Section 26. Expenses of offices and departments for compensation of officers, members and employees and for other purposes shall not exceed the appropriations made therefor by the general court or the allotments made therefor by the governor. No obligation incurred by any officer or servant of the commonwealth for any purpose in excess of the appropriation or allotment for such purpose for the office, department or institution which the officer or servant represents, shall impose any liability upon the commonwealth nor shall any liability be imposed upon the commonwealth under a subsequent appropriation by any ongoing commitment against a current year appropriation.