An alcoholic solution of the resin was just neutralized with potassium hydroxide. During the titration, the solution rapidly became dark brown. After neutralization it was shaken with ether; the water solution remained brown while the ether layer was nearly colorless and contained practically no dissolved substance. A portion of the water solution of the potassium salt on being acidified with sulphuric acid and standing over night, deposited a slight precipitate. The solution of the potassium salt gave a heavy precipitate with lead acetate somewhat similar to the original lead precipitate A, and also slight precipitates with salts of zinc, mercury, copper, and silver (with reduction). It gave a bluish-black color with impure ferrous sulphate and a dark color with ferric chloride. It reduced ammoniacal silver nitrate and Fehling solution. These experiments indicated the presence of a tannin compound. An alcoholic solution of the resin gave the same color reactions with iron salts as did the potassium salt. To determine which one of the tannin compounds was present was a matter of some difficulty since the di- and tri-hydroxybenzoic acids have in general the same color reactions. The presence of other plant substances in the solution also interferes with the color tests, and finally, a substance which gives a blue color with iron salts and one giving a green color may be found together in the same plant.[19] Further tests with a solution of the resin in dilute alcohol, and with a water solution of the acid precipitated by adding sulphuric acid to a solution of the resin in potassium hydroxide, led to the conclusion that the acid is gallic acid. These tests were the following: (1) Boiling with an excess of potassium hydroxide gave a black substance (tauromelanic acid). (2) The acid was not precipitated by gelatin. (3) On addition of potassium cyanide a transitory red color appeared which reappeared on shaking with air.