The combined hydrochloric acid may be determined according to Toepfer by titrating with sodium alizarin sulphonate (1 per cent) until the appearance of a violet color, and deducting the found acidity from the total acidity with phenolphthalein as an indicator. Toepfer asserts that alizarin is sensitive for all the elements comprising the acidity except for the combined hydrochloric acid.

In case free hydrochloric acid is absent, and it should be important to ascertain whether combined hydrochloric acid is present, the following method suggested by Sjoequist1 and modified by Ewald2 may be applied: 10 c.c. of the filtrate are mixed with about one-half gram barium carbonate in a platinum capsule. The fluid is then evaporated to dryness and reduced to ashes. After cooling, the residue is dissolved in hot water and filtered. Several drops of a concentrated soda solution are now added to the filtrate. If the fluid remains clear, hydrochloric acid is totally absent. If a precipitate forms after the addition of the soda solution, then the amount of this precipitate will allow us to judge approximately of the quantity of combined hydrochloric acid.

Estimation Of Acid Salts. Leo's Method

The presence as well as the quantity of acid salts is best determined by Leo's8 method. A few drops of the filtrate are put in a watch glass and a small amount of powdered, chemically pure calcium carbonate is added, stirred with a glass rod, and the reaction tested with blue litmus paper. If it turns red, then acid salts are present, for the calcium carbonate combines only with the free acids but not with the acid salts.

1Sjoequist: Zeitschr. f. physiolog. Chemic, 1887, vol. 13, Heft 1-2, p. 1.

2C. A. Ewald: "Diseases of the Stomach," p. 39.

3 Leo: "Eine neue Methode zur Saurebestimnmng im Magenin-halt." Centralbl. f. die mod. Wissenschaft, 1889, No. 26.

Leo's method for determining the quantity of free and combined acid is based on the principle that calcium carbonate neutralizes free and combined hydrochloric acid, but not the acid salts at ordinary temperatures. As the degree of acidity of acid phosphates is larger when calcium chloride is present, and inasmuch as this salt is always developed in small quantities after the addition of calcium carbonate, Leo determines the acidity before and after the addition of the latter, having added calcium chloride to both One proceeds as follows:

After the separation of all organic acids from the filtrate, 10 c.c. (first portion) are taken, and 5 c.c. of a concentrated calcium-chloride solution added and the degree of acidity is determined by phenolphthalein and a decinorraal sodium-hydrate solution.

Fifteen cubic centimetres of the filtrate of the gastric contents (second portion) are again taken and mixed with powdered, chemically pure calcium carbonate and filtered. Of this filtrate 10 c.c. are taken and placed in a bottle provided With a rubber stopper in which are inserted two glass tubes, one short and the other reaching down nearly to the bottom of the bottle. To the upper end of this long glass tube is attached a piece of rubber tubing terminating in a bulb, by means of which air can be introduced into the bottle. After the air has been blown in for some time, in order to drive out the carbonic acid that has formed, the acidity of the solution is determined with phenolphthalein-and decinormal sodium-hydrate solution. By subtracting the figure of acidity obtained from the second portion from that obtained from the first, we have the amount of acidity corresponding to the free and combined hydrochloric acid.

If no organic acids have been present in the filtrate, the last-obtained figure, subtracted from the total acidity, will give the quantity of acid salts.