When the particular bonds issued for any bridge or bridges, and the interest thereon, shall have been paid, or a sufficient amount shall have been provided for the payment thereof and held for that purpose as in this article provided, and there remain in said fund a sum or sums of money accumulated from tolls on such bridge or bridges, such money shall be used first for the conversion of such bridge or bridges from a toll bridge or bridges to a free bridge or bridges; and if, after paying the cost of such conversion there remain any sum or sums in such fund, the same shall, upon the determination in writing by the commissioner to the State Auditor that such conversion has been completed, and that there are no outstanding claims against such bridge or bridges by reason of the same and having been operated as toll bridge or bridges, such remaining sum or sums of money shall be transferred to the state secondary road fund.
