72 Pa. Stat. § 6131
If any tract of unseated land, hereafter to be sold for taxes due at this time, or which shall hereafter be imposed, shall not have bidden for it a sum equal to the whole amount of taxes for which it shall have been advertised, and the costs accrued, then, and in that case, it shall be the duty of the commissioners of the proper county, or any one of them, to bid off the same, and a deed shall thereupon be made by the treasurer to the commissioners for the time being, and to their successors in office, to and for the use of the proper county, and it shall be the duty of the commissioners to provide a book, wherein shall be entered the name of the person as whose estate the same shall have been sold, the quantity of land, and the amount of taxes it was sold for, and every such tract of land shall not thereafter, so long as the same shall remain the property of the county, be charged in the duplicate of the proper collector; but for five years next following such sale, if it shall so long remain unredeemed, the commissioners shall, in separate columns in the same book, charge every such tract of land with reasonable county and road tax, according to the quality of the said land, not exceeding in any case the sum of six dollars for every hundred acres.
72 P.S. § 6131