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.