Sal Alembroth

Sal Alembroth was made by combining corrosive sublimate, mercuric chloride prepared by subliming mercury with vitriol and common salt, together with sal ammoniac, dissolving both in water and recrystallizing the mixture into clear, glassy, extremely corrosive crystals. The name alembroth is obscure in origin, possibly a corruption of an Arabic or a garbled alchemical coinage, and the honorific salt of wisdom or sal sapientiae attached to it in Latin texts reflects the esteem in which practitioners held its dissolving power rather than any claim to a literal philosophical meaning. It was used as a flux and menstruum in metallic work, valued for its ability to attack and combine with metals that resisted simpler acids, and it appears repeatedly in recipes attributed to or associated with the alchemist Basil Valentine and other writers working in the German and central European tradition of metallic alchemy.

Handling it required real caution given its mercury content, though early modern texts do not always dwell on the danger with the seriousness a modern reader would expect; mercuric chloride is severely toxic, and any preparation combining it with a volatile ammonium salt carries the hazards of both. Its reputation as a philosophical or spiritual salt, beyond its practical chemistry, likely owes something to the sheer difficulty and prestige of the combination it represented.

Sal Alembroth corresponds, in modern chemical terms, to a double salt or close combination of ammonium chloride, NH4Cl, and mercuric chloride, HgCl2, both individually unambiguous compounds whose combination is well attested in the historical recipes that survive. The precise crystalline structure that later chemists would call a true double salt, as opposed to a simple physical mixture of the two components recrystallized together, is not something every historical recipe specifies clearly enough to settle, and historians of alchemy including Lawrence Principe treat the exact nature of the combination as a secondary question next to the more important fact that both ingredients, and their general chemical behavior as a powerful and dangerous flux, are well documented.

Sal alembroth is a good example of a named alchemical preparation whose modern chemical identity is not seriously in doubt at the level of ingredients, even though the finer structural question of exactly how those ingredients were combined in any given batch cannot always be resolved from the text alone. The honorific name, salt of wisdom, is best read as a period judgment about the preparation's difficulty and usefulness, not as a claim this atlas repeats about any special property beyond its considerable, and considerably hazardous, chemical reactivity.