On the Existence of Dragons, Part II

Yet again I have more information on this, and I don't want to turn the original post into one big wall of text. So here's the third post in the "series," enjoy.

Here was my original idea for how a dragon's respiratory system could work:

[Diagram]

Rather than having one pair of lungs exchange carbon dioxide for oxygen in the blood, the dragon has two. Blood first passes through the second pair of lungs, which contain the triethylaluminum or similar, to release the carbon dioxide. Then oxygen is picked up in the first pair of lungs, as usual.

We're assuming that this blood contains a special type of hemoglobin that is unusually effective in picking up oxygen, or that the dragon continues to hold oxygen-rich air in its lungs before exhaling until all the oxygen is gone. Otherwise there might be problems.

Then, when the dragon breathes out, the CO₂ and triethylaluminum come into contact with the air, and ignite. As long as the dragon doesn't breathe in until the fire's gone, it isn't at risk of burning itself.

One other problem that comes up is how the dragon can keep the two pairs of lungs separate, when they're both connected to its trachea (windpipe).

Well, humans have this problem as well, in a way. Both the lungs and the stomach are connected to the back of the throat, but are kept separate by a flap called the epiglottis. We can assume that this would work for the dragons as well, although setting yourself on fire from the inside is rather more unpleasant than coughing if something goes wrong.

Now, could we extend this to other things as well? Apparently, many folktales involve dragons that breathe out ice or poison instead of fire.

Poison is easy, many different types of animals already can create poisons and toxins.

Ice is a bit more interesting, though.

There are several types of chemical reactions that are extremely endothermic--they take energy out of their surroundings when they react, so everything nearby becomes colder. This is how cold-packs work. The best one I found is 85 grams magnesium chloride hexahydrate, MgCl₂(H2O)₆ (commonly used to de-ice roads) and 100 grams ice. According to one source, this reaction can bring the solution to -94 degrees Celsius (-137.2 degrees Fahrenheit)!

So rather than the modified respiratory system, this frost-breathing dragon might have a structure in its mouth in which the magnesium chloride is created, and then it could trigger the reaction by chewing on a piece of ice or snow. Hopefully it could avoid frostbite in its mouth while breathing out. But at least keeping cool wouldn't be a problem.