"
He pressed the button of the bell that communicated with the laboratory,
a summons that brought the laboratory assistant from his lair with
characteristic promptitude.
"Will you please prepare a Marsh's apparatus, Polton," said Thorndyke.
"I have a couple ready, sir," replied Polton.
"Then pour the acid into one and bring it to me, with a tile."
As his familiar vanished silently, Thorndyke turned to Mr. Barton.
"Supposing we find arsenic in this arrowroot, as we probably shall, what
do you want us to do?"
"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.
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