The Past of Nitric Acid: Water or Spirit?

Abstract

In the present review attention is paid to the complex and sometimes obscure names for HNO₃, particularly in alchemy, which often led to confusion because some of them were interchangeably used for different mineral acids. The names for HNO₃ are divided into three groups: names derived from the Aristotelian element water, those pointing to the origin from sal nitrum, potassium nitrate, and code words preferred by alchemists. HNO₃ became a problematic compound which seemed to exist in several variants. Two of them, aqua fortis and spiritus nitri, prepared in different ways, were distinguished as two forms of HNO₃ till the 18^th century. Modified preparations with added compounds of iron, arsenic, mercury and others were also described. In these cases, the final product was sometimes denoted aqua fortis; in alchemy the name aqua graduale was common. The rather complex mixtures were used in alchemy for attempted transmutation of metals. The review sums up the present state of knowledge, and turns attention to the questions that should be answered: more precise dating of the discovery of HNO₃ and of its form known as spiritus nitri. Alchemical recipes are a further problem: only rarely were they explained in terms of modern chemistry. A part of the review deals with attempts to reproduce the recipes under laboratory conditions, which could explain what reactions actually occurred. The history of HNO₃ thus calls for further research.