This experiment started out as an attempt to make a mineral acid. Mineral acids are made from minerals such as green vitriol (Iron sulphate), saltpetre (potassium nitrate) and others. They were used by medieval alchemists to dissolve metals.
The origins of them are still a little unclear – I thought it likely, based on what I have read, that they were invented by Arabic alchemists some time in the 12/13th centuries AD, following in natural progression from the distillation of solutions of the minerals mentioned already. Others think they were invented by European Alchemists in the 13th century, especially in Spain.
One way to prove the argument one way or the other is to find an Arabic text which tells you how to make acids, from the right period. But the earliest definite recipe we have for nitric acid comes from a work of pseudo-geber, writing circa 1300AD in Europe, and thus not Arabic at all. It uses iron vitriol, saltpetre and alum, distilling them together to make nitric acid with some sulphuric acid from the alum.
One researcher, Ahmad Y. Al-Hassan, reckoned he had found an Arabic recipe. In a Liber Luminem Luminum, attributed to Michael Scot by historians in the 19th century, but probably not by him, there is a recipe which says (in the 19th century printed version): Continue reading