Glauber's Salt

Glauber's Salt was first isolated and described in detail by the German-Dutch chymist Johann Rudolph Glauber around the 1620s to 1650s, who obtained it both from natural mineral spring water and as a byproduct of his own large scale preparation of hydrochloric and other mineral acids, where sodium sulfate forms when sulfuric acid reacts with common salt. Glauber recognized it as a distinct, previously undescribed salt, crystallizing from solution as large, colorless, transparent prisms that lost their water and crumbled to powder on exposure to dry air, a behavior called efflorescence that he documented carefully as one of the salt's defining properties. He promoted it energetically, publishing works that praised its medicinal virtues at length and gave it its enduring name, the wonderful or miraculous salt, sal mirabilis.

It entered pharmacy quickly as a mild purgative and remained a standard laxative salt for centuries afterward, sold well into the modern era under Glauber's own name. Because Glauber documented both the preparation and the properties of his salt in unusually careful published detail for the period, historians of chemistry treat it as one of the better attested individual discoveries in the whole history of early modern chemistry, in sharp contrast to substances whose origin is lost in an anonymous, centuries deep manuscript tradition.

Glauber's Salt is sodium sulfate decahydrate, Na2SO4.10H2O, an identification that rests on unusually solid historical ground because Glauber's own seventeenth century descriptions of its preparation, its crystal form, and its efflorescence behavior match the modern compound closely and because the salt has been in continuous documented use, under his name, from his own time to the present.

Unlike many entries in this atlas, there is essentially no scholarly debate to report here: the substance, its discoverer, and its approximate date of discovery are all matters of clear historical record rather than reconstruction from ambiguous medieval sources. What later chemistry added was an explanation for the efflorescence Glauber observed, the loss of water of crystallization to the surrounding air, and a precise account of why the decahydrate form is the one that crystallizes from cool aqueous solution while other hydration states form under different conditions, refinements that filled in the mechanism behind a substance Glauber had already characterized correctly by observation alone. Glauber's own confidence in the salt's medicinal value went well beyond what later medicine would confirm, a useful reminder that a chemically sound identification of a substance does not, by itself, validate every claim its original discoverer made on its behalf.