In a French book...

Capturing the Universal Spirit in an Undetermined State - Forums

alchemists are after a rare salt that chemically resembles NH4NO3 but has very different properties. When treated in the right way(by solve et coagula maybe?) it melts at 30°C and becomes blood red. The red color is the fruit of complex chemical reactions which are due to an important entropy.
He then writes that a friend of his let NH4NO3 deliquesce and recrystalize spontaniously for a period of 12 years and found that it took on an intense red color and that it's melting point was significantly reduced.
The red powder from dew can be carefully distilled and decomposes first giving an aromatic liquid, and then a red oil and leaves a charcoal like residue. From the latter one extracts a fixed salt. These three fractions are then purified and recombined like in the work on vitriols presented earlier in the book (dry distillation of an Iron sulfate similar to the lead acetate path) to give a stone which is refractory and has some transmutationary qualities. It is also an extraordinary remedy.

Then he writes that the dew can be used for the fermentation of metals because its salt is a soft oxydizer which is used during the slow calcination of minerals, a purifying operation which respects the subtle texture of the matter and is called 'assation' in french.
Mixed with another salt like the sal ammoniac, it constitutes the secret fire of the spagyricists of the past, an acidic salt which alters the matter so slowly that it presents the appearance of a putrefaction.