For the purpose of carrying out his duties, the Secretary of the Senate is authorized to incur official travel expenses. The Secretary of the Senate is authorized to advance, in his discretion, to any designated employee under his jurisdiction, such sums as may be necessary, not exceeding $1,000, to defray official travel expenses in assisting the Secretary in carrying out his duties. Any such employee shall, as soon as practicable, furnish to the Secretary a detailed voucher for such expenses incurred and make settlement with respect to any amount so advanced. Payments to carry out the provisions of this section shall be made from funds included in the appropriation “Miscellaneous Items” under the span “Contingent Expenses of the Senate” upon vouchers approved by the Secretary of the Senate.