At the close of each fiscal year, the unencumbered balance of each appropriation shall revert to the respective fund from which it was appropriated and shall be subject to future appropriation. Any accruing revenue of the city not appropriated as hereinbefore provided, and any balances at any time remaining after the purposes of appropriation shall have been satisfied or abandoned, may be from time to time appropriated by the Council to such uses as will not conflict with any uses from which such revenues specifically accrued. No money shall be drawn from the treasury of the city nor shall any obligation for the expenditure of money be incurred except pursuant to the appropriations made by the Council.