Gallic acid is distinguished from tannic acid by tests (2) and (3). At later stages in the work the potassium, barium, and sodium salts of gallic acid were obtained, and finally the pure acid was made by decomposing the sodium salt with sulphuric acid and crystallizing from water. A portion of the acid so obtained was further purified by dissolving in absolute alcohol and pouring into absolute ether.[20] The melting point behavior of the acid corresponds with that of gallic acid; it melted with decomposition at about 230 deg. For further identification, some of the acid was converted into an ester by the following process: it was dissolved in 80 per cent. alcohol, hydrochloric acid gas was passed in, and the solution was heated an hour on the water bath. It was then evaporated to a small bulk, neutralized with barium carbonate and extracted with ether. The ether, on evaporation, left the ester which was crystallized from water and dried in a desiccator over sulphuric acid. The anhydrous ester agreed in melting point (156 deg. to 159 deg.) and other properties with the ester of gallic acid described by Grimaux.[21] For the sake of comparison, an ester was made from gallic acid obtained from another source and the two agreed in properties. A mixture of the two esters melted within the limits given for the ester of gallic acid. While the tests leading to the identification of gallic acid were being made, another series of experiments was in progress. Eleven and one-half grams of the resin obtained from lead precipitate A by decomposition with hydrogen sulphide were treated with 0.1 n. potassium hydroxide added from a burette until the acid was exactly neutralized. All went into solution. On shaking with ether, some of the potassium salt separated out and was saved for examination. The solution became brown on exposure to air and got darker as the work proceeded. The acid in solution as a potassium salt was precipitated out in four fractions by adding for each fraction one-fourth the amount of 0.1 n. sulphuric acid required to neutralize the potassium hydroxide used. The precipitates were filtered off and examined. The first was small in amount, gummy and hard to filter. The solution was shaken with ether after each precipitate had been filtered off. The succeeding precipitates were in better condition, but were not pure. All appeared to be impure gallic acid which had become brown by absorption of oxygen. They were saved, however, to be tested for poison. After the last fraction had separated, the filtrate was shaken several times with ether and saved for further examination, which will be described under "Rhamnose." This filtrate is designated as B.