The History of Saltpeter - III

In our last post, we studied one of the techniques of producing saltpeter. We did promise there that we will study another method using niter beds. But, before we dive into that topic, let's cover a few more things that were left out in our previous post.

First, in case the reader is wondering, it is not possible to simply pick up a pile of fresh dung and urine and manufacture saltpeter that way. The dung and urine need to ferment for a while (at least 6 months or more), with sufficient moisture and shelter from rain and sun, and the soil needs to be alkaline and have certain compounds and not grow any crops on it.

Since we have the benefit of modern chemistry and biology knowledge, let us try to understand what is actually happening. First, when animals and people produce a large amount of urine and dung, under the right conditions, certain bacteria will turn the urea into ammonia and then combine that ammonia with oxygen in the air to produce nitrate ions. Now, these nitrate ions are looking to combine with other minerals. If the soil contains minerals such as calcium carbonate (limestone), magnesium carbonate or potassium carbonate, these minerals with react with the nitrate ions being produced by the bacteria, to form calcium nitrate, magnesium nitrate, potassium nitrate etc. Now if plants are allowed to start growing here, they will absorb the nitrates and grow tall and green, but there will be no saltpeter produced, since the plants use up the nitrates in the soil (nitrate compounds have been used as fertilizer for this reason). However, in stables, the animals will eat any plants and therefore, the nitrates can continue to form under the floorboards and walls of adjacent buildings. Similarly, if the ground is porous and dry, plants won't grow well and therefore nitrate crystals can form on it.

Now remember that we said that nitrates such as calcium nitrate, magnesium nitrate, potassium nitrate etc. are formed. Of these, only potassium nitrate is useful to us for gunpowder. The other two nitrates absorb too much water from the air and this reduces their explosive strength. The trick is to separate the potassium nitrate from the others. An Arab scientist from Syria named Hassan Al-Rammah described how to do so, in his book from 1270 AD titled "al-Furusiyya wa al-Manasib al-Harbiyya" (i.e. "The Book of Military Horsemanship and Ingenious War Devices"!) The details in his book seem to indicate that the method is of Chinese or Indian origin. The method described consists of dissolving all the nitrates in water and mixing in a lot of wood ash (which contains a lot of potassium in the form of potassium carbonate). The potassium ions in the wood ash replace the calcium and magnesium ions in calcium nitrate and magnesium nitrate and leave behind potassium nitrate, which can be crystallized. The knowledge of this method went westwards via the Italians and spread to the rest of Europe. A version of this method was described in the previous post.

All of this seems very obvious to us readers, who have had the benefit of knowledge passed to us by hundreds of scientists and inventors over many centuries. However, for people living in the 13th to 18th centuries, who did not have the knowledge of chemistry and biology that we do, the formation of saltpeter crystals was practically magic. They understood that decomposition of organic matter might have something to do with it, but they could not explain why saltpeter crystals would form under stables and cellars, but not in the open fields where dung is also found, and also why saltpeter crystals would not always form under stables if the weather conditions weren't right (the role of certain types of bacteria in the nitration process wasn't fully understood until the late 19th and early 20th century). The source of dung also had an effect on whether saltpeter was produced or not. While it was known that seabird guano was good for fertilizer, it wasn't as good for saltpeter production. However, some soil found under dove cotes (i.e. houses for pigeons and doves) was found pretty rich in nitrates. Stables provided with porous floors, such as straw and ashes, allow the formation of saltpeter. Some caves with limestone floors and filled with bats, would provide good saltpeter from the bat guano piles which were centuries old. Another puzzle was why sunlight and rain affected the production of saltpeter. Again, they didn't fully understand the roles of bacteria, soil chemistry, other minerals etc. This is why the role of the saltpeter men in various countries became so important, because people couldn't guarantee that saltpeter crystals would form at any particular location and it was left to saltpeter men to sniff around and find rich deposits of saltpeter. Since it was such a vital ingredient of gunpowder, they were given permission by their country's rulers to dig literally anywhere and given state protection from angry landowners.

In our next post, we will start looking into niter beds.

What is a Saltpeter Man?

Back in the early days of firearms, the propellant used was black powder. One of the components of black powder is a substance called saltpeter (or saltpetre, in British spelling). Saltpeter is more accurately known as potassium nitrate. Of the three main components of gunpowder, this one was the hardest to obtain in Europe, during the renaissance period. In fact, during the earliest years of gunpowder manufacture in Europe, no one was sure if saltpeter was a mineral that could be mined, or was it something that could be cultivated. The name comes from the Latin words, "Sal Petrae", which means "salt of rock", since it has the appearance of a layer of salt encrusted on rocks. Since saltpeter is white in color and since Europe during the early renaissance, got their saltpeter from Asia, it was often referred to as "Chinese snow".

A sample of saltpeter.

With the rise of gunpowder usage in various European kingdoms, it became necessary for governments to secure their sources of saltpeter. For instance, during the reign of Henry VIII in England, most of the saltpeter used for gunpowder manufacture in England was imported. Many countries realized that these supplies could easily be disrupted and therefore looked to produce it domestically. This gave rise to a specialized profession: saltpeter men.

Saltpeter men were people who were trained to extract saltpeter from nitrated earth (we will study this process in detail in subsequent posts). Since it was such a vital ingredient, saltpeter men were actually given special privileges by governments. For instance, in France, the saltpetermen were issued royal warrants by the king, called droit de fouille (translated as "the right to dig"), which allowed them to dig any soil that they suspected contained nitrates, without compensating the owners. In England, similar laws were enacted as well. In fact, in 1646, a new law was passed in the English parliament that allowed saltpetermen to dig in likely places and if any person refused to allow them to dig on their property, that person could be prosecuted by the courts! They were also allowed to demand carts belonging to other people, to be used to transport the saltpeter, and exempt from any taxes or tolls on any of the roadways in England. In theory, the owners of the land that the saltpetermen were digging, were to be compensated for any damage caused by digging, but often, the compensation amount was not enough to cover the damages caused. Saltpetermen were not a popular sight in many areas and many were either beaten up, or bribed by farmers to stay away from their land.

A man digging saltpeter earth in a barn.

Saltpetermen were allowed to dig practically anywhere, including palaces and churches, with the full protection of the British King and many a landowner dreaded the sight of saltpetermen walking in and tasting his soil. In one incident, saltpetermen walked into the church in Chipping Norton and ripped out the seats and tore up the floor, leaving no place for people to sit or kneel in church.

We will study more about saltpeter production in subsequent posts, but suffice it to say that quite a few countries had laws for barns and cellars to be built without flooring, so as to allow saltpeter to form in there. In America, in 1642, a law in Boston declared that "every plantation within this colony shall erect a house in length 20 or 30 foote, and 20 foote wide within one-half year next coming. &c., to make saltpeter." This law was actually based on a similar law passed by the King of England in 1626, that required citizens around London to do the same thing. Similar laws existed in Germany and Sweden as well. In fact, Swedish barns were not allowed to have paving stones until about 1830 or so and farmers were required to supply a certain amount of nitrated earth every year, as part of their taxes!

In the next series of posts, we will study the production of saltpeter throughout the centuries. I promise it will be a very interesting read.