Canon of the Primal Alchemical Earth 太古土兑经

The compiler is unknown.

Judging from its content and writing style, it is believed to have been composed in the late Northern and Southern Dynasties or during the transition period between the Sui and Tang Dynasty.

Both the General Catalog of Chongwen Library and the Bibliography of Arts and Literature in Comprehensive Records of the Song Dynasty recorded a work titled "Tudui Secrets in Three Volumes", which is exactly the present book.

The version preserved in The Daozang consists of three volumes, included in the Methods category of the The Dongshen Section. This book elaborates on the methods of subduing the properties of metallic and mineral substances in External Alchemy and gold-lead transmutation. It first points out: "Tudui is the essence of heaven and earth, the numen of mountains and rivers"; Tudui is another name for metals and minerals, nurtured by the qi of Yin and Yang. Medicinal substances such as the five metals, four yellows, and eight minerals each possess the properties of Yin and Yang, and can subdue one another. Therefore, those who study the Dao must first distinguish metals and minerals, then examine furnace fire, thirdly understand medicinal properties, and fourthly master the art of subduing.

The book successively records more than ten methods of subduing metals and minerals, including the Method of Subduing Mercury, Hu Gangzi’s Method of Subduing Realgar, the Method of Subduing Cinnabar, the Method of Subduing Cinnabar with Stagnant Mercury, the Method of Subduing Wrought Iron, the Method of Refining Iron Essence, the Method of Subduing Tin, the Method of Transforming Yellow and White Substances into Medicinal Ingredients, Another Method of Subduing Mercury, the Method of Subduing Alum, the Method of Subduing Naphta, the Method of Volatilizing Magnetite, the Method of Subduing Sulfur, the Method of Preparing Geng (Metal), the Method of Subduing Fluid Beads, and the Method of Making Mysterious Yellow Ointment.

At the end of the book, there is an appendix titled Extracts on Metals and Minerals, divided into ten sections: Clarifying Sovereign and Minister Drugs, Clarifying Volatilization and Subduction, Clarifying Yin and Yang, Clarifying Hardness and Softness, Clarifying Floating and Sinking, Clarifying Similarities, Clarifying Antagonisms, Clarifying Nature and Numen, Clarifying Silver and Mercury, and Clarifying Yellow Sprout. It mainly discusses the changes in the properties of metallic and mineral medicines, namely their chemical reaction characteristics, the subduction between Yin and Yang, and their properties of similarity and antagonism.

The book also states: "Thus, after achieving the Dao, Master Zhang compiled these three volumes of sacred methods as techniques for relieving the suffering of the world and nurturing life." It can be inferred that the compiler of this book is precisely Master Zhang.