Chart of the Fire Phases The chart reproduced below comes from
the Yiwai biezhuan (The Separate Transmission of the Book of
Changes), written by Yu Yan in 1284. This work contains several
cosmological charts, followed by passages drawn from the Book of
Changes and commented by means of quotations from the Cantong qi
(The Seal of the Unity of the Three), the most important text in
Taoist alchemy. Charts like this one have a long history in
China. They are used to show the correspondences between
different ways of marking space and time, such as the
directions, the twelve primary hexagrams (each of which is
associated with one month), the days of the moon cycle, the
lunar mansions, and so forth. Different cosmological disciplines
use these charts in different ways e.g., for astronomical
calculation or divination. In alchemy, the correspondences shown
by these devices are mainly used to establish the "fire phases"
(huohou), i.e., the cycles of firing in external alchemy
(waidan) and the cycles of the circulation