It shall be lawful for, and the right is hereby conferred upon, cities of the second class of this Commonwealth, to sell any of the lands, rights and interests therein, property and franchises, acquired and owned under the rights conferred by this act, or any one or more of them, or any part thereof, if and when the same shall have become unnecessary for their purposes, upon such terms and conditions as may be authorized by ordinance of such cities.
53 P.S. § 25491