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I finally figured out how my alchemy system works. The problem is, when my characters perform alchemy, they release loads of hydrogen gas. Why? Well, basically, they will take an object and cause every atom in that object to release one neutron or proton. As the protons leave the atom, they capture an electron, forming a hydrogen atom, and then meet up with other hydrogen atoms to form H2 gas. When Neutrons are released (magically) they decay into a proton and electron which then come together to create a hydrogen atom which then combines with hydrogen to create hydrogen gas. Given this fact, I assume you can guess why my version of alchemy produces lots of hydrogen gas.

The problem is, they live on a planet with an earth-like atmosphere, so that hydrogen gas can cause a massive fire if it just interacts with the oxygen, so my alchemists need to be very careful to not blow things up. Besides this, they may also want to store that hydrogen gas they are producing cause it could be useful, but how do they do that safely... Without blowing things up? Particularly how do they store this volatile material in the pre-modern era, or atleast prevent it from starting fires. There are no other relevant magical abilities I can think of which can be used to control the gas.

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    $\begingroup$ Chemistry nitpick: A bare proton is a hydrogen atom: H+ $\endgroup$ Aug 1, 2023 at 14:22
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    $\begingroup$ Also, something else to consider is that if you kick a proton out of all the nucleii at the same time, you'll quite possibly be generating a large volume of hydrogen gas inside a small space...you may want to consider the rate-of-hydrogen-production against the PV=nRT ideal gas law, and see what kind of pressures and temperatures you might be creating... $\endgroup$
    – Qami
    Aug 1, 2023 at 14:32
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    $\begingroup$ @Qami Pressures and temperatures are critical (pun not intended but useful) to this situation. Off the top of my head H2 gas doesn't automatically burn in open air -- but pressurize the gas in a sufficiently contained volume and add just enough heat, and oh boy it's time to repair the lab again and find a fresh "oLS $\endgroup$ Aug 1, 2023 at 14:41
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    $\begingroup$ @CodeswithHammer Exactly! And the fun part is that this could potentially even be happening inside a solid object (@skout yes?), in which case there might also be the question of how much pressure it would take to blow the object apart. I feel like alchemy would probably be safer done on a powder that a discrete object. $\endgroup$
    – Qami
    Aug 1, 2023 at 14:59
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    $\begingroup$ The other fun part, from the POV of writing the story, is that this is alchemy not chemistry and scientific approaches aren't used. Alchemists are going to go through a lot of labs (and a lot of lab assistants) before the story gets to the point where the released hydrogen gas reliably doesn't result in a RUD. $\endgroup$ Aug 1, 2023 at 15:31

7 Answers 7

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A balloon

Provided your people do not (yet) use alchemy-generated hydrogen as fuel, so they don't actually need to store the thing, make a balloon, fill it with hydrogen and employ as a zeppelin, or outright release into the heights, the balloon would then explode from inner pressure releasing hydrogen far from inhabited zones. Pros - released hydrogen will not cause fires, as it's lighter than air. Cons - you have to catch the balloon's shell somehow, maybe not a good thing in a medieval society.

Gas burner

If there is a place where alchemy is performed routinely, a gas burner running on hydrogen contained in a glass dome would just do, a free advertisement, water generator, power generator (eventually), a light source and even a stove if needed for mundane use. Pros - you don't store, you burn in a controlled manner, so this "store" is almost infinite. Cons - you might need heat sinks to not overheat the lab should your alchemists overdo material conversion in a short timespan.

As a side effect, your alchemists might also design reverse-alchemy magic process that consumes hydrogen from the surroundings, and creates heavier elements, say copper out of iron in three steps, a large glass dome (a size of a house) could fit for both purposes. And as a detector, a methane/hydrogen balloon could be used, weighted so that it always floats at lower bound of hydrogen within the dome, if it goes too low it's time to burn some gas.

Put it under pressure

Hey, thick iron canisters don't require too modern tech, just add a valve and a pump. Use a low pressure holder like the dome, then start the pump to collect the gas into a smaller canister, then use as required in labs (normal) or plain sell as fuel.

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    $\begingroup$ If you don't have modern tech, you're better off using thick bronze canisters. It's hard to make thick pieces of defect-free iron, and bronze is more forgiving when it ruptures. (Historically, iron cannon barrels were seen as the cheap substitute for proper bronze barrels.) $\endgroup$
    – Mark
    Aug 1, 2023 at 22:07
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    $\begingroup$ Also @mark if your pumps are any good, many steels tends to get brittle in prolonged contact with hydrogen. Cast iron is already brittle compared to modern steels, and I wouldn't like to risk making it worse. $\endgroup$
    – Chris H
    Aug 3, 2023 at 10:48
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This was done in Victorian times. Early chemistry included producing hydrogen gas in bell jars to collect it.

Limelight burners used in theaters were oxygen-hydrogen lamps and they used animal skin or rubberized silk bags to hold both gasses. they leak so they can only store it for a few hours to a few days at most.

gas bags were not new technology, remember hydrogen filled balloon date back to the 1700's

limelight

first hydrogen balloon

EDIT Gasometers were essentially large wooden tanks (built similar to how water tanks are built but double walled), with a water seal at the bottom. these are used to store gas on an industrial scale. Probably too big for your alchemist but a smaller version can easily be built. Smaller ones like the oxygen tank below did not show up until the 1800's but could still be built with earlier technology.

enter image description here

enter image description here

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    $\begingroup$ These were even expanded to the size of buildings as "gasometers" or "gas holders"! $\endgroup$
    – IronEagle
    Aug 3, 2023 at 3:04
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    $\begingroup$ @IronEagle Great catch I will add some stuff about gasometers. $\endgroup$
    – John
    Aug 3, 2023 at 13:02
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Salt Casks

We're already looking to the cask's big brother to store hydrogen today.

Salt caverns are artificial cavities which are created in geological salt deposits. Future caverns are generally located at a depth of 500 to 1,500 metres. They are three times higher than the Arc de Triomphe. To create such a cavern, it is first necessary to drill into the salt. The second stage consists in injecting water into the salt to dissolve it. The resulting brine (water mixed with salt) is extracted and leaves room for a large, tight cavern where hydrogen can be stored under pressure. (Source)

It all started when humanity needed a place to store vast amounts of excess natural gas.

The first use of a solution-mined salt cavern for storing natural gas was in 1961 when Southeastern Michigan Gas Co. leased, from the Morton Salt Co., and converted an abandoned salt cavern formed by routine brine production. ...

The first such cavern created specifically for the storage of natural gas was constructed by the Saskatchewan Power Corp. and became operational in 1961 The 290,000-bbl cavern, located in Melville, Sask., was constructed in the Prairie Evaporite salt formation at a depth of approximately 3,700 ft.

In the U.S., the first solution-mined salt cavern constructed specifically for the storage of natural gas was completed in the Eminence Salt Dome in Covington County, Miss., in 1970 by Transcontinental Gas Pipe Line Corp. (Source)

But humanity's reason for not doing it until 1961 had nothing to do with the technology needed to form the caverns. Humans have been mining salt underground for 7,000 years.

The history that salt mining in Hallstatt looks back on, is absolutely unique worldwide. During the Neolithic Age – an almost incomprehensible 7,000 years ago – people were already busy here mining for salt. That makes Hallstatt the oldest salt mine in the world! (Source)

In other words, we didn't put two and two together until we had an excess of gas we needed to store. After we figured that out, the leap to hydrogen was logical. But your people have a reason to deal with the need to store gas at a much earlier time! Luckily, the tech for creating the cavern is literally neolithic.

The problem is the tech sealing the entrance.

But I think there's a logical jump to be made here, too, because your earliest alchemists — not knowing yet what the consequences of their efforts could be — lost a few limbs before realizing they needed to contain the effluvia of their efforts (and they were tired if sounding like chipmunks, anyway). But like all good innovators, they weren't trying to move mountains first. They were trying to do small things requiring small capture.

Thus was born the salt cask. A bottle or box a quarter to a half cubic meter in size for which someone discovered that a concoction of (oh, yeah!) tree sap, frog guts, shredded hemp, and a pinch of fine silica could seal in place the openings with small metal disks and simple valves.

Once you have it working for a cask, the move to a cave is just a matter of logistics! Well... and bricks. Lots of bricks.

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  • $\begingroup$ Let's say they did their alchemy in water, not cause it's necessary, but to help for protection, and then they turned this water into brine, covered it with a metal lid and then sealed this metal lid with materials. Would this alchemy pot be able to store the hydrogen gas by this means? $\endgroup$
    – skout
    Aug 1, 2023 at 14:19
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    $\begingroup$ @skout that all seems very unnecessary. Just use the pot. No need for water or brine or a metal lid. Unless you're trying to make some sort of battery or chlorine bomb. $\endgroup$
    – OrangeDog
    Aug 1, 2023 at 14:54
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    $\begingroup$ @skout You've explained nothing about the pot. It's not the presence of salt that makes this work - it's the density of salt as a solid. The moment you dissolve salt into anything you've ruined that ability. Hydrogen, being as light as it is, will percolate through almost any fluid and not be contained. That means the issue isn't the brine (no usefulness there), the issue is still the pot - thus my suggestion of salt casks. $\endgroup$
    – JBH
    Aug 1, 2023 at 14:59
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    $\begingroup$ @JBH if there's any pressure (needed to store a decent quantity) you also need to withstand that. I doubt the tensile strength of NaCl is that great, especially as you'd struggle to get a single crystal. Underground you've got rock under compressive strain; the salt is just the sealant. So your salt would have to be formed in something pretty strong and stiff to avoid cracking the salt liner- I assume you mean the cask isn't entirely salt, of course. $\endgroup$
    – Chris H
    Aug 3, 2023 at 10:57
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    $\begingroup$ @ChrisH That's a good point. Now we're lining a strong container with solid salt. However, I don't believe we're trying to achieve modern pressures (if the alchemists want to move a mountain they'll need to live with the consequences - magic systems need weaknesses), but I can see both wood and, for the wealthy, metal containment systems. I can also see developing a reasonably early-tech controlled release system. What's the sign of an alchemist? A chimney with an eternal flame atop it. $\endgroup$
    – JBH
    Aug 3, 2023 at 12:58
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Particularly how do they store this volatile material in the pre-modern era,

  1. In metal.
    This can be extremely thin.
    Beaten gold leaf shells over a support of your choice may work.

Any other cheaper and available metal will work.
Hydrogen diffuses into metals, embrittling them.
Probably not a major problem in the short term.

  1. Glass. Of a number of sorts.
    Again, thickness not a major issue.
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Store the hydrogen as water (by "burning" it in the presence of oxygen), and release it as-needed via electrolysis. You'll want to control the rates at which oxygen & hydrogen interact with some narrow glass tubing, possibly joining the oxygen & hydrogen lines (or normal-air & hydrogen lines) at a flame to kick-start the reaction. (Think "pilot light on a gas furnace".) As long as you don't have large build-ups of hydrogen, you needn't worry about explosions.

Hydrogen readily diffuses through solid materials, but storage via chemistry avoids that, and electrolysis has been possible since the late 18th century, with chemical understanding of it growing over the next few decades.

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Not so much of a problem

Looking at experiments with hydrogen tanks that crack, releasing a huge amount of easily 700bar pressure hydrogen we can see it's pretty safe. Hydrogen is much lighter than air, being the lightest element in existence. This makes it move up into the air and dissipate at a high rate. It is also a nontoxic gas, so you need to do something very wrong to get killed by it.

Your experiments shouldn't release anything close to the amounts of a pressurised tank at once, meaning you have much less risks here. Probably even in not well ventilated area's theres little chance of problems. If you're still uncomfortable, make sure any gas can easily leave your area. High ceilings and proper ventilation will probably do the trick. Though I have to say that Hydrogen gas is so small it is hard to contain. Even in a small area at the amounts you're likely to produce it will move through roofs and walls before any 'dangerous' build up can occur. That is if it doesn't react with oxygen before that to create a nearly insignificant amount of water.

All this is assuming you do not want to use the hydrogen for anything and need to store it.

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    $\begingroup$ I'm not sure I would characterize it as "pretty safe" given how easy it is to find incidents like this: powermag.com/lessons-learned-from-a-hydrogen-explosion Yes, there are ways to design systems and buildings to minimize the risk of an explosion, but that's not the same thing as implying you don't need to take any safety precautions. $\endgroup$ Aug 3, 2023 at 19:46
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    $\begingroup$ @SarahMesser I did oversell the safety of the tank. Regardless, the contents of your article support my answer. From 'Understanding Hydrogen' to 'Toxicity/Poison' shows it needs very specific conditions to pose any danger. A rupturing tank of hydrogen is a worst case scenario, while the amount of hydrogen in the question will be much, much less over way longer time scales. It shouldn't come close to meeting any of the dangerous situations. If it does ignite or similar, I expect it to be few enough hydrogen not to pose any significant danger. $\endgroup$
    – Trioxidane
    Aug 4, 2023 at 8:06
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The hydrogen and oxygen that are reacting here will produce water vapours. Although that wouldn't be dangerous enough, but the vapours may be hindering your alchemical work. If you were to keep the container open, the hydrogen will react with the excess oxygen outside.

So keep the container tightly closed and whatever oxygen is present inside, will react with hydrogen to produce water vapors. You can easily rid these vapours by placing a good chunk of water adsorbing substance like calcium chloride. As more and more water is adsorbed, more hydrogen and oxygen will react according to Le Chatelier's principle and finally when you open the lid, there will be no leftover hydrogen that may explosively react with atmosphere.

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    $\begingroup$ 1: it's the reaction itself that's hazardous, not the water produced. 2: what oxygen? It's a closed container, any trapped oxygen will be consumed. 3: Le Chatelier's principle really isn't relevant here. It takes temperatures of thousands of degrees Celsius to decompose significant amounts of water...otherwise, every container of water would form an oxygen/hydrogen atmosphere, as would Earth itself, and such mixtures wouldn't be explosive. $\endgroup$ Aug 3, 2023 at 13:26

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