Lawrence Principe - Secrets of Alchemy - Valentine's oil of antimony

Stibnite--roast (-sulphureous fumes)-->Ash--fuse--> Glass of Antimony --extract with vinegar (-inert dregs)-->Red Extract--extract with alcohol (-poisons)-->Sulphur of Antimony

A schematic of Valentine's chemical transformation of poisonous antimony into medicine. At each step, toxic or inactive materials are suposedly separated - an ilustration of the Paracelsian principle of Scheidung.

The most famous book in the Valentine corpus appeared in 1604 under the grand title of "The Triumphal Chariot of Antimony (Der Triumph-Wagen Antimonii)". [..] Valentine first describes a way to isolate the Sulfur of antimony. He begins by making "glass of antimony" (vitrum antimonii) - a vitreous substance used commonly (and perilously) to induce vomiting. He extracts the glass with vinegar to provide a red liquid, evaporates the liquid to a gummy residue, the extracts the residue with spirit of wine (alcohol) to give a sweet red oil. This oil is suposedly the Sulfur of antimony, and is no longer emetic or purgative because all poisonous qualities have been separated.

[...]Making the glass of antimony seemed a trivial preparation: this material appears commonly in early modern pharmacopoeia. Valentine even apologizes for starting with something so easy, but the initial results of replicating his procedure showed that the apology was unnecessary. Valentine instructs the reader to grind antimony ore (stibnite, native antimony sulfide), roast it slowly until it turns light gray, melt this "ash" in a crucible, and the pour out the molten material to provide "a beautiful, yellow, transparent glass". Accordingly, I took antimony sulfide and roasted it (laboriously, since it takes two or three hours of gentle heating and constant stirring, a process known as calcination) to a light gray "ash". This ash - predominantly antimony oxides - melted only with great difficulty, and when poured out solidified to a dirty gray lump. Many repeated attempts, with modifications to the temperature and duration of roasting and the length of time the ash was kept molten, always gave the same miserable result. After having exhausted other ideas, I obtained a sample of ore from Eastern Europe (Valentine specifies the use of "Hungarian antimony"), ground it, roasted it, fused the ash, all exactly as before - and this time obtained the beautiful, yellow, transparent glass.

What finally went right ? Analysis of the ore showed that it contained a small amount of quartz, one of the most common minerals on earth. This minute quantity, about 1 or 2 percent of the ore's total weight, proved to be the key; without its presence, the glass does not form. In fact, when i took the ugly gray lumps from the failed trials, remelted them, and added a pinch of powdered quartz (or silica, silicon dioxide), they also turned into beautiful golden glasses.

[...] Valentine next tells readers to powder the glass and extract it with vinegar to produce a red solution. Once again, theprocess failed. The yellow glass made with the addition of quartz gave no color to vinegar, even after weeks of stirring. The glass made from the ore gave only a pale reddish color after several days. Chemical analysis provided a surprise: this redness was due not to any antimony compound but rather to iron acetate, undoubtedly from trace amounts of iron in the ore. This red material was formed in such a small quantity that it seemed impossible for Valentine to have made as much of it as he claimed. This time the key lay in a disregarded detail in his recipe: Valentine writes that he stirred the roasting ore with an iron hook, and the stirred the molten glass with an iron rod. Antimony  compounds corrode iron very quickly. Thus, Valentine's iron tools enriched his glass with iron compounds. They provided the very substance he was isolating as the "Sulfur of antimony". Valentine's Sulfur of antimony actually contains nno antimony whatsoever; it was extracted not from the antimony but rather from his laboratory ustensils!

This amusing conclusion explains Valentine's claims and observations perfectly. Vinegar dissolves the iron out of the glass, but also dissolves some antimony compounds - hence, the vinegar extract still has the purgative properties Valentine noted. But after the vinegar solution is evaporated, and the gummy residue is extracted with spirit of wine, only the iron acetate disolves, leaving all the antimony behind in insoluble residues. As Valentine writes (correctly), "the residue that remains behind contains the poison, the extraction takes up only the medicine". The alcohol extract is completely nontoxic, and is, just as Valentine says, "sweet", for iron acetate has a slightly saccharine taste.