# Cryogenic grenades in medieval time

In the 12th century China invented primitive rocket launchers, repeating ballistas, guns and cannons and a lot of other crazy gun powder based weapons.

So I wonder could the same level of technology be used to create cryogenic grenades?

I think the easier and the most effective way would be using liquid nitrogen as it can easily cause frost bites and potentially kill.

I guess some dry ice and alcohol is enough to make big quantities of liquid nitrogen, but where are they going to get frozen carbon dioxide?

Or are there other similar elements and compounds that can be obtained more easily?

• I don't think China had the technology to make dry ice. – Bellerophon Aug 26 '16 at 12:45
• How do you make liquid nitrogen using dry ice? – JDługosz Aug 26 '16 at 12:52
• @Asoub Sorry to disappoint but I don't think cryogenic grenades exist. – Bellerophon Aug 26 '16 at 12:58
• If we don't have cryogenic grenades then you can bet that people 500 - 700 years ago didn't either. Sorry, it's just an incredibly silly questions. – AndreiROM Aug 26 '16 at 12:59
• @渡し守シャロン It's called "poor man's LN" but it's not actual liquid nitrogen. It's a liquid at the same temperature as the dry ice. – John Feltz Aug 26 '16 at 13:57

# No

You are talking about trying to make refrigeration before people even have a concept of things such as "phases of matter", that is to say Gas/Liquid/Solid, or even heat as defined in the laws of thermodynamics. These are necessary things if you intend to invent refrigeration.

....which is to say your question is as if you asked whether a child could do a 2 meter high-jump before they have learned to walk

...or if they could make M&M's before they knew about peanuts and chocolate.

Answer is: no, they could not.

Daniel Gabriel Fahrenheit defined his temperature scale in 1724 with 0 F at a temperature that later turned out to be 255.4 Kelvin, or minus 17.8°C. This temperature was chosen because it was the coldest that was achievable through artificial means and that was stable.

You are asking if they more than 500 years earlier — and before the scientific revolution — could have achieved a temperature that was about 100 degrees Kelvin colder than what was achievable in the 18th century. No, they could not. Not with any kind of realism involved.

Also to point out: rubbing alcohol and dry ice does not at all reach the temperatures of "liquid nitrogen". I will assume you meant "cryogenic fluid". But you still need refrigeration to make dry ice.

Finally, as others have said: cryogenic grenades are pretty much pointless compared to making exploding / burning grenades, and much harder to achieve.

• I make the case (in my answer) that these things are not necessary to notice some physical effect that causes refrideration. Once noticed it could be Heron-punked into working refrigeration – JDługosz Aug 27 '16 at 4:14

Two problems:

1. Cryogenic fluids aren't actually that dangerous. Dipping your hand in them is a really bad idea, but getting splashed with them is a different matter. Gunpowder grenades would be better weapons.

2. Liquid gasses weren't achieved until the nineteenth century, and are a prerequisite for making dry ice. There's no way to make them with early gunpowder-era technology.

• Even dipping your hand in them may not be that bad of an idea, as it creates a layer of gaseous nitrogen around your hand for a while. Not helpful as a weapon either way. – Volker Siegel Aug 26 '16 at 15:18
• Gunpowder grenades aren't even that lethal without shrapnel. Most "grenades" are fragmentation grenades. That said, if you're really bored in a lab, you can make tiny fragmentation grenades with 1.5 mL eppendorf tubes and liquid nitrogen. The tubes are made extremely brittle by the cold, and if you fill them with a little, as it boils the pressure quickly ruptures the plastic into shards. This is all theoretical, I have never done such a thing. – Nick T Aug 26 '16 at 20:41
• Dipping your finger in LN2 is usually okay (but dont do it) until your finger gets cold enough that the LN2 is no longer boiling rapidly and then you would tend to lose the finger soon thereafter. My (sadistic) chem engineering prof suggested holding contests to see who could hold their finger in the longest. – Spehro Pefhany Aug 27 '16 at 8:44
• Make sure the teacher wins. – JDługosz Aug 27 '16 at 10:49
• @SpehroPefhany Did he suggest the same for liquid lead? – Draco18s Jun 21 '17 at 19:21

…but where are they going to get frozen carbon dioxide? Or are there other similar elements and compounds that can be obtained more easily? … could the same level of technology be used to create cryogenic grenades?

I don’t think a cryogenic grenade is very useful, but it is possible to build a hand-cranked refrigerator. This video shows a refrigerator that works by stretching rubber bands (!), and illustrates that many processes are available that cool when they do mechanical work. Anything of the sort can be used to build a heat pump.

So, yes, the inventor could produce a cooling effect without relying on whole industries that did not exist, and it might occur in a form that is something he would notice (in the video, he points out that the rubber feels noticibly cold against his lips) and not just something he wouldn’t experience without a lot of apparatus that doesn’t have any other purpose. That is, someone could discover it from just playing around.

Once cooling can be done at all and he gets the idea to amp it up, it’s just a matter of scaling up the process and then repeating multiple stages to get colder and colder. CO₂ condensation will be noticed as the experiments progress. This will be plausible enough for most readers — even in “hard” SF the real technical difficulties are trivialized.

• You still haven't explained how one can go from "slightly cool against my lips" to "freezes enemy soldiers". There's many orders of magnitude difference (and difficulty) between the two, and that needs to be bridged before this question is answered. – Azuaron Aug 26 '16 at 13:29
• @Azuaron The answer doesn't suggest cryogenic grenades can freeze enemy soldiers. In fact, JDlugosz says "I don’t think a cryogenic grenade is very useful", so there's no suggestion of freezing soldiers. He indicates the possibility of cooling techniques getting close to frozen CO2, but doesn't mention achieving liquid nitrogen. This is more about how possible it is to make cryogenic liquids, but not make cryogenic grenades. – a4android Aug 27 '16 at 2:26
• @a4android That is the problem in a nutshell, yes, given that the question is about cryogenic grenades. – Azuaron Aug 27 '16 at 10:21
• The question is multi-part and more than just the title line. See the actual question in the body of the OP, that I quoted. – JDługosz Aug 27 '16 at 10:47
• "it’s just a matter of scaling up the process and then repeating multiple stages" - and living forever is just a matter of not dying. Seriously considered downvoting based on this statement. Complete lack of awareness of the technical difficulties involved in practical cryonics. – WhatRoughBeast Jun 21 '17 at 14:06

Assuming (big assumption) that someone there discovered the relationship between pressure and temperature, they would have had the manufacturing technology to make a cryogenic refrigeration unit. (They're really not that complicated. Would be expensive, but a competent blacksmith could do it.)

Of course, then you have to power the thing. No way you could do it feasibly to make any significant quantity with just muscle power. But if they've worked out the relationship between pressure and temperature well enough to build the cooling unit, you just run it in reverse and you have a stirling engine.

Of course, now that you have stirling engines, you're rapidly leaving the mediaeval technology level behind...

And then there's the fact that cryogenic weapons just won't be that effective compared to thermobaric weapons. The maximum temperature differential you can cause by cooling is probably about 200C. You can easily cause 1500C worth of temperature differential by heating, probably more. The higher the temperature differential, the faster the weapon will be effective.

So, yeah, you can suffocate people with liquid nitrogen, but you need either an enclosed space, or really quite a lot of it. Freezing things requires extended contact with it, and a simple raincoat will provide a great deal of protection. A grenade worth probably wouldn't be that useful. You can find videos of physics instructors playing with that much with no side effects.

Much more likely would be to use the liquid oxygen acquired by liquefying air as an oxidizer for charcoal. It's a lot more potent than saltpetre, and gets you an explosive more powerful than TNT. If you want, you can use the liquid nitrogen to convert more of the heat into pressure as well. Depends on if your goal is to light things on fire or crush them.

One of the biggest dangers in dealing with cryogenic materials is asphyxiation. Nitrogen is heavier than air and tends to displace oxygen. You can be dead fairly promptly if there is a big leak. See any of the University health and safety procedures for details. We have oxygen monitors wherever there is a large dewar.

A possible use for an LN2 grenade (more likely a bomb) would be to kill people in a cave or underground warren of some kind (or maybe inside vast greenhouses). The liquid form would be compact and thus easier to transport than compressed gas. Its not poisonous so it would not leave any lasting poisons and probably plants would survive (assuming they could survive in the first place). Under the right (perhaps somewhat contrived) circumstances it could be comparable with a modern neutron bomb that kills people (and higher animals) but leaves infrastructure intact.

The Chinese had fairly precise mechanisms such as clocks and abundant labor, chemical and animal power so they could probably have produced LN2 if it was valuable to them. Consider other ancient devices such as the Antikythera mechanism from Greece.

• If all you're going for is death by asphyxiation, then making bombs out of dry ice would be much easier and produce the same effect, and would be more efficient besides (dry ice is roughly twice as dense as liquid nitrogen, making it much easier to transport per cubic meter of resulting gas). Though that being said, I'm not sure people of the medieval era could've made dry ice any more than they could've made liquid nitrogen. – Abion47 Nov 29 '18 at 22:17