Sending strong electric currents through seawater

[taybot]

Okay, cool. The word "net" just threw me off for a second.

 

[tiviny]

bit late, but perhaps a plot device could be a spear-gun like device that shoots an electrode attatched to an insulated cable? That way you might be able to get some range and accuracy, although I don't know how viable something like this would be. Reading this thread tells me I should take electronics classes.

 

[skeptic2]

For anything but short duration, I think it will have to be AC power. DC will cause the water to break down into its component gases around the electrodes, and this will severely hinder the current flow from the electrodes.

When I was a kid, I had a 24 V transformer that I used for all kinds of experiments. The secondary was not rectified. I put the wires connected to the secondary (AC) under water and underneath a small prescription pill bottle. Bubbles streamed off of both wires. When the bottle was about half full of gas I touched the two wires together creating a spark that sent the bottle bouncing off the ceiling and around the room.

I also tried electrolysis of salt water which makes sodium hydroxide and chlorine. The problem was that the chlorine reacted with everything I tried as an electrode. I tried copper, silver, nickle, aluminum, steel and graphite. Apparently there was a binder in the graphite that reacted with the chlorine and caused the graphite to pulverize. At the time I didn't think to try the carbon core of a battery. (Besides, my parents ended that experiment early after smelling a strong odor of chlorine throughout the house.)

 

[metiman]

You realize that what you are calling 'the smell of chlorine' was actually chlorine gas, used as a chemical weapon in WWI. It is highly corrosive and can cause permanent lung damage as well as death. If your parents hadn't 'ended the experiment' you might have all died or suffered permanent injury.

 

[NascentOxygen]

When I was a kid, I had a 24 V transformer that I used for all kinds of experiments. The secondary was not rectified. I put the wires connected to the secondary (AC) under water and underneath a small prescription pill bottle. Bubbles streamed off of both wires. When the bottle was about half full of gas I touched the two wires together creating a spark that sent the bottle bouncing off the ceiling and around the room.

You imply that AC was decomposing water. I think your recollection may not be complete. As for rocketing a pill bottle around the room, please forgive my skepticism here, too. I daresay in the scenario you paint, that little bottle would not lift even ¼ inch.

I also tried electrolysis of salt water which makes sodium hydroxide and chlorine. The problem was that the chlorine reacted with everything I tried as an electrode. I tried copper, silver, nickle, aluminum, steel and graphite. Apparently there was a binder in the graphite that reacted with the chlorine and caused the graphite to pulverize.

I, too, noted how my improvised carbon electrodes suffered erosion below the waterline, I put it down to the mechanical abrasion of the bubbles--not friction, but cavitation. As each bubble "explodes" into existence, a volume previously occupied by liquid expands instantly in volume by hundreds of times as it becomes gaseous. This fits my definition of an explosion, and it is occurring in the crevices of the carbon rod.

 

[jim hardy]

perhaps it was his toy train transformer which would have been equipped with a rectifier so the locomotive can be reversed ??

That'd be consistent with observed H2 pill bottle launch.

 

[skeptic2]

You realize that what you are calling 'the smell of chlorine' was actually chlorine gas, used as a chemical weapon in WWI. It is highly corrosive and can cause permanent lung damage as well as death. If your parents hadn't 'ended the experiment' you might have all died or suffered permanent injury.

When I said "the smell of chlorine" it was on the order of what you'd smell at an indoor swimming pool. This wasn't the first experiment I had done and my parents had learned to be extra cautious with my experiments. Usually I did them when they weren't home.

You imply that AC was decomposing water. I think your recollection may not be complete. As for rocketing a pill bottle around the room, please forgive my skepticism here, too. I daresay in the scenario you paint, that little bottle would not lift even ¼ inch.

If I implied that AC was decomposing water I'm sorry. I didn't mean to imply that. I meant to state it unequivocally. Is it difficult to believe that during a half cycle one wire is positive and the other negative so O2 will form on one wire and twice as much H2 forms on the other? During the next half cycle the process reverses. If you believe that a few mL of an ideal mixture of O2 and H2 won't send a pill bottle bouncing around the room, I urge you to try it.

I, too, noted how my improvised carbon electrodes suffered erosion below the waterline, I put it down to the mechanical abrasion of the bubbles--not friction, but cavitation. As each bubble "explodes" into existence, a volume previously occupied by liquid expands instantly in volume by hundreds of times as it becomes gaseous. This fits my definition of an explosion, and it is occurring in the crevices of the carbon rod.

You may be right. All I saw is that when I dipped my pencil lead electrode beneath the water, the graphite turned into very fine particles and floated to the surface.

perhaps it was his toy train transformer which would have been equipped with a rectifier so the locomotive can be reversed ??

That'd be consistent with observed H2 pill bottle launch.

Actually it was a doorbell transformer in an electrical box that kept the 120 VAC from being exposed. On the secondary side there were terminals for different voltages, but I always used it at 24 volts.

 

[jim hardy]

Hmmm now i see that you said it wasnt rectified.. my bad i scanned right by it...

When i was very young Dad did that experiment with DC.
As i recall his oxygen side copper wire made no bubbles, so Dad changed it to graphite from a dry cell. That fixed it.

Perhaps the oxygen side copper goes into solution or makes copper oxide ?

That'd leave hydrogen at both electrodes for AC just on opposite half cycles.

Plausible ?

fits N O's recollections and mine too.

 

[sophiecentaur]

Back to the plot.
Most fish (and presumable sea monsters too) are pretty sensitive to electric fields. Sharks detect the neural currents in fish and recognise injured ones this way, I believe. You certainly wouldn't need a vast amount of power for this exercise.

I remember canoeing on the river Wye and passing a water bailiff who was stunning the fish in order to count populations. His equipment was powered by just a car battery and he was there all day.

If you want to set up the most effective field, you would hang one wire from each end of the boat, with a metal (s/s or copper, I guess) plate. A portable generator could supply enough AC power and a transformer could give you, perhaps 50V between the electrodes, which would produce fields of at least 1V/m (fish can detect 1uV/m). I'm not sure whether AC or DC would be better but poetic license would apply here, I'm sure. You could always use a rectifier.

This field between the plates would surround the (fibreglass / wood) hull and should be more than enough to have an effect on your monster. You are not after FRYING the devil, are you - just putting him off? You can actually buy electric shark repellant gear that surfers can carry with them. These use (non-lethal - the swimmer is in there too) just a few volts and are claimed to confuse a nearby shark. The above system would be much more effective.
So the original idea would seem to be a goer!

 

[NascentOxygen]

If I implied that AC was decomposing water I'm sorry. I didn't mean to imply that. I meant to state it unequivocally. Is it difficult to believe that during a half cycle one wire is positive and the other negative so O2 will form on one wire and twice as much H2 forms on the other? During the next half cycle the process reverses.

Skeptic 2 meet Skeptic 22!

While it may sound possible that mains AC would alternately liberate O₂ then H₂, I happen to have investigated this very question using a function generator (variable frequency oscillator). As expected, at very low frequency AC (think 0.1 Hz) the electrodes alternately liberate O₂ and H₂. But I found that when the frequency got to just a few Hertz (from memory 4Hz) gas production ceased, though the solution continued to conduct well. Way, way below 50/60 Hz there already was no discernible gas production. When you realize that ions need to be allowed time to migrate to one or other electrode to accept/donate a charge, this becomes understandable.

If you believe that a few mL of an ideal mixture of O2 and H2 won't send a pill bottle bouncing around the room, I urge you to try it.

Ah! With almost any other mixture of homemade gases, yes, it may just be possible, though I do have reservations about miniscule pill bottle volumes. But the H₂-O₂ mixture is a special case, particularly when ignited over water. It makes a satisfying retort, certainly, and that bespeaks high energy. But unlike all other common stoichiometric gas mixtures, the explosion is instantly followed by an implosion. Any inclination for the pill bottle to lift gets countermanded by the suck of water pulling it back down as the vapour of combustion condenses and, volumetrically speaking, vanishes leaving a low-pressure ("vacuum").

Under the circumstances painted, I see your pill bottle filling with water and remaining firmly seated right where it was, unfortunately. There seems no reason for it to do otherwise.

 

[vk6kro]

But the H₂-O₂ mixture is a special case, particularly when ignited over water. It makes a satisfying retort, certainly, and that bespeaks high energy. But unlike all other common stoichiometric gas mixtures, the explosion is instantly followed by an implosion. Any inclination for the pill bottle to lift gets countermanded by the suck of water pulling it back down as the vapour of combustion condenses and, volumetrically speaking, vanishes leaving a low-pressure ("vacuum").

What happens is this:
2 H₂ + O₂ → 2 H₂O (steam)

I have seen the effects of exploding a balloon filled with a stochiometric mixture of Hydrogen and Oxygen.

There was a huge fireball about 2 meters in diameter which burnt the hairs off the arm of the guy holding a lighted taper to the balloon.

There was absolutely no implosion.

 

[NascentOxygen]

I have seen the effects of exploding a balloon filled with a stochiometric mixture of Hydrogen and Oxygen.

So have I, and a most satisfying boom it makes too. But the discussion here is not about a balloon, nor a balloon-sized mixture. It's about a pill-bottle volume, in a pill-bottle wet and sitting over water. Big difference. Most balloon demos use the igniter flame to first burst the balloon then ignite the cloud of uncontained gas. Big difference, though it makes for a good sideshow, with the bang of the H-O combustion augmented by the bang of the rubber balloon bursting.

There was absolutely no implosion.

In air, the implosion quietly follows on the heels of the spectacular explosion. We need a smaller, tougher balloon that doesn't burst for a comparable demonstration. The ignition source must be inside the balloon, and itself cause the balloon no damage.