In all cases where an appropriation of public money is made, and an unexpended balance remains to the credit of the appropriation on the books of the comptroller after the purposes of the appropriation have been accomplished, or after the time has expired within which those purposes may be accomplished, or after a time when the reasons for the appropriation have ceased to exist, the comptroller, upon the receipt of a certificate from the head of the department or other public officer who is charged with the duty of expending the appropriation, stating that all outstanding accounts against the appropriation have been fully paid and satisfied, may, with the written approval of the governor, close out the appropriation account and transfer the unexpended balance to the credit of the unappropriated surplus of the fund from which the appropriation was made.