In all cities of the second class A of this Commonwealth, the mayor thereof, in addition to the powers now possessed, is hereby authorized and empowered to designate, in writing, and file with the city clerk of said city, one of the heads of the city departments, entitled to vote as set forth in section four, except the city controller, to act as deputy mayor in case of the necessary absence of the mayor from the city, or his illness or other temporary disability. The person so designated shall be known as deputy mayor, and shall exercise all the powers and discharge all the duties of mayor, during said absence, illness or temporary disability, except the power of appointing to or discharging from office in the city government. Such head of department shall serve without additional compensation; and such deputy mayor shall give bond, to be approved by the city solicitor, in an amount equal to one-half of the bond furnished by the mayor; said bond to be deposited with the city controller. The deputy mayor shall take the same oath of office as that prescribed by law for the mayor. The premium for said bond shall be paid by said city.