16 Pa. Stat. § 7377
From and after the passage of this act all contracts made by the commissioners of said county involving an expenditure exceeding one hundred dollars shall be in writing, and shall, immediately after their execution, be filed with the controller; but no contract shall be made, nor the payment thereof certified by the controller, for over three hundred dollars, unless when made with the lowest and best bidder, after due notice to be published by the controller, when directed by the commission, if he approved the purpose of the proposals invited, all bids to be received by the controller, under seal, and to be in his presence opened by the commissioners, and the contracts awarded, of which awards the controller shall keep a record, and he shall certify no warrants for contracts not made agreeably thereto.
16 P.S. § 7377