The commission may appoint a secretary who shall serve during the pleasure of the commission. It shall be the duty of the secretary to keep a full and true record of all the proceedings of the commission, of all books, maps, documents and papers ordered filed by the commission, and of all orders made by each of the commissioners, and of all orders made by the commission or approved and confirmed by it and ordered filed, and he shall be responsible to it for the safe custody and preservation of all such documents at its office. Under the direction of the commission the secretary shall have general charge of its office, superintend its clerical business and perform such other duties as the commission may prescribe. He shall have power and authority to administer oaths in all parts of the state, so far as the exercise of such authority is properly incidental to the performance of his duties or that of the commission. The secretary shall designate from time to time one of the clerks appointed by the commission to perform the duties of secretary during his absence, and during such time the clerk so designated shall, at the office, possess the powers of the secretary of the commission.