Commentary on Yin Zhenjun's Song of Returning Elixir 阴真君还丹歌注

Yin Zhenjun, also known as Yin Changsheng, was a figure from the Han Dynasty. Commentary on Yin Zhenjun's Song of Returning Elixir is signed as "Annotated by Xiyi Chen Tuan". It is included in Volume 35 of Yunji Qiqian (Seven Slips of a Cloudy Satchel) and in the Yujue (Jade Interpretations) category of the Dongshen (Spirit Grotto) section in the Daozang (Taoist Canon).

Chen Tuan was a Taoist priest during the Five Dynasties and early Song Dynasty. His courtesy name was Tunan, and he styled himself Fuyaozi. Historical records note that Chen Tuan was skilled in sleeping, "often staying asleep for more than a hundred days without waking up". He was known as the "Sleeping Immortal" and revered as "Ancestor Chen Tuan" in Taoism and among the people.

Chen Tuan had a passion for the I Ching. He created the Wuji Tu (Diagram of the Ultimate of Nothingness) and Xiantian Tu (Diagram of Innate Principles); it is also said that Zhou Dunyi's Taiji Tushuo (Explanation of the Diagram of the Supreme Ultimate) evolved from the Wuji Tu. Chen Tuan believed that all things are unified and there exists a "grand principle", which was later elaborated by Zhou Dunyi, Shao Yong, Zhu Xi, and others, becoming part of Neo-Confucianism in the Song Dynasty. Zhu Xi particularly admired Chen Tuan, once saying: "Thus, I am a direct descendant of Xiyi, and I truly rejoice in this." The modern scholar Meng Wentong commented on Chen Tuan: "Tunan was not merely a hermit, but indeed erudite and versatile; not merely a scholar, but inherently possessing heroic strategies. Could he be a dragon among men? When he lay high on the mountain peaks, the morality and literature of the two Song dynasties were already tied to him."

The Song of Returning Elixir consists of 33 lines, divided into four layers. The first layer talks about the unity of the River Chariot and golden sand, the 朱雀 (Vermilion Bird) regulating and nurturing the golden flower, and the golden flower generating the treasures of heaven and earth. The second layer discusses the correspondence between the dragon and tiger with the heavenly stems and earthly branches, the Eight Trigrams, and the Yellow River Diagram, stating that there are specific times for collection. The third layer focuses on setting up the furnace and tripod. The fourth layer expounds on true mercury and true cinnabar.

Chen Tuan's works on inner alchemy mainly focus on pure cultivation methods, while also involving human-origin yin-yang. His methods hold that the medicine of the great elixir is the genuine qi of the five elements. Humans should identify true yin and true yang to refine the elixir. One should collect the water from the Jade Spring in the upper dantian, refine it with the fire of the heart, and then send it to the lower dantian for elixir refinement; collect the primordial qi from the lower part and circulate it to the upper origin. The body and mouth are regarded as the furnace, the internal organs as the stove, and the twelve palaces in the body as the tripod vessels. The so-called "warming and nourishing" refers to keeping oneself free from joy and anger.

In his annotations, Chen Tuan criticized people for practicing outer alchemy, arguing that it is absurd to seek the great returning elixir by using five metals, eight stones, and various herbs. He also stated that "the great elixir requires no medicine". His alchemy methods are quite unique and exerted a certain influence on the theories and methods of inner alchemy in later generations.