Video: Demo: How to make gunpowder explode
Gunpowder was a favourite toy of early scientific experimenters. So we were keen to see the enigmatic explosive in action in a replica 17th-century test rig
Behind an anonymous door at the bottom of a multistorey car park in the north of England, I am politely asked to surrender my phone and submit my bag for searching. I am reminded that my video camera should be used to record only the agreed subject of my visit – and not doors or entranceways, under any circumstances.
Once I am through an airport-style security arch and another set of secure doors, the reason for the wariness becomes clear. I am standing in a vast, windowless underground storeroom, its walls and shelves stacked with thousands upon thousands of guns.
Advertisement
This is the UK’s National Firearms Centre. Imposing as its repositories are, they are not why I am here. Guns mean gunpowder, and I am due on the centre’s firing range to witness an attempt to reproduce experiments from over three centuries ago, aiming to find out exactly how gunpowder worked.
Unexpected bangs
The tests are the baby of Haileigh Robertson, a PhD student in the history of science at the University of York, UK. Unnervingly, she admits she is not entirely sure how they will pan out. What’s certain is that if there are to be any large bangs, this would be a very good place to keep them quiet.
Gunpowder, a mixture of charcoal (carbon), sulphur and saltpetre (potassium nitrate), was discovered in 9th-century China, and spread steadily westwards over the following centuries. By the 17th century, its use in cannons and muskets was well established in Europe. But no one quite grasped how it worked. “It was a substance that everyone knew and appreciated. It was incredibly powerful and useful and in very high demand, but at the same time we didn’t really understand it,” says Robertson. “It was often referred to as magic.”
Even the process of making the stuff was steeped in mysticism. Saltpetre was often sourced from residues in animal dung, and there was little in the way of quality control. One batch might give a big bang for your buck, the next barely a whimper.
This was where gunpowder encountered the verve of the first experimental scientists of the Age of Enlightenment. Their mantra was “knowledge is power”, and there was no more obvious thing to test that on than gunpowder. Starting in the 1660s, a series of experiments under the aegis of London’s newly established Royal Society began. Gunpowder became a proving ground for emerging ideas about combustion and matter itself – the beginnings of chemistry as we know it. Better control over how gunpowder worked would, it was hoped, lead to its exploitation beyond the military realm.
Contemporary accounts of these experiments do exist, but are frustratingly incomplete. “Documents often only tell us about experiments that work, not about the challenges,” says Robertson. The Royal Society records do show that their testing apparatus, a device called an eprouvette, kept on breaking, sometimes because the experimenters put too much gunpowder in it. But really getting to grips with how these experiments worked means getting your hands dirty.
Testing time
Today Robertson is aiming to repeat the eprouvette work using a replica device built by historian Steven Walton of Michigan Technological University in Houghton. It has two vertical supports about 60 centimetres high, with a post suspended between them. Attached to the bottom of the post is a brass lid which sits atop a small powder chamber and priming pan.
When gunpowder is ignited in the powder chamber, the force of the explosion should propel the brass lid and post up past a series of ratchets that flip up, and then catch the lid as it begins to fall. The height the lid reaches is a measure of the gunpowder’s relative potency.
Igniting modern gunpowder in an eprouvette – the height of the ratchet indicates the gunpowder’s potency
Robertson’s collaborator Peter Smithurst, an emeritus curator of firearms at the National Firearms Centre, first packs the chamber with modern “black powder”. Technician Trevor Weston approaches cautiously with a long lit taper. I stand ready with the video camera. “I wouldn’t want to stand too close,” says Robertson, “until we know what it does.”
What it does, besides make an almighty flash and bang, is hard to discern at first. But when the smoke disperses, the lid is balancing 13 rachets up, half a metre off the floor. So far, so good.
“What it does, besides make an almighty flash and bang, is hard to discern at first”
Less successful are gunpowder mixtures prepared using old recipes by Smithurst, a trained chemist. There is the odd fizzer like a Roman candle, and quite a few proverbial flashes in the pan. No one is sure why these mixtures don’t work as well – perhaps the modern stuff is finer-grained, with a larger surface area to encourage ignition. Or maybe the samples have got damp somehow.
Archaeologists and historians alike want to understand the factors affecting the potency of early gunpowder. The power and range of early guns depended on the energy it could generate, so gunpowder influenced not only the design of cannons and armour, but also the evolution of battlefield tactics.
By reproducing these experiments we get a feel for what was possible – and an idea of the frustrations. Historically, we know gunpowder research was a slow burner: investigations of its action became a regular feature of the Royal Society’s house journal, Philosophical Transactions, during the 18th century.
Sadly, after a few more whimpers rather than bangs, I have to leave the firing range. On returning to London, I find an email from Robertson: drilling a larger borehole from the priming pan to the powder chamber had done the trick for the vintage powder formulations. Had the historical greats still been around, they might have been able to tip us off about that. But by doing things as they themselves did, we can at least meet them halfway.
Read more: “Reliving five eureka moments lost in history“
This article appeared in print under the headline “Blasts from the past”
