down the borehole. A membrane valve then captures the brine for retrieval on the surface. Once the brine is retrieved it's then piped to flat pans for boiling. In the boiling process some water and crushed yellow soybean is added. The soybean absorbs the impurities in the salt. Once boiled, a yellow layer is formed - this is scraped off leaving absolutely pure salt. The salt is a medium grain salt with different size flakes which have a very strong and unique salt taste. This salt has no additives so it does clump. Locals use grains of rice in the salt to keep the salt from clumping. Early methods of brine salt production involved digging large pits in the earth (other parts of China used the evaporation method). Later methods involved very innovative drilling and retrieval methods. An unexpected byproduct of the drilling and resulting wells was natural gas. Since natural gas didn't have the uses it does today, it was channeled into pipes and primarily used onsite to boil the brine and extract the salt. The salt Zigong produced was very rich in taste and was served to the Emperor of China as a tribute. The people of Zigong believe its taste to be superior to the popular French sea salts such as Fleur de sel. Salt production via boreholes was once prevalent in the entire Sichuan area - but for several factors (war, rebellion, taxes, wells drying up) Zigong became the center of production. Salt wells in Zigong were deeper and had better brine salinity - making for better yields in the salt extraction process. The method in which boreholes were drilled is significant. In 1835, the world's (at that time) deepest well was drilled reaching 3,300 feet. The miners of Zigong refined the techniques of deep borehole drilling. Later, Europeans copied and further refined the percussion drilling methods - so its effects can be seen in the modern Drilling rig used for oil and water. Salt became an engine of commerce and wealth for Zigong. There were cheaper methods for salt production, as to start a borehole well cost 3,000 pieces of silver, but transportation cost into the Sichuan valley negated the cheaper production methods (as they usually involved sea water). Zigong is located in the central Chinese Sichuan province, which was a large basin, surrounded by mountains on three sides and therefore somewhat isolated. Before refrigeration