Whenever any city or town of the state of Oklahoma shall have accumulated an amount of money in its sinking fund sufficient to pay at maturity the principal and interest of all its outstanding bonds, coupons and judgments, any surplus money in said fund, after all outstanding bonds, judgments or other charges against said sinking funds have been fully paid, whether maturing in the current or in future years, may be transferred by the governing body of such city or town to its general fund to be used in reducing the ad valorem tax levies for the ensuing fiscal year or years, or in constructing public buildings or other permanent improvements as the governing body may determine.