The Secretary is authorized to establish a working capital fund, to be available without fiscal year limitation, for expenses necessary for the maintenance and operation of such common administrative services as he shall find to be desirable in the interests of economy and efficiency, including such services as a central supply service for stationery and other supplies and equipment for which adequate stocks may be maintained to meet in whole or in part the requirements of the Department and its agencies; central messenger, mail, telephone, and other communications services; office space, central services for document reproduction, and for graphics and visual aids; and a central library service. The capital of the fund shall consist of any appropriations made for the purpose of providing capital (which appropriations are hereby authorized) and the fair and reasonable value of such stocks of supplies, equipment, and other assets and inventories on order as the Secretary may transfer to the fund, less the related liabilities and unpaid obligations. Such funds shall be reimbursed in advance from available funds of agencies and offices in the Department, or from other sources, for supplies and services at rates which will approximate the expense of operation, including the accrual of annual leave and the depreciation of equipment. The fund shall also be credited with receipts from sale or exchange of property and receipts in payment for loss or damage to property owned by the fund. There shall be covered into the United States Treasury as miscellaneous receipts any surplus found in the fund (all assets, liabilities, and prior losses considered) above the amounts transferred or appropriated to establish and maintain said fund. There shall be transferred to the fund the stocks of supplies, equipment, other assets, liabilities, and unpaid obligations relating to the services which he determines will be performed through the fund. Appropriations to the fund, in such amounts as may be necessary to provide additional working capital, are authorized.