The state treasurer may borrow from any fund in his custody, deposited with him pursuant to law, a sum sufficient to pay the principal and interest on any state debt or other obligation due and owing, and repay the same out of the first taxes or other revenue received into the treasury and dedicated to the payment of such principal and interest. He shall not, however, borrow, appropriate or use any part of the fund for the support of free schools or money appropriated for that purpose or received into the treasury under the provisions of any law passed to augment such fund.