Whenever any of the money constituting the sinking fund for the redemption of the city debt shall be required for investment as above mentioned, or for the redemption of any city bonds at their maturity, the sinking fund board shall report the amount of money so required to the treasurer, who shall certify the same to the city council, and thereupon the city council shall authorize an order to be drawn on the treasurer, payable from the sinking fund board for such purpose.