First jam jar

[larry cottrill]

I wouldn't put acetylene in it. I've seen a guy put a tiny squirt of acetylene in an upside down styrofoam cup, just hanging slightly over the edge of a bench. He then lights it with the tip of the oxy-act torch and the thing just blows into a million tiny little pieces with a massive BANG...if you did it with glass, I can see that being an long and expencive trip to intensive care getting 3000 little shards of glass removed from your face :D I could be wrong and maybe you need O2 for it, but still, I personally wouldn't do it. About 30% of the cups hole was exposed over the bench which is a very large area for the cup... still, it completely dissapeared!

The energy value of acetylene is enormous, and is usually underestimated by almost everyone, at least those who have little experience with it. A few years ago, my younger son was interested in doing things with a piezoelectric sparker from one of the little hand-held grill lighters. He found that he could add a little zip cord and make a "remote" sparker about 7 or 8 feet long. So, I carefully filled a small rubber balloon with a mixture of oxy and acetylene and plugged it with the spark gap, then wrapped it with wire to hold it. The filled balloon was only about 7 or 8 inches in diameter, since I didn't want to get a lot of pressure in there.

We set it off at a "safe" distance of 7 ft or so - as long as we could make the cord reach. It went off on the second try, creating a briliant yellow ball of flame a couple of feet across (obviously, "running rich"). The problem was, we hadn't imagined the need for hearing protection - the bang was so loud that it literally took 9 or 10 hours for our ears to stop ringing. And this was done out in the open, of course. I'll tell you, we were highly impressed with that one "little" bang!

A friend of my dad's was killed in his basement garage from an acetylene explosion that leveled his house. There was not much of him left to find in the rubble.

L Cottrill

[Mark]

"I wonder what size hole acetylene would work for in a very small jam jar? I wonder how fast it would run?"

Boy, I guess I frightened everyone with that remark. I can remember running my little Logan which volumetrically holds a little less than 70 ml total because I once filled the entire length with water just to see. And when I ran it on acetylene it would occasionally make a perky pop in starting.
Long ago I began to wonder if acetylene would run as a jam jar in a simple small straight tube of some length or at least some really unconfined shape, much less so than a typical jam jar aspect ratio because acetylene is so energetic.
I guess a good starting size would be about a 35 mm film canister size jar in metal with a larger than normal hole of course. That should be a good relatively safe size to try.
There might be some crossover from a jam jar to pulsejet because of the flame speed being so high, that is, the small jam jar might run as some sort of intermediate instead of putt-putting along.
Anyway, good point not to go trying acetylene in a real jam jar made of glass. I must remember that there are beginners out there! Thanks for the safety comments, I should have prefaced the acetylene topic at the top of the paragraph, acknowledging the hazards of C2H2.
Mark

[Mark]

I remember the one time I happened upon an explosive jam jar. It was a full sized ostrich egg made of paper mache, yes I bought it at an arts and crafts store. I drilled out a hole in the pointy end about a half inch in diameter and sprayed in some ordinary methanol. I was holding it with one hand and lighting it with the other. The paper wasn't thick enough I guess and when I went to light it, it went off with a really impressive bang. My fingers were stinging from this ostrich egg-bomb explosion.
It was amazing how perky methanol can be. I thought about buying another just because it made for such a good demonstration. Then I started to think about making my own with a balloon to hold the shape.
Impress your friends with exploding eggs. ha
Mark

[Irvine.J]

Yep, I've always wanted to strap an acetylene (and maybe an O2 tank with it) under a really large RC plane and drop it on my dads tinny at 200mph with a nice big fueltank on board. (possibly crashing the plane into it) Problem is, my dad isn't willing to sacrifice the tinny like that, but I believe it would a an honourable sinking!

I think the force/shock of simply dropping it should be enough to get it going.

[hagent]

I would also like to guess that the surface area of the bottom of the jam jar would also be a factor to some extent. The larger surface area the more fuel vapor available.

Also don't forget that acyetelen can decompose on it's own without oxygen. So filling up a metal jam jar may still be dangerous.


I almost had a jam jar explode on me just becuase I put a long snorkel on it. I'm going to guess it was around 24-36 inches. What happened when I dropped a wooden match down the tube was a very loud bang. My ears were ringing for a few minutes. I'm lucky the glass jar held.