No contract, agreement or other obligation involving the expenditure of money shall be entered into, nor shall any ordinance, resolution or order for the expenditure of money be issued by the Council, or be authorized by any officer of the city, unless the Mayor and Director of Finance shall first certify in writing to the Council or to the proper officer, as the case may be, that the money required for such contract, agreement, obligation or expenditure is in the treasury, to the credit of the fund from which it is to be drawn, and not appropriated for any other purpose, which certificate shall be filed and immediately recorded. The sum so certified shall not thereafter be considered unappropriated until the city is discharged from the contract, agreement or obligation.