6
$\begingroup$

It’s been awhile since I’ve been on here, and in all that time, I’ve developed my fictional world by a lot. But I’m still confused by something. You see, the society of my world is one modeled on Europe during the Middle Ages, yet they possess firearms. Unlike normal guns, these don’t use gunpowder or bullets, rather, they use liquid nitrogen. My question is, could there be a way for a primitive society to develop weapons like this?

$\endgroup$
14
  • 5
    $\begingroup$ Is it stated in your fiction where they get liquid nitrogen from? Or is that the question: how to produce liquid nitrogen with medieval tech? $\endgroup$
    – Willk
    May 12, 2020 at 17:09
  • 2
    $\begingroup$ Almost anything "could" be possible. However, it beggars belief, so you better be a very good storyteller to handwave how this barbaric kingdom can liquefy air but doesn't understand how to prevent the bubonic plague nor apply any of the ancilliary energy and industrial technologies...which it somehow obtained and uses without any schools...to improve the impoverished quality of life. $\endgroup$
    – user535733
    May 12, 2020 at 17:13
  • 4
    $\begingroup$ Worth noting also that while liquefying air is by far the largest obstacle, storing the stuff in a battlefield-usable container would require metallurgy that they also wouldn't have available, and projecting it under pressure would require materials science that they wouldn't have available. So whole disciplines of study would need to be present, which would make conventional firearms far more reasonable. $\endgroup$
    – jdunlop
    May 12, 2020 at 17:17
  • 4
    $\begingroup$ Even our modern technological society can't produce any practical firearms which use liquid nitrogen as propellant, so... $\endgroup$
    – vsz
    May 13, 2020 at 5:17
  • 2
    $\begingroup$ "these don’t use gunpowder or bullets, rather, they use [an element that rapidly expands upon release]" : Girandoni air rifle "made from hammered sheet iron held together with rivets and sealed by brazing, proved very difficult to manufacture using the techniques of the period and were always in short supply." - both braising and rivets are c. 3000 BC. The degree to which you handwave "very difficult to manufacture" is your prerogative. $\endgroup$
    – Mazura
    May 13, 2020 at 7:23

6 Answers 6

19
$\begingroup$

could there be a way for a primitive society to develop weapons like this?

No.

  • liquefying air is well beyond medieval tech level.

    The most common process for the preparation of liquid air is the two-column Hampson–Linde cycle using the Joule–Thomson effect. Air is fed at high pressure (>60 psig, or 520 kPa) into the lower column, in which it is separated into pure nitrogen and oxygen-rich liquid. The rich liquid and some of the nitrogen are fed as reflux into the upper column, which operates at low pressure (<10 psig, or 170 kPa), where the final separation into pure nitrogen and oxygen occurs. A raw argon product can be removed from the middle of the upper column for further purification.

    Air can also be liquefied by Claude's process, which combines cooling by Joule–Thomson effect, isentropic expansion and regenerative cooling.

  • handling liquid nitrogen is also well beyond medieval technology, and rather unpractical even in modern times. Surely not something you want on a battlefield.

$\endgroup$
1
  • 2
    $\begingroup$ Pretty sure it would be possible to liquefy air with much more primitive means than what the modern industrial processes use, if you don't mind bad energy efficiency. ...not with medieval means though, that's true. $\endgroup$ May 13, 2020 at 18:41
8
$\begingroup$

Aside from being cool (pun intended) what would be the use of a liquid nitrogen weapon? It's really not that dangerous!

Liquid nitrogen is cold; but it has a pretty low heat capacity so unless you pour a bucket directly on someone it's not going to do a lot, and the gas itself is entirely harmless. A common disposal method is just to pour it on the ground outside, and you don't even have to take too much care while doing so. You'd do far more damage with conventional chemicals like hot oil or acids.

The most dangerous thing you can do with liquid nitrogen is have it in an enclosed space and let it displace all the oxygen; an intriguing and subtle way to assassinate a pesky king, but not really a weapon in the conventional sense.

$\endgroup$
1
  • $\begingroup$ You missed the obvious one - rapid expansion of liquid to gas... just like firearms do, but solid to gas in that case. You can certainly create "bombs" with it in an enclosed tube. I imagine you could use it to propel a bullet too. $\endgroup$
    – bob1
    May 13, 2020 at 23:14
6
$\begingroup$

could there be a way for a primitive society to develop weapons like this?

Yes...

...in a slightly kinky, low fantasy world, one can imagine how such "firearms" work. For example:

your armoury could make use of cryogrobbins, a kind of wee imp that destills nitrogen from the air as a byproduct of its own respiration. This is for the cryogrobbin a waste product that it periodically pisses through relatively normal methods.

Your gunsmiths will take advantage of this faculty by fixing one cryogrobbin to a kind of cartridge in such a way that the poor wee fellow is bunged up. This builds up pressure in the bladder over time. When it comes time to load the gunne, the musqueteer will simply grab a pre-bunged crygrobbin cartridge from his pouch and shove the poor fellow into the breach of the gunne and pack the ball in from the muzzle. When it comes time to fire the gunne, the musqueteer pulls the trigger which releases the bung and applies pressure to the cryogrobbin's abdomen, forcing a rapid & explosive discharge of liquid nitrogen.

The rapid discharge and expansion propels the projectile in the expected manner.

Magic. Pure magic.

$\endgroup$
4
  • 5
    $\begingroup$ Yes pure magic. Why not do away with the goblin thing and just magic the liquid nitrogen into existence when you need it. That would also solve the storage problem. $\endgroup$
    – Slarty
    May 12, 2020 at 20:05
  • $\begingroup$ Indeed! Magic applied to technology. This is a "low fantasy" setting after all. If you ignore the inherent magic, you can't really offer a viable solution. $\endgroup$
    – elemtilas
    May 12, 2020 at 20:26
  • $\begingroup$ Or there could have been some journey long ago to a cold region of the Earth where the explorers stumbled across...etc. Perhaps it's not exactly "liquid nitrogen" but it certainly does what you need it to do. $\endgroup$ May 13, 2020 at 15:41
  • 1
    $\begingroup$ This is probably the funniest answer. +1 $\endgroup$
    – pg4919
    May 13, 2020 at 22:48
2
$\begingroup$

It would not be possible to create liquid nitrogen using medieval technology.

However for the purposes of a story, it might be possible to suspend disbelief in some people (who were not familiar with any cryogenic technology), although even then it would still be very difficult.

How about a large ship with the hull sealed with lead sheeting and capsized in deep water by adding some huge rocks to the mast. Then take a tube to the surface and let the highly compressed air caught in the hull out. If enough air rushes out and expands rapidly at the surface and the process continues for long enough the temperature should drop.

You’re not really going to get liquid nitrogen by this method, but you might be able to fool some people this way.

Alternatively since your not using the science based tab just use magic.

$\endgroup$
1
  • $\begingroup$ OP has already placed the [low fantasy] tag: "worlds where magic exists, but is rare". $\endgroup$
    – elemtilas
    May 12, 2020 at 20:30
0
$\begingroup$

It won't work for mediaeval humans in a terrestrial setting. There are only two ways to change the phase of the gas, cooling and compression. The tech of the day can't provide adequate seals or refrigeration.

Aliens on a gas giant is another story. They could do with with a winch, a long rope and an insulated bottle.

$\endgroup$
0
$\begingroup$

As others have noted, liquid nitrogen isn't really possible or practical.

One liquid that is available that could be more dangerous than liquid nitrogen is alcohol, which can be cooled down to temperatures well below the coldest places on earth. It also has a much higher boiling point, and tends to stick to things it touches, including skin.

If you had a means of cooling the liquid down, say, dragging it up a cold mountain, cooling it, and then bringing it back down quickly (maybe via a slide or something), you could possibly load it into device that sprays it, causing frostbite.

Distilling would be cumbersome, though, and this could be a resource-intensive process.

Additionally, propelling the liquid would be difficult, especially in a manner that would allow it to remain insulated for months at a time, which one might need on a military campaign. It would be extremely heavy to carry around in a large container that would be able to insulate it.

Also, it would be nearly impossible to use over a long range. Air resistance and turbulence would increase the temperature and slow down the launched liquid, limiting both its range and effectiveness.

For defensive purposes, such as pouring a large container of it over a wall, it might be more practical, but hot tar/oil also does the trick, but requires less preparation/maintenance.

Perhaps you could find some sort of highly endothermic reaction involving two chemicals commonly available (perhaps produced by some creature, as others have suggested), and they violently react in in a way that draws in heat from their surroundings (e.g., air, skin, water, themselves.). A projectile could simply include both chemicals separated in a pouch that tears upon hitting a target. It could also have secondary poisonous effects that would eventually kill/maim the target.

$\endgroup$

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .