Such refunding bonds shall bear such rate or rates of interest as may be determined by the board of supervisors, not exceeding, however, three and one-half per centum per annum, payable semiannually; shall be in such denomination or denominations and form as may be determined by the board of supervisors; shall be executed on behalf of the county by the president of the board of supervisors, countersigned by the clerk of such board; and the interest to accrue on such bonds shall be represented by coupons to be attached thereto, which may be executed by the facsimile signatures of such officers. Such refunding bonds shall mature in such amount or amounts and at such time or times, not exceeding twenty-five years from date thereof, as may be specified by the board of supervisors. All such refunding bonds and interest thereon shall be payable at the office of the state treasurer of the State of Mississippi in the city of Jackson, Mississippi, and a certified copy of the proceedings authorizing the issuance of such refunding bonds shall be filed in said office. The bonds issued under the provisions of Sections 65-33-61 through 65-33-71 shall in no way be construed as state obligations or state bonds.