The budget may include an item for contingencies. Except in those cases where there is no logical account to which an expenditure can be charged, expenditures shall not be charged directly to contingencies; but instead, the necessary part of the appropriation for contingencies shall be transferred to the logical account, and the expenditure charged to such account. No such transfer shall be made without the express approval of the council, and then only for expenditures which could not readily be foreseen at the time the budget was adopted.