(a) Shall not exceed ten per centum of the total of the amounts otherwise appropriated for the purpose for which such fund is established; and
(b) Shall be raised by a tax levied only upon such real estate as shall be liable to taxation for the purpose for which such fund is established. 4. The board of supervisors by resolution pursuant to section three hundred sixty-three may at any time appropriate all or any part of the moneys in a contingent fund established pursuant to subdivision three of this section for the purpose for which the contingent fund was established. Moneys in the contingent fund shall be used for no other purpose.