Section 14. The treasurer may, before payment of an account rendered against the county by a county officer, in writing require of him a written statement of the specific provision of law authorizing it, which shall be filed with the vouchers. The treasurer shall be personally liable for money paid out by him, except when specifically required by law, unless there is an unexpended balance of an appropriation made therefor sufficient for such payment, except as provided in section thirty-four, and for any money paid by him without the voucher and certificate required by law.