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Xiaoxiao (Sodium Sulfate, refined) naturally grows in saline-alkali lands. Its appearance resembles fine salt. It dissolves immediately upon contact with water and can also digest various substances; hence it is called "Xiao" (Dissolving). Since this substance remains in its unrefined, original state, it is called "Pu" (Simple/Rough). All cattle and horse hides must be treated with this to become cured. In common parlance, it is also known as Yanxiao (Salt Niter) or Pixiao (Hide Niter). (*Zhi*) There are three grades of Xiao: that produced in Western Shu is called Chuanxiao (Sichuan Niter), which is of the highest quality; that from Hedong is called Yanxiao, which is second best; and that from Qing and Qi in Hebei is commonly called Tuxiao (Earth Niter). People in saline-alkali regions often scrape the soil, boil the juice, and let it stand overnight to crystallize. This still contains impurities like sand and dirt, appearing yellowish-white. *Bielu* states that yellow Pu Xiao harms people, while red Pu Xiao kills them. It must be re-boiled in water until dissolved, clarified to remove sediment, boiled together with several radishes until cooked, the radishes removed, and then poured into a basin. After standing overnight, it crystallizes into white Xiao, resembling ice or wax, thus called Penxiao (Basin Niter). The Xiao from Qi and Wei has much base material, with fine sharp crystals forming on top, which is what *Bielu* refers to as Mangxiao (Mirabilite). The Xiao from Chuan and Jin has less base, with crystal teeth forming on the surface like jade tablets, shaped into six-prism angles, transparent and lovely; this is what Li Shizhen (Jiamo) calls Mayaxiao (Horse-tooth Niter). Resembling white quartz, it is also named Yingxiao. The base precipitate of these two types of Xiao is collectively called Pu Xiao. By repeatedly boiling Mang Xiao and Ying Xiao with radishes to remove the salty taste, one obtains Tianxiao (Sweet Niter). (Used in *Zhongfeng Huoming Jindan*). Placing these two types of Xiao in wind and sun to evaporate moisture yields a light, white powder called Fenghuaxiao (Weathered Niter). Boiling Pu Xiao, Mang Xiao, and Ying Xiao together with Gancao (Licorice Root), followed by sublimation in a vessel, produces Yuanmingfen (Yuanming Powder). Scholars of the Tang and Song dynasties did not realize that all forms of Xiao are essentially the same substance, differing only in refinement; their speculative guesses were confused and lacked definitive guidance. (Li Shizhen)

The taste is bitter and salty. The nature is cold. It has slight toxicity. Pu Xiao settles at the bottom and is the coarse form of niter. Its texture is heavy and turbid. Mang Xiao and Yaxiao crystallize at the top and are the refined forms of niter. Their texture is clear and bright. Tianxiao and Fenghuaxiao are further processed from Mang and Ya Xiao, having had their pungent flavors removed, becoming sweet, mild, light, and refreshing. Therefore, Pu Xiao is only suitable for use on rough-skinned individuals or for external application/poultices. For decoctions or powders taken internally, Mang Xiao and Yaxiao are preferred. Zhang Zhongjing’s *Shanghan Lun* uses only Mang Xiao, not Pu Xiao, precisely due to this therapeutic indication. Its main action is not far from that of Mang Xiao. Only the conditions treated by Pu Xiao in *Benjing* are limited to the Six Fu Organs. However, since formulas like Chengqi Decoction entering the Stomach all utilize Mang Xiao, Pu Xiao need not be listed separately.