A number of chemical tests have been devised for the detection of hydrochloric acid.

Ginzberg's Test For Free Hydrochloric Acid

Phloroglucin............................................ 2

Vanillin................................................ I

Absolute alcohol........................................ 30. Mix.

Two or three drops of this solution are placed on a white porcelain dish and allowed to slowly flow in contact with a similar quantity of filtered gastric juice. The dish is very slowly and gently heated over a spirit flame or Bunsen burner, and if hydrochloric acid is present, a faint rose-red hue appears at the line of contact, which deepens as evaporation continues into a brilliant cherry red. If the acid is abundant, minute cherry-coloured crystals will form. If the acid is feeble, it is best to concentrate the stomach filtrate upon a water or sand bath to about one tenth of its original bulk.

When merely a faint trace of the free acid is present the appearance of the colour should be carefully watched, for it is very evanescent.

Giinzberg showed that one drop of the normal gastric juice - i. e., juice containing 0.2 per cent of free hydrochloric acid - when diluted ten times, should still give the colour. If it appears when the dilution is carried beyond this limit, hyperacidity is present.

This is, on the whole, the most reliable clinical test which has yet been devised, and the ease and quickness of its application for diagnostic purposes has much to recommend it. It requires no special skill, and should always be made, to test the progress of the treatment, while lavage is being performed.

The Boas Test For Hydrochloric Acid

The Boas test is performed in a similar manner to the Günzberg test, but the colour produced varies from rose to vermilion, and the solution is made as follows:

Sublimed resorcin...................................... 5

Sugar................................................. 3

Dilute alcohol......................:................... 100. Mix.

Both tests are only of value from a positive standpoint - i. e., if the colour reaction occurs, free hydrochloric acid is surely present, They are, however, of little or no value as negative tests, for the reason that if peptones or certain other substances are present in the stomach contents the reaction may be entirely obscured. The latter difficulty is met by application of the calcium-carbonate test, which is uninfluenced by other substances likely to be associated with the gastric juice, with the single exception of an excess of acid phosphates.

The Calcium-Carbonate Test

This is conducted as follows: A sample of gastric contents is heated to remove fatty acids, and shaken with ether to remove any lactic acid present, and blue litmus paper is dipped in the fluid. Another blue litmus paper is dipped in a fresh sample of the gastric contents which has been neutralised by the addition of dry pure CaCo3. The redness of the first paper when compared with the second will declare the presence of free hydrochloric acid.

A strong Günzberg reaction usually indicates normal reaction or hyperacidity. Its absence when hydrochloric acid is revealed by the CaCo3 test indicates subacidity. If the latter test fails, then no free acid is present.