text: Interest in elixirs of immortality increased during the Han dynasty (206 BC–220 AD). Emperor Wu (156–87 BCE) employed many fangshi alchemists who claimed they could produce the legendary substance. The Book of Han says that around 133 BCE the fangshi Li Shaojun said to Emperor Wu, "Sacrifice to the stove [zao 竈] and you will be able to summon  things  [i.e. spirits]. Summon spirits and you will be able to change cinnabar powder into yellow gold. With this yellow gold you may make vessels to eat and drink out of. You will then increase your span of life. Having increased your span of life, you will be able to see the [xian 仙] of [Penglai] that is in the midst of the sea. Then you may perform the sacrifices feng [封] and shan [禅], and escape death".
  Wei Boyangs c. 142 Cantong qi', which is regarded as the oldest complete alchemical book extant in any culture, influenced developments in elixir alchemy. It listed mercury and lead as the prime ingredients for elixirs, which limited later potential experiments and resulted in numerous cases of poisoning. It is quite possible that "many of the most brilliant and creative alchemists fell victim to their own experiments by taking dangerous elixirs". There is a famous story about animal testing of elixirs by Wei Boyang. Wei entered the mountains to prepare the elixir of immortality, accompanied by three disciples, two of whom were skeptical. When the alchemy was completed he said, "Although the gold elixir is now accomplished we ought first to test it by feeding it to a white dog. If the dog can fly after taking it then it is edible for man; if the dog dies then it is not." The dog fell over and died, but Wei and his disciple Yu took the medicine and immediately died, after which the two cautious disciples fled. Wei and Yu later revived, rejoiced in their faith, took more of the elixir and became immortals.
  Elixir ingestion is first mentioned in the c. 81 BCE Discourses on Salt and Iron.