None of the funds derived from the sale of said bonds, except so much thereof as shall be necessary to defray the cost of the issuance thereof and the accrued interest from the date thereof to the time of delivery, shall ever be used or expended by said board for any other purposes than those for which authority is herein given to issue the same, as set forth in Section 1 [21-8-15 N.M. Stat. Ann.] hereof.