to 10 c.c. and placed in a flask; to this is 
added 5 c.c. of a mixture of equal parts of sulphuric acid and water, 
then 10 c.c. of a saturated solution of potassic permanganate, and heated 
gently, conveying the gases into 3 to 5 c.c. of the reagent contained in 
a test tube immersed in water. If, however, bromine or iodine (one or 
both) should be present, the process is modified as follows :—The 
hydracids are precipitated by silver nitrate ; the precipitate is washed, 
transferred to a small flask, and treated with 10 c.c. of water and 1 c.c. 
of pure ammonia. With this strength of ammonia the chloride of silver 
is dissolved easily, the iodide not at all, and the bromide but slightly. 
The ammoniacal solution is filtered, boiled, and treated with SH 2 ; the 
excess of SH 2 is expelled by boiling, the liquor filtered, reduced to 10 
c.c. by boiling or evaporation, sulphuric acid and permanganate added 
as before, and the gases passed into the aniline. The process is 
inapplicable to the detection of chlorides or hydrochloric acid if 
cyanides are present, and it is more adapted for traces of hydrochloric 
acid than for the quantities likely to be met with in a toxicological 
inquiry. 
(2) Quantitative Estimation of Free Hydrochloric Acid. —The con¬ 
tents of the stomach are diluted to a known volume, say 250 or 500 
c.c. A fractional portion is taken, say 10 c.c., coloured with litmus or 
phenolphthalein, and a decinormal solution of soda added drop by drop 
until the colour changes ; this gives total acidity. Another 10 c.c. is 
shaken with double its volume of ether three times, the fluid separated 
from ether and titrated in the same way ; this last titration will give the 
acidity due to mineral acids and acid salts ; 2 if the only mineral acid 
present is hydrochloric acid the results will be near the truth if reckoned 
as such, and this method, although not exact for physiological research, 
is usually sufficient for the purpose of ascertaining the amount of 
1 Compt. Rend., cxviii. 
2 To distinguish between acidity due to free acid and acid salts, or to acidity due 
to the combined action of acid salts and free acids, the method of Leo and Uffelmann 
is useful. A fractional portion of the contents of the stomach is triturated with pure 
calcium carbonate ; if all the acidity is due to free acid, the fluid in a short time 
becomes neutral to litmus ; if, on the other hand, the acidity is due entirely to acid 
salts, the fluid remains acid ; or, if duo to both acid and acid salts, there is a propor¬ 
tionate diminution of acidity due to the decomposition of the lime carbonate by the 
free acid. A quantitative method has been devised upon these principles. See Leo, 
Diugnostik der Krankheiten der Verdauungsorgane, Hirschwald, Berlin, 1890. 
