The county commissioners of such county and the corporate authorities of any such city may incur or increase the indebtedness of the county or city to an amount sufficient to pay its share of the real estate required, and of the constructing of the hospital building or buildings aforesaid, together with the necessary equipment therein, by issuing coupon bonds, at a rate not exceeding six per centum per annum and the principal thereof reimbursable at a period not exceeding thirty years from the date of authorization.
16 P.S. § 12116