If the board has in its treasury any fund set aside for some particular purpose that is not immediately necessary for such purpose, it may by resolution adopted by a majority of its full membership use the money in such fund in the purchase of bonds issued by the board representing an obligation and pledging the credit of the board, and all interest upon such bonds and all moneys paid in redemption of the bonds or realized from the sale thereof shall at once be credited to and placed in such fund.
105 ILCS 5/34-27