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The history of Earth’s atmospheric gases is a provocative and entertaining read, writes Robin McKie.
CAESAR’S LAST BREATH
The Epic Story of the Air Around Us
The Scottish physician Joseph Black was responsible, in 1764, for one of science's more unusual chemical experiments. He had already achieved fame by becoming the first scientist to isolate a pure gas: carbon dioxide, known as "fixed air'' at the time. Now Black was anxious to further his work by demonstrating that the gas was exhaled by human beings.
So he looked for a place where respirations would be at their most intense and accessible - and decided that the kirk best fitted the bill. Presbyterianism in 18th-century Scotland was, if nothing else, a source of plentiful hot air. So Black, who was then Glasgow University's professor of anatomy and chemistry, placed a solution of limewater inside an air duct in a church where it was said that more than 1500 people would remain at their devotions for 10 hours on one winter's day. (Glaswegians have always taken their religion seriously, it should be noted.)
Limewater produces a white precipitate of calcium carbonate when it is exposed to carbon dioxide - and sure enough, when Black examined his solution after the parishioners had staggered home, he found that it was impregnated with substantial amounts of white chalky precipitate. Exhaled air, enriched with carbon dioxide, had made a profound chemical impact on his solution.
Thus Black concluded that the air we breathe is altered by our bodies' chemical processes, a key breakthrough that showed how human physiology relies deeply on Earth's atmosphere for sustenance and survival, a point stressed by Sam Kean at the beginning of this absorbing, entertaining examination of the air around us. "You can survive without food, without solids, for weeks,'' he points out. "You can survive without water, without liquids, for days. But without air, without gases, you'd last a few minutes at most.''
The crucial importance of air was unappreciated in Black's time, and although we are better informed today, we still take it for granted, argues Kean.
Hence Caesar's Last Breath, in which he attempts to correct this imbalance by highlighting how our complex atmosphere evolved as Earth cooled from being a superhot, volcanically active protoplanet 4.6 billion years ago to a temperate blue world that is now surrounded by a life-supporting shell of oxygen and other gases.
We also learn about the remarkable men and women who transformed our knowledge about the air that we breathe.
Black was a major player in this work, as were his pupil Daniel Rutherford, who first isolated the nitrogen that forms 78% of our atmosphere, and Henry Cavendish, who discovered hydrogen and showed it was a constituent of water. Joseph Priestley followed this up by discovering nine new atmospheric gases, while engineers like Thomas Newcomen and James Watt launched the Industrial Revolution by using their understanding of gases and atmospheric pressure to create huge steam-powered engines.
Other key protagonists in this procession of gaseous geniuses include Le Petomane, the stage name of the French flatulist - ie, professional farter - Joseph Pujol, who astounded 19th-century Parisian nightclub audiences with his impressions - which emanated from his rear end - of farmyard animals and musical instruments as well as a rousing rendition of La Marseillaise.
It is an unusual way to explore history, to say the least, though Kean is insistent that the air we inhale directly entangles us with the past. "Some of the molecules in your next breath might well be emissaries from the fall of the Berlin Wall or witnesses to World War 1,'' he claims. Indeed, it is possible that your next breath might include some of the molecules of air that Julius Caesar exhaled when he was assassinated in 44BC, he suggests.
It sounds unlikely, though Kean is convinced. Consider the arithmetic, he argues. Caesar's final breath - exhaled as he was stabbed to death in the senate - would have contained about a litre of air made up of about 25 thousand million million million molecules.
At the same time, a litre of air represents 0.000000000000000000001% of all the air on Earth. When you crunch these numbers, says Kean, you will find that roughly one particle of the last air that was breathed out by Caesar more than 2000 years ago will appear in your next breath. "Across all that distance of time and space, a few of the molecules that danced inside his lungs are dancing inside yours right now.''
It is provocative but compelling stuff, written with verve and in a style that veers between simple lightheartedness and open jocularity. (The emergence of Earth's first atmosphere, from early volcanic eruptions, is described as the Big Burp, for example.) Purists may groan, but the overall effect is eminently accessible and enjoyable. A real gas, in short.
- Guardian News and Media