There is established a working capital fund of $300,000, to be available without fiscal year limitation, for expenses necessary for the maintenance and operation of (1) a central reproduction service; (2) communication services; (3) a central supply service for stationery, supplies, equipment, blank forms, and miscellaneous materials, for which adequate stocks may be maintained to meet in whole or in part requirements of the bureaus and offices of the Department in the city of Washington and elsewhere; (4) a central library service; (5) health services; and (6) such other similar service functions as the Secretary determines may be performed more advantageously on a reimbursable basis. Said fund shall be reimbursed from available funds of bureaus, offices, and agencies for which services are performed at rates which will return in full all expenses of operation, including reserves for accrued annual leave and depreciation of equipment.