Appropriations deposited in and credited to the Senate Contingent Fund or the Assembly Contingent Fund shall be continuously available without regard to fiscal years, except that appropriations made at extraordinary or special sessions for the expenses of said sessions shall be maintained as special accounts within the particular funds and shall be available for expenditure for such purpose for a period of one year after the date upon which the appropriation first becomes available for expenditure, and the unexpended balance of any such appropriation shall revert to the fund from which the appropriation was made upon the expiration of one year following the last day of the period of its availability.