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-   -   starting a fire with a lemon (http://boards.straightdope.com/sdmb/showthread.php?t=790779)

blood63 04-18-2016 11:55 AM

starting a fire with a lemon
 
This video is a hoax.
I am embarrassed that I was duped into trying it.
I did get me thinking about how this could actually work.
With the right number of lemons are/or the right metals, could I actually start a fire?

Machine Elf 04-18-2016 12:01 PM

Yes, but you'll probably need a shitload of lemons and a shitload (each) of zinc and copper elecrodes. Each lemon one would serve as one battery cell capable of providing about 1 milliamp of current; you'd want to wire your lemons in parallel so as to provide a large current. Don't know how many amps is required to light off steel wool, but probably not much.

engineer_comp_geek 04-18-2016 12:19 PM

Sure. You'd need a lot of lemons.

The basic idea is there. The lemon battery is often demonstrated in basic science classes. All you need to make a battery is two dissimilar metals in an acidic electrolyte, so if you shove copper into one side of a lemon and zinc into the other, you've got a battery. It's a pretty weak battery, typically producing a bit less than a volt and current maybe around a milliamp or so. More surface area on your metal anode and cathode will give you more current.

Using steel wool to start a fire is also pretty well known. It is commonly done with 9 volt batteries. A 9 volt battery can put out a lot more current than a lemon battery though.

A table-top's worth of lemons tied in series-parallel strands should do the job easy enough.

blood63 04-18-2016 12:28 PM

Quote:

Originally Posted by engineer_comp_geek (Post 19269104)
Sure. You'd need a lot of lemons.

The basic idea is there. The lemon battery is often demonstrated in basic science classes. All you need to make a battery is two dissimilar metals in an acidic electrolyte, so if you shove copper into one side of a lemon and zinc into the other, you've got a battery. It's a pretty weak battery, typically producing a bit less than a volt and current maybe around a milliamp or so. More surface area on your metal anode and cathode will give you more current.

Using steel wool to start a fire is also pretty well known. It is commonly done with 9 volt batteries. A 9 volt battery can put out a lot more current than a lemon battery though.

A table-top's worth of lemons tied in series-parallel strands should do the job easy enough.

Or, instead of buying 20 or so lemons, I could slice each lemon into sections. Another video states that the electrodes will corrode very quickly in the acid and that I only have a limited amount of time before the current drops. Is this true?

engineer_comp_geek 04-18-2016 12:36 PM

Quote:

Originally Posted by blood63 (Post 19269134)
Or, instead of buying 20 or so lemons, I could slice each lemon into sections. Another video states that the electrodes will corrode very quickly in the acid and that I only have a limited amount of time before the current drops. Is this true?

That's true, but remember, thin slices and thin electrodes equals less current.

Quercus 04-18-2016 01:11 PM

Quote:

Originally Posted by blood63 (Post 19269134)
Or, instead of buying 20 or so lemons, I could slice each lemon into sections. Another video states that the electrodes will corrode very quickly in the acid and that I only have a limited amount of time before the current drops. Is this true?

It's true, but I'm not sure what 'limited' means in this case. Remember, the lemon isn't really doing much; mostly it's just sitting there passing electrons from one electrode to another (I think the acid may help a little bit, but that's not the most important thing). The metal electrodes are actually undergoing chemical reactions and being consumed by the reactions. So, yeah, the more current you run the more the electrodes will get used up (just like a non-rechargeable battery).

Qwakkeddup 04-18-2016 02:21 PM

Cave Johnson, inventor of the combustible lemon.

Richox 04-18-2016 02:53 PM

extending beyond the steel wool, you could certainly use a few lemons and therefor a few milliamps to ignite a fire with other common materials. Several ignitable liquids which vaporize readily at low temperatures would require almost no ignition energy.

It's a bit less of a party trick given the inherent combustibility of these other materials, but if we can think of a substance with low ignition energy requirements that isn't commonly viewed as combustible we might have a useful party trick!

Perhaps you could use it to set off a mini explosion with sugar as the explosive agent?

Lucas Jackson 04-18-2016 03:09 PM

Wouldn't a Bic lighter be easier to carry than a lemon and all those nails in a northern survival situation?

;)

Blue Blistering Barnacle 04-18-2016 03:10 PM

Quote:

Originally Posted by Richox (Post 19269622)
extending beyond the steel wool, you could certainly use a few lemons and therefor a few milliamps to ignite a fire with other common materials. Several ignitable liquids which vaporize readily at low temperatures would require almost no ignition energy.

It's a bit less of a party trick given the inherent combustibility of these other materials, but if we can think of a substance with low ignition energy requirements that isn't commonly viewed as combustible we might have a useful party trick!

Perhaps you could use it to set off a mini explosion with sugar as the explosive agent?

The oil sprayed out when you squeeze an orange peel is combustible- maybe something could be MacGyver-ed from a lemon rind?

excavating (for a mind) 04-18-2016 03:13 PM

I am curious why the OP thinks the video is a hoax and why subsequent posters think you would need a crapton of lemons. In the video, he uses 6 cells, stating it would produce "about 5 volts". As has been noted, it isn't only the voltage, but the amps that are important, but the amperage does not depend on the number of lemons, but the surface area of your electrodes. The brass paper brads he uses for the copper electrodes do have a lot of surface area.

If anything was "hoaxed" in the video, my bet would be that he injected a bit of HCl and water into the lemon just to make sure he had enough acidic electrolyte, but I am not sure that would even be necessary. He does squash the lemon a bit to make sure there is free flow of the electrolyte and cautions against letting the electrodes touch one another. I would really like someone explain why you would need a table full of lemons.

engineer_comp_geek 04-18-2016 03:24 PM

I haven't actually tried it myself, but my gut feeling is that the electrodes in the video are too small to produce enough current to heat up the steel wool to the point of creating flames. We're talking milliamps at about 4 or 5 volts, which ain't a whole lot of heat power.

Chronos 04-18-2016 03:32 PM

The biggest issue I can see with the demonstration in the video is that you need the steel wool to be the highest-resistance part of the circuit. But with the cells wired together with wires just loosely hooked onto the electrodes, I don't expect that's likely to be the case.

Count Blucher 04-18-2016 03:47 PM

...

blood63 04-18-2016 04:18 PM

Quote:

Originally Posted by excavating (for a mind) (Post 19269670)
I am curious why the OP thinks the video is a hoax and why subsequent posters think you would need a crapton of lemons. In the video, he uses 6 cells, stating it would produce "about 5 volts". As has been noted, it isn't only the voltage, but the amps that are important, but the amperage does not depend on the number of lemons, but the surface area of your electrodes. The brass paper brads he uses for the copper electrodes do have a lot of surface area.

If anything was "hoaxed" in the video, my bet would be that he injected a bit of HCl and water into the lemon just to make sure he had enough acidic electrolyte, but I am not sure that would even be necessary. He does squash the lemon a bit to make sure there is free flow of the electrolyte and cautions against letting the electrodes touch one another. I would really like someone explain why you would need a table full of lemons.

There is no way he produced six cells from a single lemon. How is he directing the charges inside the lemon? That is a single. The other electrodes are for show. Look how bright the steel wool gets. That's not possible.
I'm the OP, the one that got duped. I tested the voltages with my multimeter. A single electrode pair creates about 1 volt. Lining them up like they are in the video still makes one volt. It was fun to try and to play around with but there was no way it was going to work.

Walken After Midnight 04-18-2016 08:51 PM

Recent related thread: I burned my lower lip with lemon.

Walken After Midnight 04-18-2016 09:08 PM

They covered something similar on the programme Q.I., describing the use of lasagna to generate the electricity to power a gherkin lightbulb.

Machine Elf 04-18-2016 10:06 PM

Quote:

Originally Posted by excavating (for a mind) (Post 19269670)
The brass paper brads he uses for the copper electrodes do have a lot of surface area.

But the zinc nails (which are probably just galvanized steel) didn't have much area. You're right, it might be possible to do it with one lemon if you use a shitload of each electrode type so as to achieve high metal surfacea area, but it won't happen the way he wired it. He's created a single 0.7-volt cell between the two end electrodes that he attached his circuit wires to; all the intermediate electrodes aren't going to participate, and the two electrodes that do participate don't have much surface area, so the current capacity will be very limited.

If you used a bunch of each electrode type in one lemon, you'd need to connect all of the copper ones together to serve as one single electrode with large surface area; likewise with all the zinc nails. That would give you a single cell with about 0.7 volts and a decent current capacity.

It may be that 0.7 volts can't drive enough current through the steel wool, in which case you'll need to create another lemon cell just like the one above. Wire it in series with the first so you get 1.4 volts. still can't drive enough current? Add another cell. Keep at it until you have the voltage you need to get the steel wool hot enough to light; it's certainly less than 9 volts, and ISTR even doing it with a 6-volt lantern battery.

TL,DR: if you use electrodes with enough surface area in each lemon, it may be possible to do this with 12 lemons or less.

Senegoid 04-18-2016 10:11 PM

Quote:

Originally Posted by Walken After Midnight (Post 19270507)
Recent related thread: I burned my lower lip with lemon.

He might have mixed in some fresh field-ripened pineapple juice. You can use that for rocket fuel too.

furryman 04-19-2016 12:43 PM

When life gives you lemons, start a fire.

Really Not All That Bright 04-19-2016 01:55 PM

Quote:

Originally Posted by White SIFL (Post 19269660)
Wouldn't a Bic lighter be easier to carry than a lemon and all those nails in a northern survival situation?

Yeah, but the lighter won't save you from scurvy.

Irishman 04-20-2016 06:36 PM

Quote:

Originally Posted by blood63 (Post 19269876)
There is no way he produced six cells from a single lemon. How is he directing the charges inside the lemon? That is a single. The other electrodes are for show.

Correct. In order to make multiple cells out of one lemon, you need to isolate each pair of electrodes, i.e. slice the lemon. That way, the wires cross between slices.

The way it is shown, there is no way the series connected electrodes are contributing to the charge. With what is shown, each wired pair is a closed circuit.

Blue Blistering Barnacle 04-21-2016 06:09 AM

Quote:

Originally Posted by Irishman (Post 19275885)
Correct. In order to make multiple cells out of one lemon, you need to isolate each pair of electrodes, i.e. slice the lemon. That way, the wires cross between slices.



The way it is shown, there is no way the series connected electrodes are contributing to the charge. With what is shown, each wired pair is a closed circuit.


So, and I think this was stated upthread, if you take the same configuration as in the photo, drop the wires (and the attempt to link in series) you could connect the in parallel and get more current (with greater metal surface area) but low voltage. You could wire up several similar lemons in series to step up the voltage.

Blue Blistering Barnacle 04-21-2016 06:13 AM

I wonder if some distance would effectively isolate the nail pairs. Like, could you wire up nail pairs on opposite sides of a watermelon in series and get a step-up in voltage, or will the electrons "see" the nails on the other side of the melon.

Terminus Est 04-21-2016 06:41 AM

Rather than try to build a battery, it would probably be easier to squeeze the juice out of the lemon then use said juice to focus the sun's rays on some kindling.

DesertDog 04-21-2016 07:15 AM

MRE heaters use a powdered iron and magnesium alloy in salt water to create jillions of short-circuited galvanic cells that according to Wiki generate about 50 kilojoules. Having used them, I can attest they emit a strong ozone smell; any hydrogen is undetectable. It would be difficult to harness that to ignite steel wool, though.

Leo Bloom 04-21-2016 08:18 AM

How would additionally sugar and water affect the conduction? The lemon has some of one and a lot of the other. When life gives you lemons, then make lemonade, then fire.

Chronos 04-21-2016 08:29 AM

Quote:

Quoth Blue Blistering Barnacle:

I wonder if some distance would effectively isolate the nail pairs. Like, could you wire up nail pairs on opposite sides of a watermelon in series and get a step-up in voltage, or will the electrons "see" the nails on the other side of the melon.
Some, sure, but not very effectively. You'd need the internal resistance of the intervening fruit to be greater than the resistance of the rest of your circuit.

Blue Blistering Barnacle 04-21-2016 08:35 AM

Maybe I'll try it as a summer science project once kids are out of school.

Saint Cad 04-21-2016 08:48 AM

OK here's what I don't get about the video. Why is he wiring the zinc nails to the copper brads? What purpose is that supposed to serve?

Blue Blistering Barnacle 04-21-2016 09:06 AM

Quote:

Originally Posted by Saint Cad (Post 19277093)
OK here's what I don't get about the video. Why is he wiring the zinc nails to the copper brads? What purpose is that supposed to serve?


It's supposed to create a "series" of cells to step up the voltage (voltaic pile). But others have pointed out upthread that this will not be effective (because the cells are not isolated from each other). This video is felt to be a hoax by OP (who says he tried the experiment). Other posters agree for theoretical reasons.

Blue Blistering Barnacle 09-10-2016 08:04 PM

Still thinking of selling this idea as science project to my boy.

LunarPlexus 09-10-2016 08:17 PM

Does the Samsung Galaxy Note 7 qualify as a lemon yet?

Folly 09-10-2016 08:36 PM

After reading the comments, but before watching the video, I was wondering if the different segments of the lemon would offer any sort of isolating effect. But, the brads and nails aren't even going in the right direction in the demo for that.


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