About 5 grams of the poisonous tar free from gallic acid and sugar was
dissolved in alcohol, and dilute (2 per cent.) sulphuric acid was added.
Some of the tar separated out on diluting the alcohol with the acid. The
mixture was heated on a water bath during work hours for four days. A
purple and green fluorescent solution was formed, though much tar was
left apparently unchanged. The alcohol was evaporated off and the
solution was filtered from tar. The fluorescent filtrate was shaken
with ether, by which the green substance was removed, leaving the
solution purple. The ether left, on evaporation, a small quantity of a
green substance having a pleasant ester odor. It was not further
examined. A portion of the purple solution was exactly neutralized with
sodium carbonate. This solution gave a blue-black color with ferric
chloride which became red on addition of another drop of sodium
carbonate, indicating gallic acid. It also reduced Fehling solution.
Another portion of the purple solution was made alkaline with sodium
carbonate. A reddish-brown flocculent precipitate was formed and was
filtered off. The filtrate did not give any color with ferric chloride,
but it reduced Fehling solution. It also gave the test for rhamnose with
alpha-naphthol.
The main portion of the purple solution was made alkaline with sodium
carbonate; the precipitate was filtered off and dissolved in acetic
acid. This solution was yellow and gave a reaction with ferric chloride
similar to that of gallic acid. The filtrate from the precipitate by
sodium carbonate was concentrated by evaporation until sodium sulphate
began to crystallize out. Alcohol was added to precipitate the sodium
sulphate completely, the mixture was heated and filtered. The alcoholic
filtrate was concentrated to a syrup which reduced Fehling solution and
gave the characteristic tests for rhamnose already described. By this
hydrolysis, the tar was split up into rhamnose and some form of gallic
acid which could be precipitated by sodium carbonate. This compound,
whose acetic acid solution was yellow, probably contained fisetin also.
The reason for this last statement will appear from the following
experiment: