53 Pa. Stat. § 1335
In case the site chosen for such joint municipal building is in land owned and held by the county, it shall be lawful for the county commissioners of such county, and they are hereby authorized and empowered, to incur or increase the indebtedness of the county to an amount sufficient to pay for the cost of the erection of the portion of the building selected by the county and the land upon which it is erected, and any additional land acquired by the county by purchase or condemnation for such site, as well as the unpaid balance of any purchase money on land herein authorized to be conveyed by the county to the city, by issuing coupon bonds in sums of not less than one hundred dollars, each bearing interest at the rate not exceeding five (5) per centum per annum, and the principal thereof reimbursable at a period not exceeding thirty years from the date at which the same are authorized.
53 P.S. § 1335