"Preston Manutac'turin'ear eighteen hundred and seyenty-eight, may issue from time to time notes, bonds or scrip signed by its treasurer and countersigned by its mayor, to be denomi - nated on their face, Brockton Water Loan, to an amount not exceeding one hundred thousand dollars in addition to the amounts heretofore authorized to be issued by the town or city of Brockton for the same purposes."