Salt Refining Technology at Zhongjingba Site in Nineteenth-Century Southwest China

Two types of salt stoves (type B with earthen balls, and A without), brine pools, yellow mud processing pits, grooves, and other production facilities are well preserved in the Zhongjingba site in Yushan, Chongqing, China. Those remains can partly reflect how salt was produced in the Yushan area during the Qing Dynasty (1644-1911 CE). To investigate the salt production technology, particularly focusing on the functionality of earthen balls, a comprehensive range of analytical techniques including ion chromatography, X-ray fluorescence, and X-ray diffraction analysis were conducted on earthen balls, soil samples collected from stoves and storages, as well as brine water extracted from nearby wells. The results show that Ca2+ and SO42- were found in higher concentrations than Na+ and Cl- in the brine water; the soil in stoves type A contains sulfur ettringite, while earthen balls in stoves type B contain dihydrate gypsum and calcium phosphate; furthermore, the concentration of Ca2+ and SO42- in stoves type B is higher than that in stoves type A. Thus both stoves types A and B have concentrated brine stove technology. In contrast, stove type B should use "Po-lu-yin-zao" (pour the brine on the stove and allow it to seep into the earthen balls) technology that can make full use of heat, improve the efficiency of salt production and purify sodium chloride from salt springs.