So much of an act, approved the 12th day of June, 1840, as requires the interest on the public debt of this Commonwealth to be paid in specie or its equivalent, be and the same is hereby repealed; and that the said interest shall be paid by the state treasurer, as the same shall hereafter fall due, in such notes as have been or shall be declared, by any law of the United States, to be lawful money, and a legal tender in payment of debts, public and private, within the United States.