The Huashu (simplified Chinese: 化书; traditional Chinese: 化書; pinyin: Huàshū; Wade–Giles: Hua Shu), or The Book of Transformations, is a 930 CE Daoist classic about neidan "internal alchemy", psychological subjectivity, and spiritual transformation. In the description of Poul Andersen,
The Huashu is a unique philosophical work of the period of the Five Dynasties, which syncretizes elements of Taoist, Buddhist, and Confucian thought, and which has been noted in recent times for its scientific observations (for instance regarding optics and acoustics) and for its unusual emphasis on epistemological considerations. Its influence during the Song and subsequent dynasties was substantial, both within Taoist and Confucian metaphysics, and especially as foundation of alchemical thought. (2007:517-8)