In The Name of the Wind, Kvothe encounters a chemical (or alchemical substance) called Regim Ignaul Neratum, or "bone-tar". From the safety lecture that accompanies it, we know that it:

  • It's highly caustic ("Spill it on your arm and it'll eat through to the bone in about ten seconds")
  • It boils at room temperature.
  • "The liquid is extremely volatile. As a gas it exhibits surface tension and viscosity, like mercury."
  • "It is heavier than air and does not dissipate."
  • The cloud of gas it evaporates into at room temperature and pressure will spontaneously ignite and burn a "bright sodium-red"

Obviously, this is a fantasy book. If this is an alchemical substance, we can expect it to have behaviors which no-real world chemical has (witness Wil's later demonstration about alchemy breaking "obvious" rules). But that doesn't mean it isn't real.


"The liquid is extremely volatile. As a gas it exhibits surface tension and viscosity, like mercury"

Unfortunately the middle bit is a basically a physical impossibility. Just as gases have no fixed volume, they don't have fixed surfaces either. Thus they can't have surface tension. All gases are miscible with each other, meaning they'll mix in all proportions with other gases. While a very heavy gas like sulfur hexaflouride could temporarily pool at the bottom of a container, and even be poured out and flow along the floor like a liquid, the boundary between the SF6 gas and the air is not sharp and it will eventually evenly mix into the room air by diffusion

The author Patrick Rothfuss studied chemical engineering in university, and might have given it properties that he knew were impossible to make it seem more fantastical or as a little in-joke.

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  • Ooh, that’s a really good catch. I should have noticed that impossibility myself. – Bobson May 24 at 1:42
  • There was an old Fritz Leiber story with a "gas of fixed volume" in it. One of the characters played with it like a bit of silly putty. – Organic Marble May 24 at 12:45

As far as I can tell, there's no real-world substance that has all of those properties, though there are endless kinds of mixtures and compounds you could make to try and approximate them. That might be a better question for a Chemistry site, but I'm not positive they'd consider it on-topic.

The closest I could find, thanks to a post on Arcanum, is a hydrogen/silicon compound called disilane (also called silicon hexahydride).


  • Evaporates at 7 degrees F
  • Combusts spontaneously when exposed to air
  • Is about twice as dense as air.

Unfortunately, I can't find any indication that it's caustic, or what it looks like as a liquid. I'm also skeptical Rothfuss would know about such an obscure chemical, though its possible. Most likely, bone-tar is entirely fictional.

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Another good candidate might be Phosphine.

  • Highliy toxic
  • caustic
  • boils at −125.9 °F
  • highly flamable and pyrophoric (ignites spontaneously)
  • heavier than air.

However, its missing

  • surface tension and viscosity, like mercury.

so no perfect match.

I could well imagine Pat Rothfuss had a specific real-world chemical in mind, he is a self-professed chemistry-geek and originally went to college to study chemical engineering (source).

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  • Good one with that real-world link ;) – Gallifreyan May 15 '17 at 15:58

Chlorine trifluoride

Here is a quote describing it

It is, of course, extremely toxic, but that's the least of the problem. It is hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water—with which it reacts explosively. It can be kept in some of the ordinary structural metals—steel, copper, aluminum, etc.—because of the formation of a thin film of insoluble metal fluoride which protects the bulk of the metal, just as the invisible coat of oxide on aluminum keeps it from burning up in the atmosphere. If, however, this coat is melted or scrubbed off, and has no chance to reform, the operator is confronted with the problem of coping with a metal-fluorine fire. For dealing with this situation, I have always recommended a good pair of running shoes.

I suggest reading into if interested. In short it is toxic, explosive, flammable, highly corrosive, can cause asbestos and ash to burn, when mixed with water it releases by products that eat your bones and nervous system.

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  • 2
    Do you have any evidence to suggest it is in-fact bone-tar? – Edlothiad Oct 15 '17 at 19:21
  • 1
    This is certainly caustic enough, but how does it behave as a gas? Is it a gas at room temperature? Also, if you're going to provide a quote, you should source it. – Bobson Oct 15 '17 at 21:02
  • Note: quote is from Ignition. – DavidW May 24 at 1:44

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