The Twelve-Month Hexagram Verses of Xuan Hezi 玄和子十二月卦金诀

Originally attributed to Xuanhezi, who is suspected to be Zhang Taikong, a Taoist priest of the The Tang Dynasty.

Consisting of one volume, it is included in the Zhengyi Section of The Daozang. This text focuses on the firing temperature for night alchemy.

It correlates the Twelve Xiyao Trigrams (Trigrams of Waxing and Waning Yin-Yang) with the twelve months and twelve two-hour periods of the day. Based on the changes of Yin and Yang in the trigram lines and the transition of cold and heat, it determines the alchemy time and the advancement or retreat of the firing temperature. The entire text is divided into twelve sections. Each section first presents the trigram image, followed by a seven-character poem with detailed annotations explaining the connection between the trigram and the firing temperature. It is largely based on Zhouyi Cantong Qi (Commentaries on the I Ching as a Guide to the Unification of the Three), a foundational text of Taoism alchemy.