An officer or agent of any county, township or municipal corporation who is charged or entrusted with the construction, improvement or keeping in repair of any building or work of any kind, or with the management or providing for any public institution, shall not make any contract binding or purporting to bind the county, township or municipal corporation to pay any sum of money not previously appropriated for the purpose for which such contract is made, and remaining unexpended, and applicable to such purpose, such officer or agent who wilfully or knowingly makes or participates in making a contract without such appropriation or authority, shall be personally liable thereon, and the county, township or municipal corporation in whose name or behalf the same was made shall be not liable thereon.