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We sat down with Sam Kean to talk about his book Caesar's Last Breath and how the chemistry of atmospheric gases can be so darn interesting.

The book explores the classic chemistry question: are you breathing some of the same air molecules that were expelled by Julius Caesar's dying exhalation?

It's something you simply can't work out exactly without knowing a ton of data: Caesar's exact lung capacity, the composition of the air in ancient Rome, atmospheric circulation from March 15th, 44 BCE, to today and...stop, stop, I'm getting a headache.

Instead, you treat it as what we call a Fermi problem.

Physicist Enrico Fermi had a knack for working out rough estimates that weren't right, but close enough to give you a general idea.

Using Fermi's close-enough style of logic, what do you get?

"Are we breathing Caesar's last breath?"

"So, yes we are, actually, breathing...PARTS of Caesar's last breath."

"Each person, when you breathe, it's about a half a liter to a liter."

"In the book I mention the exact amount, but it's like a zero point nineteen zeroes, that's the percentage that one breath is compared to the entire atmosphere, so a minuscule amount."

"On the other hand, if you look at how many molecules, gas molecules, are actually in a liter, at you know, room temperature, it's some gargantuan number, it's like 25 sextillion, which is a 25 with 21 zeros after it.

So it's a huge, like an unfathomably large number.

"So the question becomes, well, which number's gonna win?

The tiny number, which is how big a breath is compared to the atmosphere, or the really BIG number, which is how many molecules are in a single breath?

And when you go through all the math, crunch all the numbers, it turns out that they cancel almost exactly, and you end up with on average about one molecule of Caesar breath in every breath that we take."

Fermi estimation is pretty fun, if you ask me, because you can come up with answers you should in no way be able to find the answer to -- like whether you're sharing air with Caesar.

But why him?

Why not Joan of Arc or Madame Curie or Tessa Thompson?

"He's become for some reason the default person that you hear with this problem, I dunno why someone fixated, I'm sure back in the days when they were studying classics all the time..." "But even, you know, two to three years, the atmosphere has enough turbulence, it mixes enough, where those molecules would be fairly evenly spread over the entire world.

So yes, Shakespeare, Amelia Earhart, Winston Churchill, Confucius, you have a connection with their breath as well."

But it turns out Caesar's last words provided enough inspiration for a whole book on what the atmosphere's made of.

"I think what I was a little surprised about was just the variety of different gases that you do see in the atmosphere.

You see, uh, refrigerants, you see little bits of anesthesia, you see all the noble gases in there.

Argon is roughly one percent of the atmosphere."

We've treated the atmosphere pretty badly, what with all the climate change and the aforementioned refrigerants poking holes in the ozone layer and all that stuff.

Is there any good news?

"There's good news coming out about the atmosphere, things like acid rain, we have not eliminated, but it's much less of a concern than it used to be."

"Yes, I remember being absolutely terrified when I was growing up, and learning about it and I don't think I've ever actually...witnessed it."

"Yeah!

No, but it does sound so awful!"

"Oh, my God, acid falling out of the sky!"

Yeah, it seems like we're pumping less of the bad stuff that creates acid rain into the atmosphere.

So even though my elementary school textbooks made me afraid to go outside in so much as a light shower, we've made real progress in that department.

It sometimes still happens, and natural habitats damaged by acid rain will need more time to mend.

But they are on the mend.

But here's an even weirder story from the book... the story of Einstein's lost refrigerator.

The tale goes that Einstein -- yeah, that Einstein -- was enjoying his morning cup of coffee when he read a tragic story in the paper.

Refrigerants at the time could be pretty toxic, and an entire family had perished when their refrigerator sprung a leak.

So Einstein called up fellow physicist Leo Szilard and got to work.

"They set out to build a better refrigerator.

And they tried to make a whole new type of refrigerator, one that didn't use electricity, it didn't have a motor, it was more based on evaporating and cooling gases and mixing different gases in various clever ways to basically take heat, move it around, you know, do different things."

Unfortunately, the Einstein fridge never took off, because somebody came along and invented Freon right then.

And fridges based on CFCs were a bit cheaper and easier to make than Einstein and Szilard's design.

They just...also wrecked the ozone layer.

"Imagine being the chemist who scooped Einstein."

"Yeah, it was actually a man named Thomas Midgley.

He was kind of well known because he invented not only chlorofluorocarbons, he invented, uh, leaded gasoline as well."

"oooh, unfortunate ..." "Unfortunately two of the worst ideas of the 20th century."

That's a pretty terrible track record.