That for the purpose of ascertaining the compensation to which any person may be entitled under the provisions of section 2* of this act, the board of county commissioners of the proper county shall appoint three disinterested freeholders, electors of the county commissioners, whose duty it shall be to make a true and just estimate, under oath, of the value of all lots to which any owners thereof may be entitled, and shall file the same in the office of the county clerk of the proper county; and the full payment of the sum so estimated and reported by said commissioners, shall be made before the seat of justice of such county shall be moved.