The flask
was fitted with a safety-funnel and a glass tube drawn out to a fine
jet, to which Polton cautiously applied a lighted match. Instantly there
sprang from the jet a tiny, pale violet flame. Thorndyke now took the
tile, and held it in the flame for a few seconds, when the appearance of
the surface remained unchanged save for a small circle of condensed
moisture. His next proceeding was to thin the arrowroot with distilled
water until it was quite fluid, and then pour a small quantity into the
funnel. It ran slowly down the tube into the flask, with the bubbling
contents of which it became speedily mixed. Almost immediately a change
began to appear in the character of the flame, which from a pale violet
turned gradually to a sickly blue, while above it hung a faint cloud of
white smoke. Once more Thorndyke held the tile above the jet, but this
time, no sooner had the pallid flame touched the cold surface of the
porcelain, than there appeared on the latter a glistening black stain.
"That is pretty conclusive," observed Thorndyke, lifting the stopper out
of the reagent bottle, "but we will apply the final test.
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