又名乌龙尾，倒挂尘。乃空中烟气结成。味辛而苦，辛主散结，苦主泄热，故治
腹痛噎膈，伤寒阳毒中恶也。体轻而上腾，故入肺而治喉痹，味辛而清热，色黑而入
血，故主鼻衄头上软疮也。
梁上尘，须远烟火处所，筛过方用，中恶卒来，鼻衄，流滴不已者殊功，伤寒阳毒
发斑，烦渴倍常者立效。主腹内疼噎，消头上软疮，喉痹乳蛾吹点皆妙。喉痹乳蛾，乌
龙尾、枯矾、猪牙皂荚，以盐炒黄等分，为末，或吹或点皆妙。
老屋尘煤，治齿龈肿出血，故茅屋上尘，多年咳嗽可除。
出自苏颂《图经》附于姜石条下。《本草经疏》载之。
麦饭石，治发背疮毒神效，取此石碎如棋子大，炭火烧赤，投米醋中，浸之良久，
又烧又浸。如此十次，研末极细，如飞尘，鹿角一枝，连脑骨者，二三寸截之，炭火
烧，令烟尽，即曰敛末，与石末等份，鹿角倍之，用三年米醋，入银石器内，煎令鱼目
沸，即下前药，不住手搅，熬一二时，稀稠得所，倾出待冷，以鹅翎拂膏于肿上。四围
赤处，中留肿头泄气。如未脓即内消，已作头即撮小，已溃即排脓，若病久肌肉烂，落
出见筋骨者，即涂细布上贴之。干即易，逐日疮收敛口，但中膈不穴者，即无不瘥。已
溃者，用时先以猪蹄汤，洗去脓血。挹干然后上药，其疮切忌手触动嫩肉，仍不可以口
吹阴风及腋气、月经孕妇见之，合药时，亦忌此等。初时一日一换，十日后二日一换，
此药要极细，方有效，若不细，涂之即痛也。 久亦无效，临用方锻， 过即研，细
若飞尘，一二两可治一痈疽矣。
又名乌龙尾、倒挂尘。这是由空中烟气凝结而成的物质。味道辛而苦，辛味主要能消散结滞，苦味主要能清泄热邪，因此用于治疗腹痛、噎膈（吞咽困难），以及伤寒阳毒和中恶（感受秽浊疫疠之气所致的急症）等病证。其质地轻扬而上行，故入肺经治疗喉痹（咽喉肿痛闭塞不通），因其味辛能清热，色黑能入血分，所以主治鼻衄（鼻出血）和头部的软疮（皮肤浅表化脓性感染）。
使用梁上尘时，必须选取远离烟火的地方采集，经过筛滤后才能使用。对于中恶突发、鼻衄不止的情况，疗效显著；对于伤寒阳毒引起的发斑（皮肤出现紫红色斑点）、烦躁口渴比平时更严重的情况，能立即见效。它能治疗腹内疼痛噎塞，消除头部的软疮，用于吹敷或点涂治疗喉痹和乳蛾（扁桃体炎）都非常巧妙。治疗喉痹和乳蛾，可用乌龙尾、枯矾、猪牙皂荚，用盐炒至黄色，各取等份，研成细末，无论是吹入咽喉还是点涂患处，效果都很好。
老屋的灰尘和煤烟灰，可以治疗牙龈肿胀出血，所以茅草屋顶上的灰尘，可以治愈多年的咳嗽。
这段记载出自苏颂的《图经》，附在姜石条目之下。《本草经疏》中也收录了它。
麦饭石，治疗发背疮毒（背部发生的严重痈疽）有神奇疗效。取这种石头敲碎如棋子大小，用炭火烧红，投入米醋中浸泡很久，再烧再浸。如此重复十次，研磨成极细的粉末，像飞尘一样。取鹿角一枝，连着脑骨部分，截取二三寸长，用炭火烧至烟尽，称为“敛末”，与石末等量，鹿角末加倍。用三年的陈米醋，放入银器或石器中，煎煮至液体沸腾冒出鱼眼般的小气泡，然后加入前面的药粉，不停地搅拌，熬煮一两个时辰，直到稠稀适度，倒出待冷却，用鹅毛蘸取药膏涂抹在肿胀处。四周发红的位置保留，中间留出肿头以泄气。如果尚未化脓，即可内消；如果已经形成脓头，可使脓头变小；如果已经溃破，即可排脓。如果病程长久导致肌肉腐烂脱落，露出筋骨，就将药膏涂在细布上贴敷。干了就更换，每天都能使疮口收敛愈合，只要中间没有空洞不愈，就没有治不好的。已经溃破的疮疡，用药前先以猪蹄汤清洗，洗去脓血，擦干后再上药。这种疮疡切忌用手触动嫩肉，也不可以用口吹阴风，腋臭者、月经期妇女、孕妇不要看到配药过程，配药时也要忌讳这些情况。初期一天换一次药，十日后两天换一次药。此药必须极细才有效，如果不细，涂抹时会疼痛。时间久了也无效，临用时才锻制，过后才研磨，细如飞尘，一两到二两就可以治疗一个痈疽了。
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.