The Mayor and Auditor shall supervise all departmental expenditures and shall keep such expenditures within the appropriation. Moneys appropriated as above provided shall not be used for other purposes than those designated in the appropriation ordinance, and all expenditures within the fiscal year shall be made within the appropriations hereinbefore provided for. Council may, however, at any time by resolution with the approval of the Mayor and Auditor, transfer money so appropriated for the use of one department, division or purpose, to any other department, division or purpose; but no such transfer shall be made of money derived from the sale of bonds, or of revenue or earnings of any non-tax supported utility. Any accruing revenue of the City not appropriated as hereinbefore provided may from time to time be appropriated by the Council to such authorized uses as it may by ordinance determine.