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, unless the City Auditor shall first certify 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. The provisions of this section shall not apply to contracts or proceedings relating to improvements any part of the cost of which is to be paid by special assessments.