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Mercury (Shuiyin), produced in the flat lands of Fuling, is now sourced from Qinzhou, Shangzhou, Daozhou, and Shaowu Jun. The mercury from Qinzhou originates from the Western Qiang border region. The *Classic* states: "Mercury comes from cinnabar." This refers to mining coarse cinnabar from mountain rocks, placing it in a furnace, positioning water below, covering with an ang (a type of vessel), and applying heat externally. The fumes rise to the top, while mercury condenses and flows downward; its color is white and turbid. Tao Hongjing stated: "The mercury from Fuling's flat lands comes from within the cinnabar veins, or alternatively from sandy grounds, all being greenish-white." Such sources are no longer heard of today. As for that coming from the Western Qiang, locals also claim it is smelted in this manner. However, the mountains there produce it abundantly; some entire mountains naturally fracture, yielding large chunks of stone and sand the size of sheng or dou vessels, which must be crushed before smelting. Thus, mercury from the west is far more abundant than that from the south. According to the *Guangya*, mercury is called "gong" (mercury). Alchemists name it "gong"; the characters are generally interchangeable. The ash on the furnace lid is also called "fen" (calomel/mercurous chloride). Furthermore, mercury is sublimated to form calomel (Qingfen), which physicians use to purge stagnation in the diaphragm area and is considered a crucial medicine. Those who take it must avoid blood products because it originates from cinnabar.

Calomel (Shuiyinfen): See details under the entry for Mercury.

Realgar (Xionghuang), originally produced in the valleys of Wudu and on the southern slopes of Dunhuang Mountain, is now found in the mountains of Jiezhou. It occurs in lumps resembling cinnabar, clear and free of stone impurities; those with a color like a rooster's comb are genuine. Those that are dark green-black and hard are called Xunhuang (Smoked Realgar, pronunciation: xùn); those that resemble the genuine form in appearance but have a foul odor are called Chouhuang (Foul-smelling Realgar). Neither is used for internal administration; they are only suitable for treating sores and scabies. Washing them with vinegar eliminates the odor, allowing them to deceive the eye, so careful distinction is required when using them. Additionally, near the Western Rong border in Jiezhou, a type of "water-cave realgar" is produced, growing in rock crevices where springs flow. The host stones are named Qingyan Shi (Green Smoke Stone) and Baixian Shi (White Fresh Stone). Realgar emerges from these; the largest pieces are walnut-sized, the smallest millet-sized, with pores on the surface, deep red in color with a slight purple tint, extremely light and porous in texture, and more potent than ordinary realgar, making it highly valued by alchemists. Some say realgar is the "sprout" of gold; thus, it occasionally appears in the south near gold mines, though not as fine as that from the west. Records indicate realgar has been used to treat sores since ancient times. The *Rites of Zhou* records that surgeons treated sores using "five-poison medicines." Zheng Xuan's commentary notes: "Current medical formulas use five-poison drugs, prepared by mixing Huangdan (Red Lead, pronunciation: wǔ), Shidan (Cinnabar), Xionghuang (Realgar), Cishi (Magnetite), and Ci Shi (Magnetite), firing for three days and nights. The smoke deposits on the upper part, which is collected with a chicken feather and applied to the wound, causing necrotic flesh and broken bone to exit completely." Hanlin Academician Yang Yi often recorded that Yang, a young official at the Directorate of Historical Records, suffered from a facial sore that extended to the teeth and jaw, swelling like an inverted bowl, with continuous pus and blood discharge. The pain upon touching was unbearable, and despite various treatments over a year, it did not heal. Someone advised him to prepare medicine according to Zheng's method. After application, the necrotic bone and two teeth were expelled, and he healed immediately, thereafter remaining well. This confirms the rapid efficacy of ancient formulas. Huangdan (Red Lead) resembles the roof-tile-shaped cakes sold in markets today. In recent times, red lead tiles (Huangwa Ge) are still used in preparing alchemical pills, a practice derived from antiquity.