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Also known as Wulongwei (Black Dragon's Tail) and Daoguan Chen (Inverted Hanging Dust). It is a substance formed by the condensation of smoke in the air. Its taste is pungent and bitter; the pungent flavor primarily dissipates nodules, while the bitter flavor primarily drains heat. Therefore, it treats abdominal pain, Yige (dysphagia), Yangdu Zhong'e (Yang toxicity in Cold Damage and sudden illness caused by evil miasma). Being light in texture and ascending in nature, it enters the Lung meridian to treat Houbi (sore throat with swelling and obstruction). Due to its pungent flavor which clears heat and its black color which enters the Blood level, it mainly treats Biyu (epistaxis) and soft sores on the head.

When using Liangshang Chen (Dust from Beams), one must select dust collected from places far away from fire and smoke, sift it, and then use it. It shows remarkable efficacy for sudden Zhong'e and persistent epistaxis. For Yangdu in Cold Damage presenting with macules (skin eruptions) and extreme restlessness and thirst, it produces immediate results. It treats internal abdominal pain and dysphagia, eliminates soft sores on the head, and is excellent when blown or applied locally for treating Houbi and Ru'e (tonsillitis). To treat Houbi and Ru'e, mix Wulonghei, Gufan (Alumen), and Zhuya Zaojia (Toothed Fruit of Chinese Tamarind) fried in salt until yellow, in equal parts, into a powder. Blowing it into the throat or applying it locally is both effective.

Dust and coal soot from old houses treat swollen gums with bleeding. Thus, dust from thatched roofs can cure chronic cough lasting many years.

This record comes from Su Song's *Tu Jing* (Illustrated Materia Medica), appended under the entry for Jiangshi (Ginger Stone). It is also recorded in *Bencao Jingshu*.

Maifanshi (Maifan Stone) is miraculously effective for treating Fabei Chuangdu (severe carbuncles on the back). Take this stone, crush it into pieces the size of chessmen, burn them red-hot in charcoal, and immerse them in rice vinegar for a long time. Repeat the process of burning and immersing ten times. Grind into an extremely fine powder like flying dust. Take one piece of deer horn, including the part connected to the skull, cut into segments of 2-3 cun. Burn in charcoal until no more smoke rises; this is called "Lianmo". Mix it with the stone powder in equal proportions, and double the amount of deer horn powder. Use three-year-old aged rice vinegar, place it in a silver or earthenware vessel, boil until bubbles resembling fish eyes appear. Then add the aforementioned powders, stirring constantly. Simmer for one to two shichen (4-8 hours) until the consistency is appropriate. Pour out and let cool. Apply the ointment to the swelling using a goose feather. Leave the surrounding red area intact, but leave the center of the swelling open to vent qi. If pus has not yet formed, it will resolve internally; if a head has formed, it will shrink; if already ulcerated, it will drain pus. If the disease has been prolonged causing muscle rotting and exposing bone/tendons, apply the ointment on fine cloth as a patch. Change when dry. The sore will converge daily. As long as there is no deep cavity remaining, it will heal completely. For already ulcerated sores, first wash with Pig Trotter Decoction to remove pus and blood, dry thoroughly, and then apply the medicine. One must strictly avoid touching the tender flesh with hands. Also, do not blow cold air with the mouth, nor should individuals with axillary odor, menstruating women, or pregnant women witness the preparation. These conditions are taboo during compounding. Initially, change the dressing once a day; after ten days, change it every two days. The medicine must be extremely fine to be effective; otherwise, application causes pain. If too old, it becomes ineffective. Prepare just before use. Grind until fine as flying dust. One or two liang can treat one carbuncle or furuncle.