The oldest explosive substance is black powder. For the most part it consists of potassium nitrate (saltpeter), a nitrogen compound. In addition, it consists of charcoal and sulphur. In order to get saltpeter, the saltpeter refiners (Salpetersieder, Salpeterer) travelled from farmstead to farmstead with a writ of authority from the sovereign and and scratched the efflorescenced saltpeter off the walls of stables. In addition they had the right to dig up the soil of the stables and houses and to take along the soil containing saltpeter. Indeed the refiners were obliged to repair all damages, but did they always do their duty? There are often reports of strife. No one was happy when they showed up.

The saltpeter was tediously leached out of the soil, processed with the help of plant ashes and finally purified. Then it was filled into sacks or casks and brought to the collection point in the capital. With the Indian saltpeter trade and with the discovery of “Chile saltpeter” at the beginning of the 19th century, the job of the saltpeter refiner lost importance.


In order to get the saltpeter, the soil dug in the stables was mixed with plant ashes (potassium carbonate), shovelled into a large vat and drenched with hot water. The saltpeter was then dissolved by seepage water which soaked the soil. The developing brown slop had been drawn off by the refiner and clarified by mixing it with egg white that absorbed the impurities. Finally the saltpeter could crystallize.


Potassium nitrate is especially well suited for gunpowder because, in contrast to other types of saltpeter, it does not have the tendency to absorb water. In the stable soil, however, calcium nitrate is primarily found. The refiners mixed soil with plant ashes (potassium carbonate) and watered this mixture, and thus obtained the desired substance. They thought that the added plant ashes purified the saltpeter, because plant ashes were also otherwise used as a cleansing substance. In fact, however, the calcium nitrate (wall saltpeter) reacted in the cask with the potassium carbonate (plant ashes) to form potassium nitrate (saltpeter usable for gunpowder) and calcium carbonate (low solubility lime).


Because saltpeter is a product of bacteria, one can increase the saltpeter yield by feeding the bacteria. Since the Middle Ages, without knowing anything about bacteria, people set up saltpeter gardens. They mixed animal waste (feces, urine and blood) with soil containing lime, as well as with soil from cemeteries and slaughterhouses. This mixture was put into pits with lime, waste, and ashes or it was piled in mounds, covered, and, occasionally, liquid animal waste or urine was poured on it. After a year or two so much saltpeter had formed by disintegration that it could be washed out of the earth. However, the process was labor-intensive and expensive: most of the refiners preferred to travel from village to village to dig stable soil.


Pure nitric acid was called aqua fortis (Scheidewasser) because it dissolved silver and copper, but not gold. Metal mixtures and alloys could be separated (scheiden) by means of it. Aqua regia is a mixture of concentrated nitric acid with concentrated hydrochloric acid. The alchemists prepared it in the following manner: they mixed clay with table salt, forming little balls out of the mixture. These balls were roasted and hydrochloric acid appeared, the so called “spiritus salis”. If one roasted saltpeter in pottery shards, one would get the “spiritus nitri”, nitric acid. Both mixed give aqua regia – that has the capability to even dissolve gold.


In a alchemical tract of Basilius Valentinus published around 1600 the adept is instructed to take the “cold dragon / (that) has had his home in the stone cliffs for a long time / and in the caves to scrape the Earth in and out” (and to take this) set it on the “hellish seat”. This refers to wall saltpeter, that needs to be heated in order to produce nitric acid.

Why is the salt designated as a cold dragon? Because on the one hand it collects on cool, shaded walls. On the other hand, because it has the capability to make a fire flare up strongly - even though it is found in cool places.
Finally, nitric acid - being a corrosive, smoking liquid, that even “eats” copper with a dragon-sized appetite - can be made from the salt.


The alchemist Glauber (1604 – 1670) was enthusiastic about saltpeter. In his works he described it in a way that from today’s standpoint sounds visionary:
"These however all belong here / that the saltpeter in all things / as herbs / woods / four-footed and creeping animals / also birds in the air / and fish in the waters / as also in all elements / as earth / water / air and fire understood / so is he the true Spiritus Mundiuniversalis (universal fluid of the world) without which no life can be: he is a bearer and destroyer of all things / in him is all in all / which I with the age-old philosopher Hermete Trismigisto prove in my ‘Miracles of the World’ (Miraculi Mundi)."
This vision is confirmed from modern science in all particulars, only one must write instead of saltpeter the somewhat more general nitrogen.