§ 17. Expenses. The commissioner shall devote his entire time to the duties of his office. The reasonable and necessary expenses of the department and the reasonable and necessary traveling and other expenses of the commissioner, deputy commissioner and other officers and employees of the department, while actually engaged in the performance of their duties, outside of the city of Albany, or if any such officer or employee be in charge of or actually employed at a branch office of the department, the reasonable and necessary traveling and other expenses outside of the place in which such branch office is located, shall be paid from the state treasury upon the audit and warrant of the comptroller, upon vouchers approved by the commissioner.