It shall be lawful for the Board, in any case where they see fit, to order and allow such expenses of witnesses, and such expenses of or concerning the production of any books, contracts, agreements accounts, or writings, or copies thereof, to or before the said Board, or member thereof, or commissioner or commissioners, as such Board may deem reasonable; and such expenses so ordered and allowed shall be deemed part of the expenses attending the execution of this Act, and be defrayed in the same manner as the general expenses of the Board are now defrayed.