Zao Fan

The drug is iron sulfate, chemically the same salt as the oral ferrous sulfate used worldwide for iron-deficiency anaemia, and its plausible traditional indications are the anaemia ones. Fe(II) is absorbed in the duodenum through DMT1 and exported by ferroportin under hepcidin control, which is why a single sizeable dose raises hepcidin and blunts absorption of the next dose for about 24 hours. Unabsorbed iron in the gut lumen causes the familiar nausea, epigastric pain, constipation and black stools, and blackens the teeth if the powder is held in the mouth.

Melanterite loses water of crystallisation on standing, so a stored sample drifts towards the tetrahydrate and monohydrate and the iron content per gram rises. The practical effect is modest but real: a gram of long-stored, powdery, partly dehydrated material carries more elemental iron than a gram of fresh crystals, so weight is not a stable proxy for dose.

Fe(II) oxidises to Fe(III) in air. This is the reverse of the toxicity problem seen in the arsenic and mercury minerals: oxidised material is less bioavailable, because Fe(III) is poorly absorbed compared with Fe(II), so a browned sample is a weaker iron source rather than a more dangerous one. Colour is therefore a rough freshness indicator, and yellow-brown material should not be assumed to deliver the labelled iron.

Melanterite belongs to an isostructural mineral group whose members are the copper, cobalt, manganese and zinc analogues of the same heptahydrate sulfate, so natural material routinely contains those metals in solid solution rather than as separable dirt. Copper is the one that matters: copper sulfate is itself a separate and toxic traditional drug, Dan Fan, and copper-rich melanterite shades towards blue-green, which is the same visual cue used to tell the two drugs apart.

Melanterite is a secondary mineral formed where pyrite oxidises, and pyrite commonly hosts arsenic and other trace elements which are carried into the sulfate efflorescence. The load is small compared with the arsenical and mercurial mineral drugs and should not be inflated into a comparable hazard, but it is the reason the general heavy-metal limits of the Chinese Pharmacopoeia (lead not more than 5 mg/kg, cadmium 1 mg/kg, arsenic 2 mg/kg, mercury 0.2 mg/kg, copper 20 mg/kg) matter for a mineral drug as much as for a plant one.

Calcining Zao Fan until it glows red produces Jiang Fan, also called Fan Hong, in which most of the iron has been converted to ferric oxide although sulfate remains. This is a distinct preparation with a different iron valence and therefore different absorption, and evidence about one form should not be imported into the other. Where a source does not say whether it means raw or calcined material, it should not be relied on for dosing.

Explains the name directly: green vitriol dyes cloth black, so it is called zao fan, soap vitriol. Li Shizhen warns in the same line that black vitriol also goes by the name zao fan and is not fit to be swallowed, being only for use on sores, and notes that the red material is commonly called fan hong to distinguish it from vermilion. He gives the drug as sour and cool and, unusually among the mineral drugs, classes it as non-toxic. He also records that heating it converts it to the red calcined form.

A green vitriol pill given for spleen earth weakness with exuberant liver wood overwhelming it, presenting as fullness of the heart and abdomen with a yellow swelling the colour of earth. That clinical picture, yellow puffy pallor with abdominal symptoms, is the classical huang pang bing, and in the parasite-endemic rice regions it corresponds closely to hookworm iron-deficiency anaemia. This is the one drug in this group where the traditional indication and the modern pharmacology genuinely converge, since the remedy is an iron salt and the illness was iron deficiency. It is recorded as a historical convergence, not as a treatment recommendation.

The governing modern standard, and the regulatory contrast with the rest of this group is the point. Zao Fan carries a full crude-drug monograph, sourced to the mineral melanterite and assayed at not less than 85.0 percent FeSO4·7H2O, with both a raw and a calcined processed form, and the compound preparation Fufang Zaofan Wan is separately listed as a pharmacopoeial patent medicine at number 1637. Unlike arsenolite, realgar, calomel and red mercuric oxide, Zao Fan does not appear among the 28 substances scheduled as toxic drugs under State Council Decree No. 23, nor among the nine minerals in Schedule 1 of the Hong Kong Chinese Medicine Ordinance. Its risks are those of any iron salt: gastrointestinal intolerance, interference with the absorption of other drugs, and acute overdose in children.