"A large pressure steam box for the Sanford Mills awaits shipment on a Boston & Maine Railroad flatcar outside the company shops. Note the cart on rails to carry materials to be steamed into the pressure chamber. The Portland Company specialized in building very large pressure vessels like this as well as boilers, which are merely high-pressure vessels themselves." --Fletcher, David H. 'The Portland Company 1846-1982.' Charleston, S.C.: Arcadia Pub., 2002. 125.