Some alchemical recipes, whilst appearing to be entirely practical on the surface, are probably not so underneath. One highlighted by Larry Principe in his “The secrets of alchemy”, is the sublimation of mercury with vitriol and saltpetre as carried out in 14th century Europe, from page 65:
“John first describes a series of sublimations of mercury with vitriol and saltpeter, followed by various digestions and distillations. Despite the apparently clear directions, however, his first step will not work in a modern laboratory if followed verbatim. The sublimate “white as snow” that John describes making is undoubteldy mercuric chloride; therefore, the starting mixture must have included common salt, but this substance is not mentioned in the list of ingredients. There are two possible explanations. First, John’s saltpeter might have been quite impure and contained a large quantity of common salt. In fact his De Confectione contains an annotation towards the end that notes how crude saltpeter ordinarily contains salt, and gives a method for purifying it by fractional crystallisation. The second possibility is that John intentionally left out the crucial ingredient as a way of preserving secrecy.”
Now, when laid out like that, it looks like there was a deliberate mistake, but then the question is also what mention of saltpetre and it’s purification is made in other alchemical works, especially those which John may have had access to? Continue reading