Section 29. 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 Village Commission, or be authorized by any officer of the village, unless the village clerk shall first certify to the commission 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 village is discharged from the contract, agreement or obligation. The provisions of this section and the requirement of a previous appropriation shall not apply to contracts or proceedings relating to improvements any part of the cost of which is to be paid by special assessment, nor to emergency expenditures in connection with the waterworks, nor to contracts for legal services.