A massive 19th century mill building on Franklin Street that has languished on the market for years recently sold to a company affiliated with Brady Sullivan Properties of Manchester, one of the state's largest real estate development firms which specializes in converting historic mills into housing. The 310,000-square-foot property at 34 Franklin St., once owned by the former Nashua Corp., sold for $100,000, according to the warranty deed executed Aug. 14 and filed Wednesday with Hillsborough County Register of Deeds.