Mangxiao must be stored tightly sealed in a cool, dry place.
Pure Mangxiao crystals appear prismatic, rectangular, or irregularly shaped with uneven ends and varying sizes. They are white and transparent or off-white and translucent. Brittle and easily broken, they exhibit a glassy luster on fracture, are odorless, and have a salty taste.
Historical pharmacopoeias refer to it as "horse-tooth salt" (马牙硝), named for its crystalline resemblance to horse teeth. When naturally weathered or dried at high temperatures, mirabilite loses its crystalline structure and becomes a white powder known as weathered salt (风化硝), also called Xuanming powder (玄明粉). This form is also used medicinally, though its effects are milder than those of raw mirabilite.
Properties and Functions: This substance tastes salty with slight bitterness and has a cold nature. It enters the Stomach and Large Intestine meridians. Functions include purging, clearing heat, and softening hard masses. Indications include heat-induced constipation, abdominal distension and pain, masses and accumulations, abscesses, red eyes, mouth sores, and erysipelas.
Composition and Pharmacology Mangxiao contains hydrated sodium sulfate with trace amounts of sodium chloride, magnesium sulfate, and calcium sulfate. Xuemingfen contains anhydrous sodium sulfate. When ingested, sodium sulfate inhibits water absorption in the intestines, promotes intestinal peristalsis, and facilitates the passage of diluted stool.
Applications and Contraindications
For treating intestinal heat accumulation and constipation, it is often combined with rhubarb to promote bowel movements and clear heat. In cases of severe accumulation with abdominal distension and pain, it may be paired with zhi shi (Fructus Aurantii Immaturus) and hou po (Cortex Magnoliae Officinalis).For chronic constipation in the weak constitution, boil芒硝 with fresh radish until cooked, remove, then add fresh radish and boil again. Repeat 3–5 times. Consume the decoction to relieve constipation without harming the vital energy.Modern applications include combining this herb with Raphanus sativus seeds to treat adhesive intestinal obstruction, with Lysimachia christinae to treat gallstones, and with Artemisia capillaris to treat obstructive jaundice.
Topically, it clears heat and reduces swelling. For instance, apply externally to treat early-stage mastitis or breast swelling, hardness, and heat pain caused by milk stasis. Combined with rhubarb and garlic, add an appropriate amount of vinegar, pound into a paste, and apply externally for intestinal abscesses. For red, swollen, and painful eyes, dissolve an appropriate amount of芒硝 in 10 times its volume of boiling water for eye drops, or decoct and use the liquid for steaming and washing.For sore throat, mouth ulcers, or swollen, painful gums, mix芒硝 with borneol and borax into a powder and apply to affected areas.
Internal dosage: 10–15 grams, dissolved in herbal decoction or hot water. Avoid if stomach lacks real heat or intestines lack dry feces. Contraindicated for edema, elderly constipation, and pregnancy.