Flutterby™! : things that go bang 2005-10-04 14:29:45.906723+00

things that go bang

2005-10-04 14:29:45.906723+00 by Dan Lyke 8 comments

Forest, my nephew who has been staying with us for a while now, has been asking about "things that blow up". I've been thinking about things that I can do fairly simply and easily that might be an introduction to learning, and that won't require me getting a safe to store materials when I'm not around to keep a watch on 'em. I've thought that one place to start would be with the old saltpeter and sugar smoke bombs (3 to 2 by weight, if I remember right). I should probably start by introducing the periodic table of the elements and going through the calculations necessary to come up with:

9.6 KNO₃ + C₁₂H₂₂O₁₁ --> 4.8 K₂CO₃ + 7.2 CO₂ + 11 H₂O + 4.8 N₂ (source)

Which is actually closer to 4:1. Huh, so much for the common lore, although maybe it's easy to melt the ingredients together with more sugar. Or maybe I should just check my sources better, as I haven't sat down with the periodic table and made sure that all works out.

From there I've been thinking about making black powder, but it sounds like to do a reasonable job at that I have to get a good unadulterated charcoal (ie: not briquettes), and build a ball mill, and... yeah, a damned lot of work. I've heard that sugar can be substituted for the charcoal, but I think it'd still require a ball mill (got the motor, could probably use a piece of PVC or ABS for the tumbler, would have to get some lead balls for the agitator, and spend a half a day fabricating the whole thing).

Unfortunately, he's a 12 year old product of the video game generation, zero attention span and all. If I were less burned out on him right now, and he had the attention span of, say, the rat boys, I'd go talk to the neighbors who have chickens, start by refining KNO₃ ourselves from that manure, probably just buy the sulfur outright, but... well... The other thing is that I'm not sure I trust him with this knowledge just yet.

So, anyone got any simple relatively safe ideas for things that go "bang" that don't require spending lots of time or too many tens of dollars at the chemical supply place? And it's been a long time since I've done my high school chemistry, anyone got a reliable source for the results of things like the classic KNO₃ + S + C and such so that if I do sit down with him and a periodic table of the elements and try to make this a reasonable lesson I don't have to do gobs of figuring? Especially sources that are more educationally oriented and less "Anarchist's Cookbook" like?

And, for the record 'cause maybe some day I'll be less burned out on him, and trust him a little more, here's a sugar rocket motor kit, building "waterfalls" and all sorts of other cool stuff from United Nuclear.

#Comment Re: made: 2005-10-04 16:23:10.458354+00 by: ebradway [edit history]

My Father always talked about a coffee-can, a handful of flour and a sparkplug... Let me see if I can find a source.

Another easy thing is to use some calcium carbide to generate some acetylene into a balloon and pop it with a match on the end of a stick. Nice fireball.

The great thing about the flour bomb, though, is that it teaches the principle that under the right conditions, just about anything can be enticed to go BOOM!

How about this as a Forest project? Nothing blows up, but I think it's still pretty amazing ---

Note that a perfectly proportional mix never yields ideal results, because of the granularity of the components, etc. You typically need to add more of one of the components (usually the oxidizer, but it can vary) to get an optimum effect. The lone exception to this rule is gaseous mixtures, such as butane/oxygen, because there's no granularity there. (The same may be true of liquid explosives, though I've never tried any.)

Cheat: walk into a gun supply store and purchase black powder, or even better.. Smokeless reloading powder. - Can you find such in your neck of the woods? How about cutting apart shotgun shells. Kewl stuff... and then you can play with the BB's as well.

I'd say twelve is a little young, but only because I was fourteen when I went through that phase and burned off my eyebrows more than once.

I'd also recommend steering clear of too much explosive "experimentation" because of the anti- terrorist fear present today. As a kid, playing with things that go boom (I grew up on a farm, and more than once we used them to clear stubborn stumps) was really cool, but even getting the ingredients today will raise flags.

That said, for source-books, "The Chemical Formulary" is a series that you may be able to find in a college library near you. I dug out dozens of different mixtures that I experimented with. It was published in the 30s or 40s, IIRC.

A friend with a similar history has been teaching his kids via model rocketry. That's probably a more socially-acceptable path today. There's a Zn-S rocket fuel I played with as a kid which worked pretty well, for example.

A little more edgy? Teach physics using medieval seige weapons. A small-scale ballista, trebuchet, etc., are all afternoon projects and can make a kid's eyes light up.

Shadow: the means for making the smoke (actually a lot of steam, I think) bombs involve melting the sugar, and at that point the resulting mixture is smooth enough that I think the KNO₃ is either dissolved or melted too. Not a perfect mixture, but a better mixture than you'd get with just the powders and a Dextrin or similar glue (what some sources recommend).

Meuon: That's what my dad did for me (at slightly younger than this, actually), but he's enough of an observer, not a doer, that I want to make this a more educational process. I also want to avoid having half a lb of black powder lying around, I'd much rather that, for security purposes, coming up with a reasonable amount of accellerant included some work.

And thanks for the warnings on sizes, I do have neighbors and windows... I should start with sand-sized grains and water balloons.

Dave: I don't trust him enough to play unsupervised, but I was blowing craters in the yard at his age (mostly with black powder, using tractor battery fired igniters made from multi-strand wire). One of the reasons that the various saltpetre based mixtures appealed was that (in my experience) low explosives have a much less threatening report. I've done the potato cannon thing with both propane (from hairspray) and starting ether as the propellant, and I've no idea if the risk of shrapnel from the latter is higher, but the report from it scares the daylights out of me.

I'll have to propose the trebuchet thing. I think he's too jaded. I'd also love to do the home-made rocket thing (I was thinking about starting with the two liter soda bottle pumped up to about 150PSI), but any proposal involving rocketry results in a "done that".