The commissioners of the several counties be and they are hereby authorized, to sell, at public sale, all or any part or parts of the unseated lands which have been purchased for the use of the county, or which hereafter may be purchased from the treasurers of said counties, in pursuance of an act passed on the thirteenth day¹ of March, 1815, entitled “An act to amend an act directing the mode of selling unseated lands for taxes, and for other purposes,” when the lands so purchased have remained unredeemed for five years and upwards, for the best price that can be obtained for the same.