Archaeologists have discovered a 2,400-year-old filter that was used to extract salt from seawater in North China.

Ancient Chinese in coastal areas used to extract salt from seawater, by using a filter that would be placed under a caldron containing seawater blended with plant ash, said Wang Lingfeng, director of the office for protection of cultural relics in Haixing County, Cangzhou City of Hebei Province.

The filter is believed to be from the Spring and Autumn Period (770 BC-476 BC) and was in good condition when it was found in Haixing County, Wang said.

The helmet-shaped filter is 22 cm tall with the inside diameter of 13.7 cm and the outside diameter of 19.5 cm. Winding gullies were found inside the filter.

Along with the filter, a drain, fragments of pottery, metal ware, plant ash and a brine well were unearthed.

Cangzhou was an important base for salt production during various dynasties, Wang added.

The filter is the only intact one ever found in Hebei Province and it proves Cangzhou was historically a salt production base, Meng Jianhua, a cultural official in Haixing County said.

(Xinhua News Agency May 12, 2006)