"I want you to come and see my brother," replied our client.
"Why not take a note from me to his doctor?"
"No, no; I want you to come—I should like you both to come—and put a stop at once to this dreadful business. Consider! It's a matter of life and death. You won't refuse! I beg you not to refuse me your help in these terrible circumstances."
"Well," said Thorndyke, as his assistant reappeared, "let us first see what the test has to tell us."
Polton advanced to the table, on which he deposited a small flask, the contents of which were in a state of brisk effervescence, a bottle labelled "calcium hypochlorite," and a white porcelain tile. 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." He dropped a few drops of the hypochlorite solution on to the tile, and immediately the black stain faded away and vanished. "We can now answer your question, Mr. Barton," said he, replacing the stopper as he turned to our client. "The specimen that you brought us certainly contains arsenic, and in very considerable quantities."
"Then," exclaimed Mr. Barton, starting from his chair, "you will come and help me to rescue my brother from this dreadful peril. Don't refuse me, Dr. Thorndyke, for mercy's sake, don't refuse."
Thorndyke reflected for a moment.
"Before we decide," said he, "we must see what engagements we have."
With a quick, significant glance at me, he walked into the office, whither I followed in some bewilderment, for I knew that we had no engagements for the evening.