From a tiny glass bottle which he drew from his pocket, the Chief Constable extracted one of the ill-omened darts.
“This is the one which wounded Miss Hawkhurst,” he explained, as he dropped it into a glass of water. “Now we’ll need to give it time.”
He stirred it round occasionally; and gradually a faint bluish tinge communicated itself to the water. Ardsley was scrutinising the glass with deep interest, but his face showed nothing of the thoughts in his mind.
“Now we add a drop of vinegar, Squire,” said Sir Clinton, suiting the action to the word.
As the vinegar mixed with the solution, Wendover saw a change in the tint—a pale red replaced the original blue.
“Now some washing soda, for a change,” said Sir Clinton, dropping in a crystal and swirling the liquid round in the glass. As he did so, the blue tinge returned to the solution.
Ardsley nodded approvingly.
“Litmus, obviously. That clinches it. You must be a bit of a chemist to have hit on that tip.”
Sir Clinton made no reply, but he cautioned Wendover to bear the test in mind.
“If that’s all you want, I’ll go back to Miss Hawkhurst,” Ardsley said, as soon as Sir Clinton ceased speaking.