The Importance Of Aqua Regia In Tudor Times

In addition to a few elements already identified, Tudor alchemists were also familiar with some solvents, although the exact formulations hadn't been identified yet.

Of these, the most important was definitely aqua regia, as this was the only one that could dissolve gold, which was considered absolute purity.This solution was prepared through a complicated process of various distillations to reach the final product.

Step 1 – Preparation Of Oil Of Vitriol

What is now known as one of the strongest mineral acids, highly concentrated solutions of sulphuric acid (oil of vitriol) were obtained by two subsequent distillations of naturally occurring green vitriol (iron sulphate, FeSO4). The first distillation produced a dark solution with an unpleasant odour caused by the presence of sulphur dioxide (SO2), but the second distillation yielded a odourless and colourless solution containing sulphurous acid (H2SO3), which would be converted to sulphuric acid (H2SO4) by oxidation in air.

FeSO4 --> Fe2(SO4)3+ 2 Fe2O3+ 3 SO2
SO2 + H2O --> H2SO3
H2SO3+ O2 --> H2SO4

References to this process start around the 13th century, in the works of Vincent de Beauvais and Albert Magnus, and it was widely used in most alchemical procedures.

Step 2 – Preparation Of Spirit Of Salt

This solution was produced by distillation of common salt (sodium chloride, NaCl) and oil of vitriol (sulphuric acid, H2SO4), producing corrosive hydrochloric acid (HCl).

H2SO4 + NaCl → NaHSO4 + HCl

Some historians date the development of this process to 800 AD by Geber, an Islamic alchemist. However, it wasn’t until Tudor times that recipes to produce this solution started to develop and featured prominently in many European alchemists' work.

Step 3 – Preparation Of Aqua Fortis

This "strong water", was made by distilling oil of vitriol (sulphuric acid, H2SO4) and saltpetre (potassium nitrate, KNO3), producing a highly corrosive solution of nitric acid (HNO3). It was used by Tudor alchemists to dissolve many metals, with the exception of gold. This principle is still used in acid gold testing methods done today.

H2SO4 + KNO3 → HNO3 + KSO4

Step 4 – Preparation Of Aqua Regia

Made by mixing one part aqua fortis (nitric acid) and three to four parts spirit of salt (hydrochloric acid). The first reference to this solution, as well as aqua fortis, dates back to the 14th century, unfortunately by an unknown European alchemist writing under the name Geber (a famous 8th century Islamic alchemist). At the time, this was considered an absolute solvent, as no known chemical would withstand it. Currently chemists have identified some elements that are not corroded, such as osmium, rhodium, titanium and others; and the pursuit for an absolute solvent continues.