That all cities in the State of Oklahoma operating under a charter form of government, wherein such cities may hereafter issue bonds for the purpose of raising funds to construct a city hall building, be and are hereby required to pay into the sinking fund for the payment of interest and the retirement of such bonds so issued, all rentals so derived from the use of such parts of the city hall building as are not required for the use of the city, and such rentals so acquired over and above maintenance shall be irrevocably pledged for the payment of the interest and the retirement of such bonds and shall not be used for any other purpose.
Laws 1925, c. 39, p. 60, § 1.