Ren Baqian became certain upon hearing Na Gu's words.
He had a flash of inspiration when he heard about the poisonous salt water. Even though it was poisonous, all things in this world were formed from ions and atoms and could, as such, undergo chemical reactions when subjected to the right conditions.
In other words, the salt could be extracted from the water, or the toxins could be removed.
Brine that was black and stank of rotten eggs was a kind of subterranean phenomena that could be found on Earth as well. About two thousand years ago, people from ancient times used their knowledge to extract salt from these subterranean brine sources.
This was the predecessor of the famous "well salt". Upon understanding more of how things worked in this world, Ren Baqian had gone back to find out more information about well salt. What he found was that salt could be harvested in places far from the sea, and that it was possible to obtain salt deep inland as well.
