University of Bristol - Historical Photographs of China reference number: WC01-042. See images of salt field windmills on pages 293 and 295 of "Farmers of Forty Centuries" by F.H. King (Jonathan Cape, 1927). The evaporation processes are thoroughly described on pages 291-297.
Sail windmill used in pumping brine, Taku Government salt fields, near Tientsin
Black and white photograph
University of Bristol Library, Special Collections