Each mine inspector may also incur traveling expenses, and such other expenses as may be necessary for the proper discharge of his duties under the provisions of this act. Each mine inspector shall have an office in his district, which may be at his place of residence: Provided, That a suitable room approved by the secretary be set apart for that purpose. The secretary shall have authority to procure for the mine inspectors, on their request, furniture, instruments, chemicals, typewriters, stationery, and all other necessary supplies, which shall be paid for by the State Treasurer, on warrant of the Auditor General, issued upon presentation of vouchers approved by the secretary. All furniture, instruments, plans, books, memoranda, notes and other materials pertaining to the office of mine inspector, shall be the property of the Commonwealth, and shall be delivered by the mine inspector to his successor in office.