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 passed by the Council, or be authorized by any officer of the City, except in the cases hereinafter specified, unless the Director of Finance first certifies 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 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.