In the latest episode of the BBC‘s Taboo, the enigmatic, masterful James Delaney (played by Tom Hardy) needs to get his hands on some gunpowder…and because he’s the enigmatic, masterful James Delaney (played by Tom Hardy), he promptly enlists scientist Dr George Cholmondeley (Tom Hollander) to make him some gunpowder.
The first step to producing the explosive substance, it transpires, is to find a substance called saltpetre.
Firstly, after paying a brief visit to Delaney’s farm, Cholmondeley lick-tests the manure of cows and chickens and offers the following advice:
“If you mix the pigeon s— and the chichen s— at a ratio of around 60:40 in favour of the pigeon…I’d have to do tests. And then if you burnt that stack of wood today, you could soak the ash in 50 gallons of human piss and leave it for a year and then, my friend, you would indeed have gunpowder.”
After Delaney expresses impatience with this plan, the pair agree to speed the process up by acquiring some saltpetre from the the warehouses of Delaney’s old enemy the East India Company.
But just what is Cholmondeley talking about? And would the grim-sounding process outlined above really help make gunpowder?
What is saltpetre? Do I need chickens?
Saltpetre or saltpeter, another name for potassium nitrate and a key component of gunpowder, is a chemical that can be produced naturally under certain rare conditions.
According to the website Today I Found Out, which has a helpful section on popular uses of urine, bat caves (real ones, rather than swanky Bruce Wayne hideouts) could sometimes be sources of saltpetre, thanks to the combination of a build up of bat poo and rock minerals.
In the absence of a handy bat cave, however, Cholmondeley’s method, time consuming as it sounds, would in fact be highly effective.
Give or take a few details, the method outlined on Survival Manual is very similar to an authentic nineteenth century recipe, detailed in an 1862 publication titled Instructions for the Manufacture of Saltpetre, written by an American named Joseph LeConte.
“To make the bed, a floor is prepared of clay, well rammed, so as to be impervious to water. An intimate mixture is then made of rotted manure, old mortar coarsely ground, or wood ashes (leached ashes will do), together with leaves, straw, small twigs, branches, &c. To give porosity to the mass, and a considerable quantity of common earth, if this has not been sufficiently added in the original manure-heap. The mixture is thrown somewhat lightly on the clay floor, so as to form a porous heap four or five feet high, six or seven wide, and fifteen feet long. The whole is then covered by a rough shed to protect from weather, and perhaps protected on the sides in some degree from winds. The heap is watered every week with the richest kinds of liquid manure, such as urine, dung-water, water of privies, cess-pools, drains, &c.”
But would it have to be human urine?
In contrast to what Taboo suggests, it seems that animal urine would also be effective: some traditional methods involved setting up the saltpetre bed under a barn, to ensure that waste water produced by cows would trickle directly through.
I’ve got some saltpetre! How do I turn it into gunpowder? And what makes gunpowder explosive?
We asked a chemist how to make gunpowder with saltpetre and he promptly replied with the following:”C + S + 4KNO3 > CO2 + SO2 + 4KNO2″.
In response to a request for some sort of clarification – “words, not just letters and numbers!” – he explained that the chemical formula above shows what happens when you mix potassium nitrate (saltpetre) with solid carbon (charcoal) and sulphur. Once the reaction has been started, it will generate heat, causing the potassium nitrate to release oxygen, which then burns the sulphur and carbon (provided by the charcoal).
The crucial explosive quality comes in because of the fact that, while solid carbon and charcoal take up comparatively little space, their gaseous forms take up much more space: “so within less than a second something that was happy taking up about 0.05 of a litre now wants to occupy a space 2000 times bigger”.