The payments herein provided for shall be made by the State Treasurer upon warrants drawn by the Auditor General; and there is hereby appropriated the sum of three thousand one hundred dollars ($3,100), or as much thereof as may be necessary, for payment of the amount accrued to June first, one thousand nine hundred and seventeen; thereafter said payments to be made out of any unused moneys hereafter appropriated for the salary of the head or chief of any department whose office may become vacant.
71 P.S. § 765