If, in order to maintain sufficient monies on demand deposit in any fund as provided in § 1-705, it becomes necessary to transfer or sell any securities of such funds, the officers specified in § 1-706 may transfer said securities to any other fund or funds in which there are temporarily idle monies, or shall sell such securities, and for such purpose they shall have authority to make any necessary written direction, endorsement or assignment for and on behalf of the city.