by Harry Cliff
A few years later, in 1774, Priestley made the discovery that would secure his place in the history books. He found that when he focused sunlight onto a sample of highly toxic “red calx” (a mineral containing mercury) using a large burning lens, it gave off a new type of air that Priestley discovered would make a flame burn incredibly brightly and could keep a mouse in a sealed jar alive four times as long as normal. Priestley even tried the new air himself, writing,
The feeling of it to my lungs was not sensibly different from that of common air; but I fancied that my breast felt peculiarly light and easy for some time afterwards. Who can tell but that, in time, this pure air may become a fashionable article in luxury. Hitherto only two mice and myself have had the privilege of breathing it.
Priestley believed the miraculous properties of what he called “dephlogisticated air” were a result of it containing far less phlogiston than ordinary air. This allowed it to soak up the phlogiston released by a burning candle or a breathing mouse more effectively and thus keep them going for longer.
In October of that year, Priestley traveled to Paris, where he met many of the city’s brightest minds, including Antoine Lavoisier. Unfortunately, we know very little about their meeting, but it’s fun to imagine what these two chemical giants might have made of each other: the wealthy, self-confident, and urbane Parisian and the working-class radical with a strong Yorkshire accent. What we do know is that Priestley told Lavoisier about his new discovery, which proved to be the vital clue that he needed to complete his theory of fire. However, Lavoisier came to a radically different conclusion. Instead of dephlogisticated air, he realized that Priestley had in fact discovered the gas that combined with fuel during burning. He named it “oxygen.”
According to Lavoisier, fire wasn’t an element, and phlogiston didn’t exist. When a candle burned the fuel combined with oxygen to release carbon dioxide. Lavoisier showed that a similar process took place when animals breathed: carbon in their food combined with oxygen to release carbon dioxide and heat. He even demonstrated this idea using a guinea pig placed in an empty bucket surrounded by a container full of ice. The heat from the rodent’s body melted the ice, and by measuring the amount of water that ran out of the bottom of the container Lavoisier was able to figure out how much heat it was giving off, proving that animals effectively burned their food to create heat. Don’t worry, the guinea pig escaped freezing to death—though it definitely would have gotten a bit chilly—and has the possibly dubious honor of being the original source of the term “to be a guinea pig.”
Lavoisier wasn’t done with his revolution yet. People had noticed that when Cavendish’s inflammable air was burned with oxygen, water seemed to be left behind. Lavoisier became convinced that this meant that water, once thought to be the most basic of all the elements, wasn’t an element either. Instead it was made from this inflammable air, which he renamed “hydrogen,” and Priestley’s oxygen.
Most of the scientific community, particularly in France’s great imperial rival Britain, found it hard to swallow Lavoisier’s radical new ideas. Priestley rejected Lavoisier’s suggestion that water wasn’t an element and clung to phlogiston theory for the rest of his life. Lavoisier needed firm experimental proof to swing people behind his new chemistry. He finally provided it in spectacular fashion by splitting water into oxygen and hydrogen in a public demonstration held at his laboratory in 1785.
By the late 1780s the old classical elements lay in ruins. Water could be broken apart into hydrogen and oxygen, air was a mixture of different gases, and fire was a process of combining oxygen with fuel. In 1789 Lavoisier published his greatest piece of propaganda for the new chemistry: a textbook called Traité élémentaire de chimie (An Elementary Treatise on Chemistry). In it, he gave his new definition of a “chemical element,” a substance that couldn’t be broken down into anything else. What’s more, he provided a list of thirty-three of these new chemical elements, many of which we still recognize today, including oxygen, hydrogen, and azote, or what we would now call nitrogen. The treatise became one of the most influential books in the history of science and within a few years all but his most die-hard critics had been won over. Lavoisier had lived up to his arrogant claim; he really had brought about a chemical revolution.
So what might Lavoisier have made of the three products of my apple pie experiment? First of all, I suspect he would have been rather unimpressed by my rough and ready approach to chemistry. My dad’s garage isn’t quite as well equipped as Lavoisier’s lab and I didn’t have any kit that would have allowed me to precisely weigh the apple pie before and after the experiment as Lavoisier surely would have done. Worse still, I’d carelessly allowed the white mist to escape, meaning that its composition would have to remain a mystery.
But what of the charred black hard stuff left behind in the test tube? If we take a look at Lavoisier’s list of chemical elements one jumps out immediately: charcoal. Charcoal has been used as fuel for centuries and was often made by burying piles of wood under a layer of turf and lighting a fire in the center. The turf kept the air out, preventing the sides of the woodpile from catching on fire, while the intense heat from the central fire broke the wood down into charcoal and gases. This is more or less what we had done with the apple pie; the bung in the test tube had acted like the turf, stopping the oxygen in the air from getting in and preventing the super-heated pie from catching fire. We had made charcoal. Or what in modern terms is a fairly pure form of the basic element of all organic matter: carbon.
As for the yellowish liquid, well, in principle I could have tried to break it down further, but unfortunately I’d only been able to generate a thimbleful of the foul-smelling liquid—far too little for the experiment to work—and I wasn’t about to empty my local supermarket of apple pies and spend days bubbling them down. Anyway, it seems a safe bet that it was mostly water and thanks to Lavoisier we know that water is a compound of oxygen and hydrogen, giving us another two ingredients. Indeed, carbon, oxygen, and hydrogen between them are the dominant chemical elements in all organic matter, from apple pies to humans. However, they are certainly not the only chemical ingredients. A quick glance at the nutritional information on the back of the box tells me that they contain at least some iron, which was probably still mixed up in the charcoal. And although I couldn’t isolate them in my dad’s garage, there’s also nitrogen, selenium, sodium, chlorine, potassium, calcium, phosphorus, fluorine, magnesium, sulfur, and probably many more—perhaps only in very tiny amounts, but they’re there.
The deeper question though is this: What are these different chemical elements made of themselves? After all, if we really want to make an apple pie from scratch, hydrogen, oxygen, and carbon won’t cut it. They are just the start of the story.
Skip Notes
*1 In fact, the Russian polymath Mikhail Lomonosov had discovered the law of the conservation of mass in his own experiments many years earlier, but Lavoisier’s tremendous influence over the development of modern chemistry means that poor old Lomonosov is mostly forgotten.
*2 People who studied the natural world were known as “natural philosophers” until well into the nineteenth century, when the word “scientist” first started to be used.
*3 Priestley never made any money out of his invention, but his technique was later taken up by J. J. Schweppe to make carbonated mineral water, founding the Schweppes Company in Geneva in 1783.
CHAPTER 2
The Smallest Slice
At the start of Cosmos episode 9, just after uttering the immortal phrase that inspired this book, Carl Sagan gets up from his seat at the head of the grand table and picking up a knife poses us a question: “Suppose I cut a piece out of this apple pie…and now suppose we cut this piece in half, or more or less, and then cut this piece in half, and keep going…How many cuts before we get down to an individual atom?”
Ten? A h
undred? A million? Perhaps you can keep cutting up the apple pie forever into ever smaller and smaller pieces, until you have an infinity of infinitesimal slices. This neat little thought experiment captures the essence of the most powerful idea in science—that everything is made of atoms.
Atoms, according to the classic definition, are tiny, indestructible nuggets of matter that can’t be changed or broken apart (the word “atom” comes from the ancient Greek atomos, meaning “uncuttable”). They come in different shapes and sizes and combine to create everything we see in the world around us, from apple pies to astronauts. It’s a beguilingly simple idea and yet at the same time goes completely against our everyday experience. Our senses reveal a world of form and color, texture and temperature, taste and smell: the smooth red skin of an apple or the bitter taste of coffee.
Atomic theory tells us that this world is an illusion. Deep down at the roots of things there is no such thing as the color red or the taste of coffee. Deep down there are only atoms and empty space. Color, taste, heat, texture are all tricks of the mind that emerge from uncounted multitudes of different atoms, bound together in a dazzling array of different forms.
When you think about atoms this way it’s not surprising that the idea took millennia to take hold. Although versions of atomic theory appeared in ancient Greece, they never really gained much traction, particularly as the influential Aristotle dismissed the idea, preferring to trust his senses over abstract thinking. The theory of qualities makes far more sense; we’re all familiar with hotness, coldness, dryness, moistness, but who of us has ever seen an atom?
It was only in the seventeenth century that atoms started to be taken seriously in scientific circles. Isaac Newton was an avowed atomist and believed that atoms not only made up the material world but even light itself, which he imagined as a shower of tiny particles or “corpuscles.” Newton’s mighty legacy to science, along with gravity, optics, and the laws of motion, included persuading many eighteenth-century natural philosophers to take an atomic view of the world. That said, there was precious little evidence for atoms’ existence, and the concept was pretty useless for understanding chemistry. Lavoisier and Priestley could experiment and theorize without having to worry very much about what was going on deep down. Lavoisier, a stickler for going only where facts led him, had little time for invisible atoms.
Before atoms could be brought into the light of day, someone was going to have to build a bridge between their hidden realm and the world of chemistry. That person emerged from the wild and beautiful county of Cumberland in the northwest of England. His name was John Dalton.
IMAGINING ATOMS
John Dalton was born in 1766 in Eaglesfield, a small village surrounded by low rolling farmland in a remote part of northwest England. John’s upbringing was decidedly modest; his father Joseph was a weaver by trade and the family owned and farmed a small strip of land near the village.
However, young John had a couple of advantages. First off, he was an unusually bright and precocious little boy, with a natural curiosity and the ability to soak up information like a sponge. Second, his family were Quakers, religious nonconformists who set a high value on learning. John’s mother in particular encouraged his education and used the family’s network among the Society of Friends to provide her son with a better schooling than a poor farm boy would normally have gotten in eighteenth-century England.
John developed an early fascination with the weather, which isn’t surprising as there’s a lot of it in the northwest of England. From his home he could watch rain clouds rolling in from the Irish Sea and passing over the dramatic peaks of Grasmoor and Grisedale Pike. The Quakers weren’t exactly a fun-loving bunch—they were teetotalers and emphasized holy behavior in all they did—but studying nature was one of the few permitted leisure activities, regarded as a way of revealing God’s work in the world. As a boy John began to take daily readings of air pressure, temperature, humidity, and rainfall, a routine he followed until the day he died, and though he had no idea at the time, it was the beginning of a long journey that would eventually lead him to a theory of atoms.
Although John’s education was supported by the Quakers, his situation was often precarious, and by the age of fifteen he was forced into agricultural labor to make ends meet. The future looked bleak, but salvation came with an invitation to teach at a Quaker boarding school fifty miles away in the market town of Kendal. The Quakers had generously equipped the school with a suite of scientific instruments that he was quick to start experimenting with. He also acquired a much-loved tutor in the blind natural philosopher John Gough, who took a shine to the eager teenager and taught him mathematics and science, including Newtonian atomic theory. In return, John helped his blind mentor with reading, writing, and drawing diagrams for his scientific papers.
John had ambitions to study law or medicine but was barred from English universities because of his religion. Instead he eventually secured a position as a professor at a new college that had been set up by religious nonconformists in the booming industrial town of Manchester.
To the farm boy from Eaglesfield, Manchester was a huge and bustling place. Here, religious and political radicalism, new scientific ideas, and revolutionary technologies were driving change at a pace that was dizzying, perhaps even frightening. Manchester was the beating heart of an industrial revolution that was transforming Britain into the powerhouse of the world. Towering new cotton mills powered by smoke-belching steam engines and row upon row of redbrick terraced houses were rising on the city’s skyline. Here science wasn’t a hobby carried on by wealthy aristocrats in their private labs, but part of a thriving community of engineers, craftsmen, and industrialists. Dalton couldn’t have come to a better place and dived headfirst into Manchester’s larger scientific pond.
The weather remained his obsession, in particular, rain. It’s a long-standing joke among southerners (like me) that it’s always raining in Manchester. That may be a little unfair, but there is certainly no shortage of moisture in the northwest. Dalton would take long walking holidays in his much-loved but decidedly drizzly Lake District, where the air sometimes feels so heavy with water that you wonder if it could soak up any more. In fact, it was just this question that got him thinking about atoms.
Dalton began to do experiments to see how much water vapor a fixed volume of air could absorb. At the time, people thought that water dissolved in air, like sugar dissolves in a cup of coffee. If you add more than around 150 teaspoons of sugar to a cup of coffee—which I think is even more than you get in a Starbucks Cinnamon Dolce Latte—then it stops dissolving and you end up with sugar granules rolling around at the bottom of the cup. A similar thing happens when it rains: when the air is completely saturated with water vapor the water condenses into little droplets, which form clouds, and if the droplets get big enough it starts to rain.
However, if there is more air squeezed into a given volume, then it should be able to soak up more water vapor. It’s a bit like adding more coffee to your mug to dissolve those extra sugar granules. However, Dalton’s experiments showed something truly weird: a container would always absorb the same amount of water vapor regardless of how much air was squeezed into it. It seemed as though the air and the water vapor somehow ignored each other, occupying the same space but without interacting.
What has all this got to do with atoms? I hear you cry. Well, it all comes down to the interpretation. Dalton took this result as evidence for the idea that air and water vapor only exert forces on atoms of their own kind. Two atoms of air would interact with each other, and two atoms of water vapor would interact with each other as well, but an atom of air and an atom of water vapor would totally ignore each other. It’s a situation similar to the slightly awkward birthday parties I’d find myself at in my early twenties. There would usually be two groups: the birthday girl or boy’s old high-school friends and the newer university friends. Although we we
re all at the same party, we would drift around the room chatting within our respective cliques and barely acknowledge the existence of these other friends. According to Dalton, atoms of two different gases behave in more or less the same way.
Dalton published his theory in 1801, and it immediately caused a stir that spread beyond Manchester to the scientific academies of continental Europe. In London, the charismatic chemist and inhaler of strange gases Humphry Davy was intrigued by his theory of “mixed gases,” but many leading scientists argued passionately against it, including his old mentor and friend, John Gough, which must have stung a little.
Dalton was determined to prove his critics wrong and set out on a series of experiments that he hoped would provide irrefutable evidence for his theory. Along the way he became interested, almost by accident, in the problem of why certain gases dissolve in water more easily than others. His solution was simple but held the seeds of what would become a fully fledged atomic theory. Dalton argued that it was the weight of the atoms that determined how easily they dissolved, with heavier atoms dissolving more easily than light ones. To test this idea, he somehow had to figure out how heavy different atoms were compared to one another.
But how? Remember that no one had even gotten close to seeing an atom in the early nineteenth century. It would be almost two hundred years before a microscope would be invented that was powerful enough to image one. Atoms were just an idea and if they existed at all were so fantastically minuscule that almost every scientist of the day thought they would lie forever beyond our perception. How on earth could Dalton possibly measure their masses?
