The accrued interest and premium, if any, shall be placed in the general obligation bond fund. The purchase price of said bonds shall be placed in the proper improvement fund and applied exclusively to the purposes for which said bonds were voted. When said purposes have been accomplished any moneys remaining in said improvement fund shall be transferred to the general obligation bond fund and when all principal of and interest on said bonds has been paid, the balance of money then remaining in the general obligation bond fund shall be transferred to the general fund.