Every municipal corporation and the officer or officers of any municipal corporation in this state who are charged with the custody of funds raised in pursuance of Article IX, Section V, Paragraph VI of the Constitution of this state are required, under the direction of the mayor and council of the municipal corporation or a duly constituted and authorized committee of the same, to invest, within six months from their collection, all sums collected by the municipal corporation under the requirements of such paragraph of the Constitution, for the purpose of paying the principal of the bonded indebtedness of the municipal corporation, which sums are not actually payable on such principal within 12 months from the date of collection thereof. Such sums may be invested in valid outstanding bonds of such municipal corporation or of some other municipal corporation in this state of equal or larger size, which bonds have been duly validated in accordance with law, or in county bonds of this state which have been duly validated, or in valid outstanding bonds of this state or of the United States. The officer or officers of the municipal corporation shall keep such funds so invested in such bonds, with the privilege of changing the investment from one character of the bonds named to another from time to time as the mayor and council may direct, until such time before the maturity of outstanding obligations as may be necessary to dispose of the same in order to meet such obligations at maturity.