The Cantongqi explains alchemy with the hexagrams of the Book of Changes.
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history
Attributed to 魏伯阳 of the Eastern Han, it is often called the oldest surviving book on alchemy. Its full title, Zhouyi Cantongqi, ties it to the 周易: it maps the heating of the furnace onto the hexagrams. Later Daoists read it as a guide to inner alchemy, refining the body instead of minerals.
mistakes
参 is read cān 'to join, compare' here, not shēn as in 人参 'ginseng'. The Tang Chan master 石头希迁 later gave the same title to a short poem on the unity of opposites, still chanted in Japanese Soto Zen temples as the Sandokai.
