The president judge of the said court of common pleas, or in his absence an associate judge thereof, shall preside during the trial, and shall decide finally all questions of law and evidence that may arise in the case. He shall have the power to issue subpœnas for witnesses, and compel their attendance, by attachment, and the production of books, papers and documentary evidence required or called for by the said court of impeachment, and to punish witnesses and others for contempt, as fully as any court of the commonwealth may lawfully do in any case.