So, dragons are hexapodal creatures, slightly larger than most draft horses (around 190-200 cm at the withers). Compared to the Quetzalcoatlus, dragons have twice the muscles mass in the pectoral region, but the length of the fibers stays consistent. Basically, the chest is just as deep, but the length is extended.

The extra muscle is attached to the heavily modified humerus. Dragon bones are very strong, due to their microscopic structure, which mimics limpet teeth.

That's how dragons remain volant, despite their size. Now, their breath weapon is a two-component acid, aqua regia. Its constituents, nitric acid and hydrochloric acid, are stored separately for safety reasons and only combine moments before exiting the dragon's mouth. Still, having too much acid could interfere with the dragon's ability to fly.

On top of that, the dragon's saliva and mucus are only able to stall (but not completely stop) and (with sodium bicarbonate) neutralize the acids, when present in large-enough quantities.

The breath weapon is useful for dealing with humans and their equipment, but not for much else.

Dragons usually spray targets with the acids, so the two components don't really have a chance to stay combined.

Given that, what's the realistic amount of aqua regia (so, the sum of the two components in liters) a dragon should store?

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    $\begingroup$ Just a note: aqua regia is neither more nor less reactive with organic materials than the component acids. It's more reactive with gold, but that's of little concern for the dragon. $\endgroup$ – AlexP Feb 5 at 20:11
  • $\begingroup$ @AlexP Aqua regia is only a temporary state of the mixture of these two acids, so combining them long before it's necessary defeats the purpose of aqua regia. $\endgroup$ – Mephistopheles Feb 5 at 20:16
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    $\begingroup$ My comment is that there is no "purpose of aqua regia". Aqua regia is not more reactive with knights etc. than the nitric acid on its own. Unless the knight is made of gold, of course. $\endgroup$ – AlexP Feb 5 at 20:18
  • $\begingroup$ @AlexP Not really, but the dragon does "drool" on objects if he wants to dissolve them and aqua regia simply just expands the list of dissolvable thing. $\endgroup$ – Mephistopheles Feb 5 at 20:24
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    $\begingroup$ Dragons or lore are gold hoarders. I see a story here since the OP is obviously putting a lot of effort into a story based around aqua regia in dragons. I remember you said they are as smart as humans, but immature... maybe you have a story here about a dragon that turned a whole town's fortune into aqueous gold because presumably that's what aqua regia dragons do. Then, the story is about the discovery about where the gold went, and negotiations on how to get it back.... or something. Anyways, acid is a bad weapon compared to, for example, the horns on a bull, etc. $\endgroup$ – doe Feb 6 at 2:50

Did the dragons evolve, or were they birthed with magic? If birthed with magic, then it might as well just be matched to the average amount of humans they run into in a day.

If they evolved, then actually how much acid breath they have has nothing to do with humans, because dragons evolved before them (or at least before humans had weapons).

So if not evolved for humans, what was the original purpose of the acid? This is important because sometimes evolution works so hard on one thing that it is an impediment to other things. Just try and imagine a male peacock trying to escape a predator.

If the original use of the acid was something massively essential for survival and selection, they might carry so much that it actually hurts their flying distance and limits their lifespan by slowly dissolving their teeth (an animal that can't chew starves). A fun opportunity to consider their past situation and enemies.

But if they used it for something less, like maybe occasionally burning holes in rocks to hide eggs, a liter is more than enough (one human a day worth).

Although as AlexP points out, this particular acid is worst case scenario for a dragon, since its claim to fame is it dissolves gold. That's more of a curse you would put on a poor hoarding dragon who just wants to lick his treasure!

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  • $\begingroup$ Just because it's useful against humans doesn't mean it was meant for them specifically, they just happen to be a threat. It's simply a defense mechanism, and therefore, the more the dragon can use it the best. Think of how skunks are essentially defenseless for about a week after a full spray. Additionally, an animal can have more than one defense mechanism, as seen in the frilled lizard's many strategies to escape predators, with flight here clearly being the focus over the acid, like he said himself. $\endgroup$ – ProjectApex May 18 at 15:10

My acid spitting dragons use sulphuric acid, not hydrocloric acid.

The chemistry is pretty simple. When an acid is put in water, it disassociates into H+ ions. Hydrocloric acid is already in water and mostly disassociated with a ratio of 30-40% acid and the rest water. Sulphuric acid on the other hand is 98% acid and 2% water, so it is seeking water to disassociate with.

When my dragon breathes his acid breath on the human trying to kill him, it immediately dehydrates the skin it comes in contact with, the skin carbonizes resulting in 3rd degree burns.

Your aqua-regia dragon is more into processing and refining gold than dealing with humans or other beasts that might attack it. The Hydrocloric acid will burn eventually, but the affected areas don't immediately react to the acid.

In both cases, the dragon's mouth and surfaces that may have been affected by the acid would be doused in glands that create a base mucous coating that stops any major damage from the remaining acid. This mixture causes "drooling" and is a way of disposing the mixture off of the dragon.

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