Before the board of county commissioners of a county shall issue bonds under the provisions of this chapter the board must first ascertain and determine that the particular bonded, warrant or other indebtedness of the county, proposed to be retired by the bond issue, constitutes binding and subsisting obligations of the county, and they shall thereupon cause a certificate of determination to be made and entered in and upon the records of said board and the findings of said board shall thereafter be conclusive as a basis for the issuance of such bonds and the levy and collection of taxes for their payment.