Electrolysis was a popular idea for how mermaids would generate oxygen for their guests. This leads to another question: Is it possible to perform electrolysis with pre-modern technology?

Electrolysis was apparently first performed in the 19th century, though not as an intentional electrolysis experiment. From what I understood of the process, it seemed possible, as there are some electrical experiments back in history, and it appeared that electrolysis only requires power, a solution, and two electrodes?

But is this actually the case? Could medieval people, or a fictional people with medieval or earlier technology, have performed electrolysis, and collected and separated samples from this process (specifically oxygen and hydrogen)?

Additionally, if it's not too much to ask, I would ask when in history this first could have become possible.

  • $\begingroup$ Hydrogen was discovered in the 18th century and is very hard to store. So absolutely not randomly just for the fun of doing it. Our understanding of chemistry was not nearly there yet. What do you want to accomplish? If there is need to do something, people will find a solution. Much canbe done, but it wouldn't be done systematically without any economic thought behind it. Right now, your question is very specific and random. Could you describe what you want to do in greater detail? $\endgroup$
    – Raditz_35
    Dec 26, 2020 at 20:44
  • $\begingroup$ It was possible at any point you'd like in written history. To make a battery you need three things: copper (predates written history), zinc (middle of the 3rd millennium BCE), and an electrolyte, such as a dilute acid solution (vinegar or lemon juice work fine) or even just brine. Beware that electrolysis using primary cells (= non-rechargeable batteries) is an extremely expensive way of making oxygen. You'd need to be filthy rich to afford a year's supply of oxygen made this way. $\endgroup$
    – AlexP
    Dec 26, 2020 at 20:47
  • $\begingroup$ You can rub cat's fur to generate static electricity. Appropriate construction of kitty corrals and discharge stations you could the harvest the needed power. Static electricity has been known since 600 BC $\endgroup$ Dec 26, 2020 at 20:56
  • $\begingroup$ @Raditz_35 What is random about it? I am asking how possible electrolysis is/was in the past. I'm not sure what you mean about economics, in relation to the question. If it is possible, and only needs economic incentive to be achieved, that can be stated. My curiosity is how plausible it is for a pre-modern society to develop electrolysis, as I heard it suggested it was not possible. $\endgroup$
    – Johnny
    Dec 26, 2020 at 20:57
  • $\begingroup$ @AlexP That's the impression I got, though I was challenged on the idea electrolysis was possible in pre-modern times (they mentioned something about platinum, but didn't explain). With the mermaids in the other question, I figured they might be able to power it with a saltwater breed of electric eel. $\endgroup$
    – Johnny
    Dec 26, 2020 at 21:00

2 Answers 2


The route to pre-industrial electrolysis

One plausible technological route to electrolysis is electroplating. It is documented that the Moche culture was able to perform such feats. Since the Moche culture ended somewhen around 700 AD, it should count as pre-modern.

People might notice that when electroplating large objects (or with higher voltage than usual) that torches burn brighter when entering a badly ventilated electroplater or observe and decide to study gas bubbles forming.

It would be quiet plausible that these bubbles which make torches burn brighter become an religious obsession. Prompting a land based culture to actively invest it. However such a pre-modern culture will be restricted to generating electricity from biochemistry from agricultural goods or maybe static electricity from friction.

As pcman noticed this technology should be "unlockable" to bronze age with a lot of agricultural output.

Electrolysis wouldn't be the way to go for submarine societies because there is perfectly fine air on top of the ocean.

As for underwater mermaid based cultures harnessing animal electricity this would be a really inefficient way to generate oxygen. An group of electric eal one of which is spasm at any point in time (probably >100) might generate 30W generously. Assuming there is non conversion loss it would take 100 of such eal groups to produce barly enough oxygen to

Swimming back with canisters of atmosphere (breathing pure oxygen for humans under see pressure is really bad) is less energy intensive and could be mostly automated if rotary energy, long chains and springs are available. It would basically be Diving bell on a raft (so air can be exchanged) which can be pulled down via chains. This would still be luxury as a human guest would require >4 car interiors worth of air to be moved per day.

Algae are no possibility even if the farms are very close to the ocean surface. The algea would need to be kept in (room sized, transparent, air tight) glass green houses close to the ocean surface with some gas pumping system. This requires modern technologies.

  • $\begingroup$ The bulk of your answer seems to be concerned with the mermaid/oxygen context rather than developing electrolysis. I recommend deleting everything after the first paragraph and expanding the electroplating→electrolysis connection. $\endgroup$
    – rek
    Jan 3, 2021 at 17:56
  • $\begingroup$ Welcome, Worldsmith! Thank you for sharing the great source with me, it's incredible to have a source that speaks about electroplating prior to the Viking Age. You present a reasonable idea for how they work it out, too. From my calculations, it would take ~5kWh of energy per person, and current species of electric eel might be able to produce 215W for one hour. If over a day they managed a quarter of this on average, you could get enough oxygen from four electric eels, if a tenth then 10 fish. It's true that you might have an easier time with a crane. $\endgroup$
    – Johnny
    Jan 3, 2021 at 18:00
  • $\begingroup$ @rek That seems unnecessary. He went to the trouble of looking up the asker's apparent prime concern, and so added extra-credit to the answer. I would just put it under a separate header. $\endgroup$
    – Johnny
    Jan 3, 2021 at 18:01
  • $\begingroup$ @Johnny thank you, Are the headings fine as they are? I find your electric eal numbers to high. A better way to estimate the impact on society would be to look how much fish would be required to feed the eal blackbox. Which would be 2.5 kg of salmon meat per hour, ignoring energy losses. So 200+ kg of high in the food chain fish per day per human guest sounds about right. $\endgroup$ Jan 3, 2021 at 18:34
  • 1
    $\begingroup$ @worldsmithhelper NP, I appreciated your answer. Headings seem fine. The numbers are optimal conditions, and are based off the data I and another guy could find, from various papers. I could've assumed a lot more. That would be 100kg of salmon, but calories are highly flawed and have been increasingly in question. Electric eels have been recorded to produce up to 860W, and there are reports of them maintaining high voltage for extended periods, "more than an hour," one source claimed. Yet, it's unlikely they would develop bioelectricity if it took more calories than it gained. $\endgroup$
    – Johnny
    Jan 3, 2021 at 19:05

Yes. If they learned how to do it.

Functionally, they had all the tools needed. Except for the knowledge of how to do it.

Electrolysis is easy, all you need is an voltage source (a battery works fine), some conductors, and the electrodes.

Of course, this presupposes that you have the concept of electricity. And know how to build a battery. And the concept that materials can be composed out of other materials, and that the correct process can be used to split and recombine them.

In effect, you need to somehow learn the basic concepts of chemistry and electricity and the nature of the states of matter (solid, liquid, gas). Not much depth of knowledge in any of these fields, but the fundamental concepts are needed. In Earth history, those knowledge and concepts only got together towards 1800, when Alessandro Volta build his first working batteries, and developed electrolysis at the same time. Although it was several years before he really understood why it worked, his initial theories were a bit off.

So, that's quite a lot of knowledge required. But in terms of tools, infrastructure and materials? No problem at all. The needed materials were available in old Egypt already. As soon as a culture could make vinegar, smelt iron, and make copper wires.(zinc helps, a lot, but is optional)

Frankly, its amazing that none of the experimenting alchemists through history have stumbled across the concept of batteries, and once you have batteries then electrolysis follows naturally, and that provides an excellent insight into the nature of gases, and eventually true chemistry. Possibly because most natural battery cells have a very weak voltage from one cell (typically under 1.8v), and need the cells connected in series to make enough voltage for a visible spark?

  • $\begingroup$ Thanks. This was my understanding of the subject, but I had it violently questioned enough that I wanted a second opinion. My general idea was that mermaids would develop this technology via experimenting with bioelectrical animals. They want to understand how they shock things through water, for their safety and utility, and this eventually leads to experiments where you electrigy water via electrodes. Only takes a nearby fire, and the "pop" of hydrogen for them to notice something weird is going on, and they could invent electrolysis. $\endgroup$
    – Johnny
    Dec 26, 2020 at 21:10

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