The most noteworthy alchemy work in the Five Dynasties was Du Gutao's Fang Dan Jian Yuan. Du Gutao may be Persian. He updated and sorted out the book "The Origin of the Prescription Classic" in Tang Dynasty, and divided nearly 240 kinds of drugs into 25 articles, describing their shapes, images, medicinal properties, medical functions and uses of Dan medicine. This book was compiled shortly after Persian doctors and then alchemist Raz divided everything into three categories: animals, plants and minerals. Therefore, Du Gutao may have learned the classification of Raz from Persia, so he sorted out the disorderly "Fontaine Yuan Jing" and added some drugs, including items shipped from Persia to China, such as stone unicorn and salt green. (Peng-Yoke Ho: Collection of Daojing Prescriptions, published by Asia Research Center of HKU, 1980) It is also recorded in the book: "Purple alum, Persia, such as purple stone, can be turned into gold by silver and dried mercury."