An Ocean of Air (7 page)

But although he disliked the system of taxation in part for moral reasons, he was at least as troubled by the absurd inefficiency of overtaxing some people almost to the point of extinction while letting others off completely. Any sort of inefficiency pained him. Lavoisier dealt with his financial affairs with the same careful precision that he was to accord his scientific experiments: Unlike most of his compatriots in the Ferme, he recorded every transaction and accounted for every sou.

Lavoisier's work with the Ferme took up almost all his time, but very little of his creative energy. He was still fired with an ambition to achieve something more remarkable than just making money, and he began to work exhaustively to find a subject worthy of his scientific attention. He conducted his research from six to nine each morning and seven to ten each evening, and in addition devoted one full day a week, his
jour de bonheur
(day of happiness), to his favorite activity.

Meteorology held his attention for a while—he had been taking daily barometric measurements for several years and continued to do so for most of his life—but it didn't have quite the spark he was seeking. Then, after performing an expensive experiment to prove that diamonds are combustible, Lavoisier began to wonder why some materials burn while others don't.

He was aware of the prevailing theory of phlogiston, but he wasn't convinced by it. To most natural philosophers of the time, Priestley included, phlogiston was a very sensible concept. If you watch something burning, it's easy to believe that the flames are releasing some substance from inside the material, and that the more of this substance—phlogiston—it contains, the more easily it burns.

However, Lavoisier was troubled by the undeniable fact that when many substances, iron for instance, are heated in air they become not lighter, but heavier. Until then, theorists had fudged the answer to this mystery by declaring that phlogiston must have some kind of negative weight, so that losing it makes you heavier. To Lavoisier, that seemed like nonsense. If something gains weight when it burns, he reasoned, it must surely be absorbing rather than releasing something. The question was, what?

To try to find out, Lavoisier began to study the work of every natural philosopher he could find who had worked on the problem, including that of Priestley. Lavoisier spoke no English, but his young wife was very proficient at languages and spent much of her time translating for her husband. She had every reason to be grateful to him. At the age of fourteen she had been troubled by a proposal of marriage from a wealthy and powerful man in his fifties who had seemed to her like an ogre. Lavoisier, then age twenty-eight, who knew her father and was already fond of her, had rescued her from a horrible fate by the simple expedient of marrying her himself.

Lavoisier was impressed with the breadth of Priestley's investigation. He described it as "most painstaking and interesting work." But he was disgusted by Priestley's chaotic style of investigations, and the way that he raced from one topic to another with little thought as to what might connect the whole. Priestley's work, said Lavoisier, "consists more or less of a web of experiments, almost uninterrupted by any reasoning."

And that was where Lavoisier saw his chance. He knew his brain was at least as brilliant as the chaotic and passionate Priestley's. But Lavoisier had something else as well—the cool head and precise habits of a financier. Put these together and he could achieve what nobody had done before. He could find out not just what happens when something burns, but why.

So, shortly after his marriage, Lavoisier began a series of meticulous experiments. First, he confirmed what he and everybody else already knew. He carefully weighed various materials such as phosphorus and lead, burned them in common air, and measured the weight of the ash that was left. Every time he tried this, the ash was heavier than the material he had started with. This was just as he had expected.

However, Lavoisier's next experiment was much more ingenious. He placed some lead on a balance inside a glass jar full of air, which he sealed. Then he carefully weighed the entire jar, lead, balance, and all. Next, he heated the lead from the outside and watched as the balance gradually tipped to show the lead gaining its weight. Finally—and this was the clever part—without opening the jar he weighed it again. Even though he could look through the glass walls and see from the tipped balance inside that the lead had grown significantly heavier, the weight of the entire jar remained exactly the same. Whatever had caused the lead to gain weight must have come from inside the jar.

It seemed unlikely that the extra weight had come from the glass walls or the balance. The most obvious source was the air. But how to prove it? Lavoisier reasoned that if some of the jar's air had disappeared into the lead, it must have left a gap, a partial vacuum waiting to be filled. So he unsealed the jar and sure enough, air from the outside rushed in to fill the gap. And then he weighed the vessel again to see how much new air had entered. The answer: precisely the same amount as had disappeared into the lead.

It was in the very precision of his measurements that Lavoisier had started to find his answers. Many people had burned one material with another, weighed them in a desultory fashion, and surmised what might be happening. But Lavoisier of the tidy mind and precise habits was the first to put it all together into a quantitative whole. The lead increased in weight by this amount. The air above it lost this quantity. Since the two values are precisely the same, a portion of the air must have gone into the lead. And since the remainder of the air turned out to be incapable of supporting further burning, the missing air—about a fifth—must be different from the rest.

This was momentous news. Lavoisier had discovered that common air was not a single indivisible element; instead, it was clearly a mixture of other things. And one of them, making up about one-fifth of its bulk, was the mysterious and powerful substance that allowed materials to burn, and combined with them in the process.

But, frustratingly, Lavoisier still didn't know what this substance actually was. He could watch it disappear from common air but couldn't make it reappear. Once lead has burned and taken up its oxygen, it won't release it again no matter how much you heat it. Lavoisier managed to make the lead ash and other calxes yield fixed air, by burning them with charcoal, but he couldn't retrieve the exact gas that they had taken up from common air in the first place. He needed to get at the air trapped inside his lead in order to release it and study it and discover what it was, but it remained stubbornly locked away.

Lavoisier knew he needed to find another material, one that would soak up the mysterious ingredient from the air when it was heated but would release it afterward. Lead wouldn't do this, nor would sulfur or tin or any of the other materials Lavoisier tried. For the moment at least, he was stumped.

Then, in October 1774, Lavoisier learned that Priestley himself was in town. Priestley was in the middle of a tour of European countries with his patron, Lord Shelburne, and Paris was their latest stop. Priestley wasn't much impressed with the city. Though its buildings were undoubtedly beautiful, parts of the city remained positively medieval. Foul-smelling open sewers ran down the centers of what, some hundred years later, would become the city's elegant boulevards, and there were none of the sidewalks that already graced London's streets. With a provincial Englishman's disregard for foreigners, Priestley also decided that many of the people he met were "too much taken up with themselves to admit of that minute and benevolent attitude to others, which is essential to politeness."

In spite of these criticisms of the Parisians and their habits, which might have had more to do with his indifferent French than any real impoliteness, Priestley was lionized throughout the city. Though news of his experiment with
mercurius calcinatus
had not yet filtered out, since he had performed it just a few months earlier, his previous work on the new airs was known throughout Europe and he was already famous. By now Lavoisier was considered France's foremost natural philosopher, and a meeting between the two was inevitable. Thus one evening that autumn, the Lavoisiers invited Priestley to dine at their house along with most of the city's resident intellectuals. And naturally enough, during the course of the evening, stammering in poor French that was occasionally supplemented by Madame Lavoisier's helpful translation, Priestley told Lavoisier about his experiment.

He told how he had made the
mercurius calcinatus
by burning mercury in air until the silver liquid turned into a crumbling red powder, and then how he had trapped this powder in his tube of mercury and heated it with his precious burning glass until it spewed out a mysterious new air that caused candles to burn with a dazzling, incandescent light. It was almost as if the
mercurius calcinatus
had trapped within it the essence of fire.

Lavoisier was riveted. Could this finally be the material he was looking for? When Priestley left, he dropped his useless lead and tin and started work on
mercurius calcinatus.

First, Lavoisier took four ounces of very pure mercury and put it in a closed glass vessel with fifty cubic inches of common air. Then he heated it almost to its boiling point and kept it that way for twelve days. At the beginning, nothing much happened. But gradually red specks began to appear on the mercury's silver surface, and they grew larger each day. By the end of the twelve days, the reaction seemed to be at an end. Lavoisier had lost nine cubic inches of air and gained forty-five grains of red
mercurius calcinatus.
The air left behind in the vessel would not permit a candle to burn, but unlike fixed air it did not turn lime-water cloudy. This was some other form of air that apparently existed only to dilute the vibrant, active part.

With the utmost care, Lavoisier collected the forty-five red grains and put them in a small glass jar whose long, thin neck twisted around itself
several times and then poked up into a bell jar full of water. Now all he had to do was heat the grains of
mercurius calcinatus.
As he did so, out and up bubbled the very air they had trapped within them. Exactly nine cubic inches made their way into the bell jar above. As a final proof, Lavoisier took this air and recombined it with the stuff that had been left behind from the first experiment, the stuff that would not support burning but would neither turn lime-water cloudy. Immediately this mixture became indistinguishable from common air. Candles burned normally in it; animals breathed happily for exactly as long as you would expect.

Lavoisier had found the magic ingredient, the active part of the air. He had extracted it, trapped it inside mercury, released it, and recombined it with the passive part to regenerate common air. By applying his painstaking system of accounting to science, he had looked into the heart of a flame. He now knew what fed every fire on Earth.

But what to call it? Lavoisier had no patience with Priestley's name for this new gas, "dephlogisticated air." His experiments had clearly proved that burning had nothing to do with phlogiston and everything to do with the presence or absence of this one crucial active ingredient. Instead, since it seemed to be trapped in many different kinds of acid, he named it "oxygene," which means "acid-born."

Lavoisier was intrigued with his new gas and began to work on it in earnest. In particular he wanted to know more about the relationship between burning and breathing, and the role that oxy-gene might play in each. Like Priestley, Lavoisier had noticed the similarity between these two processes. Place a burning candle in a closed jar of common air and eventually the flame will sputter and die. Place a living mouse in such a jar and after a while the animal will no longer be able to breathe. To Priestley, both candle and mouse were giving out phlogiston. To Lavoisier, both were using up oxy-gene. And now, he wondered how far the similarity between the two processes went. How could the same substance that fed a flame also feed life itself?

Until now, nobody had made any truly systematic investigations into the nature of breathing. Obviously, it was necessary for life. And just as obviously, food somehow sustained life. But there was no sense that food in a
person was like fuel in a machine. Aristotle had believed that the purpose of breathing was to cool the blood, and this was still a popular notion even in Lavoisier's time. Other philosophers thought that breathing in a confined space became increasingly difficult because it reduced the elasticity of the air, which prevented it from pushing back enough to inflate the lungs properly. As to what relationship this had to eating, nobody really knew.

So, Lavoisier began his experiments. Unusually for him, he performed them with a collaborator, a young mathematical genius named Pierre-Simon Laplace. Among his other achievements, Laplace would later produce the complex equations that govern the behavior of the solar system, and it is sometimes said that his efforts in this regard were halted because his equations were so successful at accounting for the available facts that until more observations could be made, there was nothing left to explain. Laplace was already famous, the most talented mathematician in the known world, and together he and Lavoisier devised a series of experiments to understand the nature of breathing.

For their experiments they used small hairy rodents lately returned from the jungles of South America. These "guinea pigs" were very convenient in the laboratory, wrote Lavoisier, because they were "tame, healthy creatures, easy to feed and big enough to inspire and expire air in quantities suitable for measurement." Lavoisier had designed a clever piece of apparatus to discover the relationship between the amount of oxy-gene these guinea pigs consumed and the heat they gave off. The heat was the hard part. Lavoisier had decided to measure this by the melting of ice. He made a large sealed circular chamber comprising three concentric rings. The innermost ring contained the guinea pig, the second ring was packed with a known quantity of ice, and the outermost ring was filled with snow to prevent the heat of the room from reaching the ice and melting it. Lavoisier and Laplace set out to monitor what happened first when the guinea pigs were at rest, and then when they became steadily more active.