[99] 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 due to both acid and acid salts, there is a proportionate 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, Diagnostik der Krankheiten der Verdauungsorgane, Hirschwald, Berlin, 1890.
The free mineral acid, after extracting the organic acid by ether, can also be saturated with cinchonine; this hydrochlorate of cinchonine is extracted by chloroform, evaporated to dryness, and the residue dissolved in water acidified by nitric acid and precipitated by silver nitrate; the silver chloride produced is collected on a small filter, washed, and the filter, with its contents, dried and ignited in a porcelain crucible; the silver chloride, multiplied by 0·25426, equals HCl.
The best method of estimating free hydrochloric acid in the stomach is that of Sjokvist as modified by v. Jaksch;[100] it has the disadvantage of its accuracy being interfered with by phosphates; it also does not distinguish between actual free HCl and the loosely bound HCl with albuminous matters,—this in a toxicological case is of small importance, because the quantities of HCl found are likely to be large.
[100] Klinische Diagnostik, Dr. Rudolph v. Jaksch, Wien u. Leipzig, 1892. Clinical Diagnosis. English Translation, by Dr. Cagney. Second Edition. London: Charles Griffin & Co., Limited.
The method is based upon the fact that if carbonate of baryta be added to the contents of the stomach, the organic acids will decompose the barium carbonate, forming butyrate, acetate, lactate, &c., of barium; and the mineral acids, such as hydrochloric acid, will combine, forming salts of barium.