Sciencemadness Discussion Board - Exploding Pumpkins

Exploding Pumpkins

annaandherdad - 21-10-2013 at 09:25

Not sure if this is the right section for this.

A couple of days ago some kids and adults and I exploded a pumpkin, using acetylene gas. We got the idea from the youtube video by mrhomescientist, in which he looked like he was having a lot of fun. We had fun, too.

We followed mrhomescientist in generating the acetylene by dropping lumps of CaC2 into a plastic container of water inside the pumpkin, but, unlike him, we ignited our gas with a high voltage spark. He used a hand-held lighter (butane, I think), inserted through a hole in the pumpkin, but I wanted us to be farther away from it when it exploded.

We made the high voltage with an old Model T spark coil. When I was a boy you could buy these things in auto supply stores (I got mine from the Pep Boys, circa 1962, and used it for all kinds of experimentation when I was a teenager). My old spark coil is long gone, but recently I ordered another one from ebay (not cheap, but I wanted one).

I had intended to use a standard auto spark plug , inserted through a hole in the pumpkin, to make the spark, but it turned out the shell of the pumpkin was too thick, so instead we made a makeshift spark gap. One electrode was created by a wire inserted inside a glass tube, which served as an insulator. We inserted the glass tube through a small hole in the pumpkin, with a short stretch of exposed copper wire sticking out on the inside of the pumpkin. We secured the wire to the glass tube at the other end with electrical tape. The second electrode was a nail stuck into the pumpkin itself, which made the spark gap with the exposed wire. Another nail inserted into the outside of the pumpkin was the other high voltage contact for the wires from the spark coil. At 10,000 volts, a pumpkin is a good conductor (the kids laughed when I told them that), and it carried the electricity well from one nail to the other. We set the spark coil itself near the pumpkin, and strung out 30 feet or so of low voltage wire to our command post, where we had the battery and a telegraph key to set the thing off. The kids got to press the key.

Like mrhomescientist, our basic idea was to cut out eyes and a mouth, then to put the pieces back in, so that when the gas went off it would blow those pieces out again. We got three ignitions. The first did a good job of blowing out the eyes and mouth with spectacular flames. The kids loved it. The second time we tried it were experimenting with waiting a longer time for more acetylene to accumulate. We must have let too much accumulate, so that there wasn't much oxygen left in the pumpkin, because when we set it off it made a soft whoosh, blowing out just one eye, when then belched a huge amount of black smoke and flame. I didn't want to breathe that smoke, I can imagine it wouldn't be good for you. On the third try we let the carbide fizz a shorter amount of time, and we got a really loud bang that blew out the eyes and mouth and most of the rest of the face of the pumpkin, too, blasting pieces of pumpkin out about 20 feet. Fortunately I have understanding neighbors.

It was a lot of fun, and educational on quite a few levels for the kids.

Acetylene makes good flames, but except for that I've been thinking hydrogen might be better. Acetylene is kind of nasty, especially when it burns incompletely. The pumpkin itself ended up covered with black carbon, that would get on your hands and was hard to wash off.

I had originally been thinking that if I wanted a really big bang, I could use a mixture of oxygen and acetylene (oxygen instead of air), but I'm glad we didn't try that because the last explosion (with air) was big enough.

Pickardjr - 21-10-2013 at 09:39

happy halloween.

confused - 21-10-2013 at 10:13

hydrogen would be good, but its alot lighter that air, so keeping it contained might be a problem, unless you can use hydrogen/oxygen filled balloons in the punpkins

MrHomeScientist - 21-10-2013 at 10:49

That's great to hear that I inspired some Halloween fun

I'm glad you took extra safety precautions too - I was always a bit nervous standing right behind mine! Nothing major yet, though I did blast a mouth-piece into an audience about 6 feet away once. Luckily it was moving slowly by the time it made it that far and only lightly bounced off someone wearing a heavily padded pumpkin costume! I always use only a few very small pieces of CaC₂ when I do my demonstrations to be on the safe side.
That's interesting that leaving it in for too long leads to a less forceful explosion - that definitely makes sense but I had never really thought about it. That could explain the poor performance I've gotten once or twice. Remember to store your carbide in an airtight container too. Mine was rather poorly stored in a ziploc bag inside a metal can, and has degraded significantly since I bought it.

In my neighborhood I'm actually known alternatively as "that scientist" or "the guy that blows up pumpkins"

maxpayne - 21-10-2013 at 15:48

In my neighborhood you would be known as "pumpkin head" or "pumpkin hater".

I really suggest you destroy something that you can create.

annaandherdad - 21-10-2013 at 16:08

mrhomescientist---sounds to me like a ziplock bag inside a can should keep out moisture pretty well---I just have the bottle the carbide came in, which had tape around the cap. As for the violence of the explosion, I was careful to get a pumpkin about the same size as the one I saw in your video, trusting that since you (apparently) hadn't killed anyone yet, I probably wouldn't either. Since the volume goes as the cube of the diameter, it would be easy to get a bigger explosion than expected.

Wikipedia says acetylene is not particularly toxic, but the commercial CaC2 often contains contaminants that generate H2S, PH3, AsH3 and other nasties. Certainly ours didn't smell too good.

When I was a boy you could buy calcium carbide in toy stores. It was used for cannons that used flint-steel sparks to set off the acetylene. Times have changed.

Lambda-Eyde - 21-10-2013 at 16:15

Quote: Originally posted by confused

hydrogen would be good, but its alot lighter that air, so keeping it contained might be a problem, unless you can use hydrogen/oxygen filled balloons in the punpkins

This isn't a really good idea - hydrogen/oxygen explosions are EXTREMELY powerful. A filled balloon with a perfect mix could easily make you go deaf under the right circumstances. A balloon filled with just H2 (and maybe a little air or oxygen) would be much better. IIRC Periodic Table of Videos has a clip showing the difference between the two (which is enormous).

elementcollector1 - 21-10-2013 at 16:24

Quote: Originally posted by Lambda-Eyde

Our science club did some experience with hydrogen-oxygen mixtures in balloons and remote detonators, and found that for a detonator of gunpowder on NiCr wire, the result was sadly disappointing. Methane was much more impressive.

On an unrelated tangent, a really fun demonstration that I encountered as part of a summer program for the University of Rochester was to bubble a tank of methane into soap, thus creating methane-filled bubbles. You would gather some of the bubbles in your hand, and someone would hold a match or lighter to the bubbles, causing your hands to erupt into flames for a fraction of a second. You wouldn't feel any pain, however, as the combustion was simply too quick (and your hands were already covered in wet soap).

[Edited on 10-22-2013 by elementcollector1]

Morgan - 21-10-2013 at 19:34

If you had a smooth pumpkin sans stem you could probably charge it up using a piece of PVC and paper towel sleeved over it much like rubbing fur on glass. Then you could make it spark discharge and ignite the interior as a variation on a theme. Or one might charge up a watermelon and have the watermelon ignite your pumpkin.
I know this sounds a bit odd but I experimented with several smooth fruits one day just out of curiosity. Smaller fruits such as a lemon won't hold as much charge. Below are some of the mildly interesting/quirky results. The other day I found the best round watermelon, it was a light green with dark green zigzag stripes which kind of reminded me of lightning bolts. I found a sheet of Teflon under the fruit made the best dielectric of all plastics I tried. The biggest spark with fruit was 9.5 inches long. If a wider sheet of Teflon were used you'd probably get even better results. The downside is it makes a lot of ozone when it fires and occasionally the charge can travel down the PVC to you if you get too close when charging. It's an outdoor and upwind experiment at best. I worry about the Teflon and PVC as they crackle when charging up, not good to breathe I'm sure.
http://www.youtube.com/watch?v=KRwVXnb5GUM
http://www.youtube.com/watch?v=0HlovqIMGkM
http://www.youtube.com/watch?v=P-NbshIOJmc
http://www.youtube.com/watch?v=Ne6L7wzV68Y
http://www.youtube.com/watch?v=UIFl5loB7Jo
http://www.youtube.com/watch?v=TgbNMTpyu88
http://www.youtube.com/watch?v=LW_UemdArW0

Here's where I came across the basic idea. It's so simple. All I did was use a longer piece of PVC tubing.
http://www.coe.ufrj.br/~acmq/foster.html

Random - 21-10-2013 at 20:48

Quote: Originally posted by Lambda-Eyde

Quote: Originally posted by confused

hydrogen would be good, but its alot lighter that air, so keeping it contained might be a problem, unless you can use hydrogen/oxygen filled balloons in the punpkins

True. There is one topic from me where I barely heard anything after I tried to make hydrogen gas burner in a glass jam jar.

DeadHead - 22-10-2013 at 06:20

Quote: Originally posted by annaandherdad

We made the high voltage with an old Model T spark coil. When I was a boy you could buy these things in auto supply stores (I got mine from the Pep Boys, circa 1962, and used it for all kinds of experimentation when I was a teenager). My old spark coil is long gone, but recently I ordered another one from ebay (not cheap, but I wanted one).

Just curious can you link me that ebay auction. I am an auto parts guy and feel I can find you coils that will do wonders for not too much money. I have personally ran a solid state tesla coil from a couple $12 ignition coils.

annaandherdad - 22-10-2013 at 09:56

Quote: Originally posted by elementcollector1

Do you mean the hydrogen didn't make much of a flame? That's what I was thinking, a hydrogen flame is nearly invisible, whereas acetylene makes a bright orange flame, from the carbon particles I assume. I assume also that methane or other hydrocarbons would do the same.

Morgan, thanks for the links to fruit electrostatics! They are very interesting. If I had seen these before we started, I might have worried more about an accidental ignition from an electrostatic spark. Maybe next time I'll keep the pumpkin wet to avoid that.

Deadhead, I just searched for Model T Spark Coil on ebay, there were several sellers with quite some range in prices. Many of the coils advertised were not in good condition, and several of the owners did not know if they worked (nor did they know how to test if they worked). I might have paid too much, but I got one in good condition and it does work.

Morgan - 22-10-2013 at 12:34

Tidbits on the static spark and source for buzz coil albeit expensive.
http://amasci.com/static/fostergen.html
Select Model T and then find coil in the part column.
http://www.vintageford.com/

[Edited on 22-10-2013 by Morgan]

annaandherdad - 22-10-2013 at 15:01

Yes, I see the coil for $95. That's what it looks like, a wooden box. I paid $75 for mine, as I recall.

When we were teenagers we did "experiments" like electrocuting roaches with our spark coil. I don't do that kind of stuff with the kids now, but we were boys.

BTW, Polverone has added Morgan's book, Simple Chemical Experiments, to the forum library.

Morgan - 23-10-2013 at 06:39

I bought two buzz coils from that company some years back and paid around 60 dollars for each. One was a little more money and instead of the wooden case it came in a black plastic. You could probably make your own without too much difficulty. There are several forums and ideas out there on the topic.
I damaged my wooden buzz box the other day turning on the power before have the electrodes in place. I think it arced internally. That's what you get for not paying attention. I might salvage the points and dismember an old lawnmower for a replacement magneto/coil. One time I used a car coil and long piece of all-thread and just raked a piece of metal over it creating beefy sparks from the make and break effect. I bet the first people to toy with this simple magnetic make/break feedback mechanism in the 1800's found it exciting. Now it's just another device.

I was watching this same show the other night and they had a different version using a laser but I found this other one which is illustrative too. Note the effect was perhaps more energetic than it needed to be.
http://www.youtube.com/watch?v=2-VCb9W3TIw

I'm glad Simple Chemical Experiments made it to the library.

watson.fawkes - 23-10-2013 at 09:55

Quote: Originally posted by Morgan

You could probably make your own without too much difficulty.

Well, it's not as simple as just winding a mess of wire around a core. Any inductor that gets a high potential across it needs proper internal insulation to resist internal arcing. It's off-topic here, and there are other places on the internet where folks who do this stuff hang out, such as 4hv.org.

Morgan - 23-10-2013 at 13:16

Here's something I was thinking I could use to "repair" my buzz coil, salvaging the points and mating them to a magneto coil. I could also use a car coil, somewhere I saw a design with the points atop it. It's neat how the electromagnetic effect of the coil pulls the points apart breaking the contact and then the spring arm, no longer being pulled down by the magnet makes contact again starting the process over and over. And it's such a tiny distance of travel.
If you have seen the direct ignition or COP (coil on plug) devices that sit directly above the spark plug, those are nice and small but expensive.
http://birkpetersens.blogspot.com/2013/01/buzz-coil-sparker_...

Morgan - 23-10-2013 at 18:39

As an aside and upon further examination, my wooden buzz coil merely suffered from a combination of the spring arm being bent from the device being packed away and a fleck of residue/corrosion on the points. Using a magnifying lens there was the tiniest amount of separation, a tiny amount of light indicating a gap between the points. I had been trying to start a Dynajet and didn't have alligator clips so the wires would accidently detach when I was hassling with the fueling and air so I thought I had somehow damaged it permanently because I heard a faint buzz and then nothing. I hadn't used it for a year or so.
I never did like the way the two points aligned when I got it but it worked so I didn't think anything of it. So now after filing the points and aligning them to seat fully and directly over one another, the baby is up and running, purring like a kitten and making ozone. I use a tiny wall transformer to run it, one I got off an old AT&T telephone that plugged into the wall.
A thought occurred to me that I might clip a few pieces of platinum off of one of my boats and perhaps make some longer lasting points. I had flattened one platinum boat out thinking I might use a piece of the metal in a homemade platinum catalyst lighter. My boats don't have a flange like this one but they're basically same only symmetrical.
http://www.youtube.com/watch?v=ikFZgP07GTE

[Edited on 24-10-2013 by Morgan]

Morgan - 26-10-2013 at 15:46

One time I took apart a common heavy black car coil and found a coil about as long as your index finger and only about an inch wide. All the rest of the volume was mineral oil I suppose. It looked ugly to me, wire wrapped around some opaque white plastic material, maybe some bobbin divisions. It was the cheapest the auto store had, made in Mexico for a cost of 6 dollars but with a nice outward appearance. Once apart, the coil itself almost looked like it was handmade with the leads dangling.

Tidbits on coil-on-plug ...

"Neodymium is used because it creates the strongest magnetic field when energized."

"The bobbins are designed from a fiber reinforced polyphenylene oxide glass material that has high
dielectric strength that prevents voltage flash-over"

"Standard’s secondary windings are manufactured with pure electrolytic tough pitch (ETP) fine (43 gauge) copper wire coated with a 180 degree Centigrade
coating. ETP is the finest wire for maximum voltage conductivity and the wire
coating provides a tough insulating jacket that prevents shorts under high heat
conditions."

"Engineered specifically to bond with the coil housing and bobbins, the high dielectric epoxy is injected into the case and is
pulled into a vacuum to eliminate any air pockets from forming within the coil. This insures long life by preventing moisture
intrusion or thermal breakdown caused by “air pockets” within the coil."

http://www.standardbrand.com/upload/Standard/Documents/Libra...

[Edited on 27-10-2013 by Morgan]

TheChemiKid - 30-10-2013 at 16:49

Just tried this out in my backyard. There was quite an explosion and it was quite loud. I have a video of it here: http://www.youtube.com/watch?v=ki1yRIjEh7o

Morgan - 21-11-2013 at 18:08

Quote: Originally posted by annaandherdad

Yes, I see the coil for $95. That's what it looks like, a wooden box. I paid $75 for mine, as I recall.

When we were teenagers we did "experiments" like electrocuting roaches with our spark coil. I don't do that kind of stuff with the kids now, but we were boys.

BTW, Polverone has added Morgan's book, Simple Chemical Experiments, to the forum library.

I came across another source for buzz coils and parts including the primary and secondary winding.
http://www.snydersantiqueauto.com/modeltparts/coilbox?page=3
A quirky device from the 1940's using a buzz coil.
http://www.youtube.com/watch?v=vBBHuJiSY6c
One of the more zippy buzz coil videos, perhaps run on 12 volts instead of the recommended 6. I remember having mine mounted underneath the top hollow beam of a metal sawhorse and the box arcing/shorting to the metal when the spark plug clip came off my Dynajet. It made a pretty impressive crackle.
http://www.youtube.com/watch?v=0QjPYMmhbVM

[Edited on 22-11-2013 by Morgan]

bfesser - 22-11-2013 at 07:40

<a href="https://www.sparkfun.com/products/11218" target="_blank">Spark Gap Igniter - 4.8V</a> <img src="../scipics/_ext.png" /> (SparkFun)

Morgan - 22-11-2013 at 16:15

Variations on a theme. Imagine these clunky things running day in, day out or for hours on end.
http://www.youtube.com/watch?v=evgetaarNHI
http://www.youtube.com/watch?v=zXqzOezr3aM
http://www.youtube.com/watch?v=xljX3ZA9Au8

Morgan - 22-11-2013 at 20:19

Quote: Originally posted by bfesser

<a href="https://www.sparkfun.com/products/11218" target="_blank">Spark Gap Igniter - 4.8V</a> <img src="../scipics/_ext.png" /> (SparkFun)

I was looking at several "high voltage pulse module" devices on eBay and they all had similar warning information about running time limits and arcing distance.
1. introduction:
Input: DC 3-7.2V, can be supported by batteries
Output: around 200KV
Input Current: 1-2A
High voltage arcing distance: 30-40mm
High voltage type: pulse current
Size: Φ25*68mm
Connection: positive end should be connected with the red wire, the negtive end should be connected with the other wire

2. notice when use it continuously:
The output end should not be without load for a long time
The power battery should be in a suitable distance with the high voltage wire
The arcing distance is proportional to both Battery capacity and Battery voltage
Provide enough current to get high voltage
Experimental test of the arc distance should go from short to long distance, if the distance is too long the energy can not be full release, the damage to the module may be made.

http://www.ebay.com/itm/DC-3-7-2V-6V-to-200KV-high-voltage-g...

The "100,000 volt units" I bought came with literature that stated
"Input: 2.4 VDC to 6VDC (0.5amp - 3.4amp draw)"
"Output: 100KVDC (3pps-69pps)"
"We tested them up to a 2" spark gap! We went over 2 inches and it did not arc internally. These are very well insulated against internal arcing and the driver circuit has over heat protection. We ran it on 6vdc for about 15 minutes, it overheated and auto-shut off. It came back on in a few minutes. Duty cycle was determined to be 100% at 2.4vdc input and 40% at 6vdc input. They get warm and require an aluminum sleeve heat sink with fins for cooling if you plan to use them at a high duty cycle ... to avoid over heating or damage from heat."
"Output is capacitive discharge via sealed spark gap inside module. Spark gap can be removed and SCR used for solid state switching and higher frequency output to emulate DC plasma. The modules can be used to make stun batons, stun guns, electric fences, force fields, etc... Can be used for charging high voltage capacitors or for ion or static field generation."
"Module is solid molded high voltage potted epoxy casted resin. Two sectons, bottom low voltage driver and upper tesla style high voltage pulse coil. White Mylar insulating tape is used to hold them together. That is where the hv spark gap is located to allow capacitive discharge of the bottom circuit into the high voltage induction coil."
"These are one of a kind."
Here's mine again for reference running on a small 3 volt battery. I just now ran it with 4 D batteries and a 2 inch gap which produced a faster fairly robust discharge. Still I have doubts about how long the device would hold up if I used it often.
http://www.youtube.com/watch?v=d33_Fhgy5Dg#t=32s

[Edited on 23-11-2013 by Morgan]

Morgan - 4-12-2013 at 18:45

I had my garage door opener replaced and found a flexible reed about 6 centimeters long with points inside the old unit with the electric motor. The two flat strips of metal vibrate like a tuning fork if plucked so I attached this arrangement to a car coil and small capacitor. Connected to a very fat spark plug about 2.5 cm in diameter and battery, the setup fires off a short-lived barrage of sparks as the plucked reed makes and breaks contact. The points have a small gap to start and the vibration fires the sparks.
Anyway, I was dwelling upon all the different ways to make and break a circuit as reed switches sometimes don't last as long as you would like. I came across this peculiar electrolytic interrupter with "a rapidity of from 200 to 1,700 times per second." "As the induced voltage in the coil depends upon the rate of interruption it is evident that this device will produce remarkably efficient results with any coil." Basically it's a tiny tip of exposed platinum wire adjacent a lead electrode in a dilute sulfuric acid solution. A bubble forms on the electrode breaking the circuit and then bursting with "remarkable rapidity". It's an impressive rate of resonance for so simple a device.
(Page 6)
http://books.google.com/books?id=e-hMAAAAMAAJ&pg=PA3#v=o...

In some way the above characteristic reminded me of the Leindenfrost effect. It might be possible to briefly drive a car coil using this same "effect" having a hot steel ball suspended by a thin quartz quartz tube with wire down the middle, submersed in a conducting solution. Instead of making and breaking a bubble formed by electrolysis, it would hypothetically be a make and break via stored heat. Perhaps with some thought, a long lasting bubble switch of some sort could be designed.
http://www.youtube.com/watch?v=FNh6LHRiFec

Here's one other device that could be useful to make and break a circuit if you could make it smaller and use less heat.
Trevelyan Rocker
http://www.youtube.com/watch?v=U23iwbVX-Dk
http://physics.kenyon.edu/EarlyApparatus/Acoustics/Trevelyan...
http://news.google.com/newspapers?nid=1499&dat=18880224&...

[Edited on 5-12-2013 by Morgan]

Morgan - 5-12-2013 at 19:33

Today I found a good example of a platinum anode and lead cathode in dilute sulfuric acid making and breaking a circuit over 1000 times a second, capable of producing ~50 centimeter sparks.
Large induction coil with Wehnelt interrupter
http://www.youtube.com/watch?v=m87-paje-ZI

[Edited on 6-12-2013 by Morgan]

Morgan - 12-12-2013 at 07:26

This old book entitled "The Theory, Design and Construction of Induction Coils" was published in 1908. Reading down through the pages I came across some interesting topics on interrupters, the state of the art for the time I guess as things evolved. Page 149 had a curious rectifier made with a lead and aluminum electrode using an alkaline phosphate. The simple platinum electrode Wehnelt interrupter is described with variations as well as the mercury Foucault interrupter seen in the third device presented in this video from Florence, Italy. Funny all the little properties and/or difficulties in design to overcome in the twenty or so pages on interrupters.

Induction coils (spark coils)
http://www.youtube.com/watch?v=btpFGpmAV0s

http://books.google.com/books?id=e0QOAAAAYAAJ&pg=PA128&a...

[Edited on 12-12-2013 by Morgan]

bismuthate - 12-12-2013 at 12:15

Now that christmas is coming who's up for exploding snowmen?!

Morgan - 13-12-2013 at 15:15

Here's an old device that might be amusing to make an ignition system out of. Be the first on your block. ha

"A special link could be included in the chain which incorporated an interrupter circuit. The purpose of the interrupter is to rapidly connect and disconnect the circuit so that the normally steady current of the battery is turned into a rapidly varying current. The usual practice in the use of medical electrical batteries was to feed the output of the interrupter to an induction coil in order to increase the voltage applied to the patient by transformer action. In Pulvermacher's patent however, there is no mention of using induction coils - the Pulvermacher battery could produce large voltages merely by adding more links to the chain. However, the interrupter still had an effect in that an interrupted current produces a stronger sensation of electric shock in the patient than a steady current."
"Even Bird, at the height of his dispute with the Pulvermacher company found himself able to say "the battery of Pulvermacher is an ingenious and useful source of electricity..."
http://en.wikipedia.org/wiki/Pulvermacher_chain

http://www.scienceantiques.com/Photos/pages/Pulvermachers-Ch...

[Edited on 14-12-2013 by Morgan]

Metacelsus - 13-12-2013 at 16:03

Quote: Originally posted by bismuthate

Now that christmas is coming who's up for exploding snowmen?!

I did that once a few years ago with 7.5 grams of flash powder, back in my kewlish days. It's a great way to piss off your neighbors!

Morgan - 13-12-2013 at 16:24

An ice bomb effect might be nice for a snowman.
"This demonstration is dangerous and the required equipment can be difficult to obtain."
http://www.youtube.com/watch?v=uE_fhooANhE

Maybe something like this thick aluminum Cuisinart bottle or a small steel CO2 paintball tank would fracture suddenly. I suppose though a tempered metal would be needed or work best. I wonder how small you could make an ice bomb? Imagine a cluster of tiny bombs in an acetone/dry ice bath going off like popcorn.
http://www.amazon.com/Cuisinart-SM4-CO2-Cartridge-4-Ounce-Re...

[Edited on 14-12-2013 by Morgan]

bismuthate - 14-12-2013 at 04:37

That would be absolutely amazing but I don't have experience in EMs so I shouldn't try that

. (hopefully next year).
Although I could make a chlorate/Ba(NO3)2/Al and another like it using St(NO3)2 and put it inside the snowman.