1. The Reaction

Is determined by means of litmus paper (blue and red). If the filtrate is acid it turns blue litmus paper red.

2. Hydrochloric Acid

Many coloring matters undergo some change when brought together with even weak solutions of free hydrochloric acid. Methyl violet (weak one-per-cent. solution) turns blue; fuchsin is slightly discolored; tropaeolin (saturated solution) turns from yellow to dark red-brown; benzo-purpurin turns from intense red to light red; Congo red (one-per-cent. solution) or Congo paper turns from red to dark blue. Of all these • colors, I think Congo red is the most reliable one. As organic acids when present in considerable quantity may also give these color changes, it is of great importance to have another reaction for hydrochloric acid which the organic acids do not show.

Gunzbarg's Phloroglucin- Vanillin Test

Gunz-burg1 first taught us such a test with his phloroglucin-vanillin solution. This solution contains two parts phloroglucin, one part vanillin, and thirty parts alcohol. The test is made in the following manner: One drop of the filtrate is put on a porcelain dish. A drop of the phloroglucin-vanillin solution is added and well mixed with a glass rod. The porcelain dish is now heated over a spirit lamp and the fluid allowed to evaporate slowly. The presence of even small quantities of hydrochloric acid gives rise to a beautiful cherry-red color. If there be only traces of free hydrochloric acid, the margin of the examined spot turns cherry red.

Boas' 2 Resorcin Sugar Test

The solution consists of resorcin 5.0, sach. albi 3.0, alcohol ad 100. The test is made exactly in the same way as with the phloroglucin-vanillin solution. The hydrochloric acid is recognized by giving a cherry-red color with the Boas reagent. This test is also very reliable, but, as I3 have shown, less sensitive than the Gunzburg reaction.

1 GQnzburg: "Neue Methode zum Nachweis freier Salzsaure im Mageninhalt" Centralblatt f. klin. Medicin, 1887, No. 40.

2J. Boas: "Ein neues Reagens fur den Nachweis freier Salz. saure imMageninhalt." Centralbl. f. klin. Medicin, 1888, No. 45.

3Max Einhorn: "Die neueren Methoden der Magenunter-suchung." New Yorker medicinische Monatechrift, Marz, 188ft.