About the end of primary school I started to make gunpowder as any right-thinking child would want to. This meant getting hold of potassium nitrate, flowers of sulphur, and charcoal. It had to be potassium nitrate because the sodium salt absorbs water from the atmosphere. Down the ages soldiers have been warned to “keep their powder dry”. This was not for nothing, without the chemical accident that true saltpetre stays dry warfare would have been greatly delayed. In Durban road, not far from the end of Woodhouse rd was Dix’s chemist shop, Mr Dix clearly understood a young person’s need to make gunpowder and sold me large amounts of saltpetre and sulphur without batting an eyelid or asking any questions. I made the charcoal from dead dried-up sticks of bamboo. The bamboo was cut into pieces about six inches long and packed into a large old tin with a small hole in the press-on lid, the loaded tin was then put on a fire to cook. The volatiles from the bamboo were driven off out of the hole and burnt well in their own right. Once the volatiles were finished I let the tin cool until I could remove the charcoal and pack the tin for the next batch, I made and used a lot of charcoal! The brittle charcoal sticks needed to be crushed to a fine powder, I did this in another large tin. This second tin had a roller in it made from a glass honey jar filled with lead shot. By rolling the whole contraption the charcoal was rapidly reduced to a fine powder. This powder became electrostatically charged and could be stirred like a liquid, with all the particles repelling each other.
I must have found the proportions by weight in an old book “Fortunes in Formulas” although soon I could calculate them anyway. In modern times gunpowder is compressed hydraulically to improve contact between grains of the ingredients but I could not do this. Instead of compression I made the mixture slightly wet and then dried it gradually in a flat pan in our Moffat oven. I felt that this was what ovens were for , but my long-suffering mother did not. I was very careful and just used the warmth of a pre-warmed oven, no bright red elements! At this stage I had hard dry lumps of gunpowder which needed grinding down, again the tin with the lead-weighted roller came into use. I was careful about this and rolled the tin up and down a concrete path with my foot. I hoped that if the gunpowder ignited it would blow the lid off the tin and direct the blast sideways, this was an untested belief. I was not the only boy my age making gunpowder, but mine got a good reputation and I started to get orders. However after someone was careless and nearly burnt themselves I decided not to sell anymore, everyone else would have to make their own (the careless one survived and is now a professor in the USA).
The gunpowder was my basis for fireworks, guns, bombs and rockets. This version of gunpowder was not very good for making coloured flares, the colours of potassium and sodium overwhelmed most other tints, you really need potassium chlorate instead of saltpetre and Mr Dix did not supply such dangerous materials which can detonate much more easily.
We made guns out of electrical and water piping blocked at one end i.e. they were muzzle-loaders fired by a fuse through a small touch hole. When I think about how such piping is made I reckon we were lucky that none of our guns ever ripped open along a seam. At this time there were some rather pointless earthworks going on in the middle of the racecourse, they made an ideal firing range for guns and gave us something to blow up with bombs. On the edge of the racecourse was a large acacia tree (sieberiana), if it is still there then the one inch glass goen that we fired into its depths is also still there (could look on Google Earth, for the tree, not the marble!)
Bombs were often just a large water pipe screwed shut at one end and plugged shut with a deep layer of compressed newspaper. The pipe survived and the world was covered in paper confetti after a good bang. A variation was to put a compressed carbon dioxide cylinder , meant for making soda-water, into a tin filled with low-grade slow-burning gunpowder. The cylinders on heating split open with enough force to hurl bricks in all directions. Later on we experimented with ammonium nitrate and aluminium powder, but this is another more serious story.
A little bit of research into the history of rockets showed us that you do not just stuff powdered gunpowder into a tube, it will just blow up, not go up! The relatively loose powder allows the flash of flame to ignite all the powder almost at once. This is OK for guns and bombs but not for rockets. For rockets the powder must be compressed almost solid and there must be an open core down the centre of the charge, this way you get fast, but not explosive burning. The hollow core also protects the casing of the rocket from the hot gases until the last moment, otherwise cardboard rocket cases would never work.