Pop-Its

June 30, 2004 9:32 AM

4thOfJulyFilter: How do Pop-Its work? What are those little rocks inside of them made of?
posted by JeffK to Science & Nature (7 answers total)

The paper ones burn rapidly but do not "pop" like when you drop them. I think that after burning, some of the "rocks" remain. That would suggest that the kenetic interaction between the flammable and nonflammable rocks is central to the operation of the pop-it.
posted by Kwantsar at 10:19 AM on June 30, 2004

I'm a somewhat retired amateur pyrotechnician, I'm assuming that "pop-its" refers to those little paper wrapped devices that explode when they're stepped on or thrown. The rock itself is just inert rock, maybe sand. The explosive part is silver fulminate. Fulminates are made from a reaction between a metal and a high concentration of nitric acid. They're pressure and shock sensitive and can be very dangerous. The pop-its contain very small amounts of the fulminate so they're safe.
posted by substrate at 10:46 AM on June 30, 2004

So the rock is just ballast then? Something to give them a bit of heft so you can throw them around?

That makes sense.

But! As any red-blooded kid knows, trying to combine multiple snap-cracks (which is what I recall them as) into a giant snap-crack capable of actually doing something interesting ,results in nothing at all. It just doesn't work.

How come?
posted by aladfar at 11:43 AM on June 30, 2004

Really? I've combined a whole box into one big package and gotten a nice big bang before. usually dumped them all out into a piece of tissue and then lobbed it at something, hard.
posted by Hackworth at 11:52 AM on June 30, 2004

I had some once that each grain made a Pop when droped hard.
posted by Goofyy at 1:17 PM on June 30, 2004

Hackworth: I tried the same thing more than once as a kid and never had any success. Perhaps I wasn't throwing the finished product hard enough. And I guess it's possible that different brands have different levels of the fulminate chemical that substrate mentioned above.

This must be explored further!
posted by aladfar at 2:53 AM on July 1, 2004

I looked up their manufacture in my big book 'o pyrotechnics and the fulminate is actually soaked into the rock. As for why they might not work after being disassembled and reassembled bigger, better and faster than before it might have to do with a couple of things. First, they don't like humidity. Improperly stored fulminates will eventually stop being fulminates. Second maybe a larger bag of sand ends up cushioning the compound enough to make it less sensitive.
posted by substrate at 5:45 AM on July 2, 2004