The 18th-Century Quaker Farmboy Who Laid the Groundwork for Atomic Theory
Harry Cliff on How John Dalton Contributed to the Most Powerful Idea in Science
At the start of Cosmos Episode Nine, just after uttering the immortal phrase that inspired my latest 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 until we get down to an individual atom?”
Ten? A hundred? 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 17th 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 18th-century natural philosophers to take an atomic view of the world. That said, there was precious little evidence for their existence. In fact, the idea of atoms was pretty useless for understanding chemistry. Lavoisier and Priestly 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.
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 18th-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 rainclouds rolling in from the Irish Sea and passing over the dramatic peaks of Grasmoor and Grisdale Pike. The Quakers weren’t exactly a fun-loving bunch—they were teetotallers 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, 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 15 he was forced into agricultural labour to make ends meet. The future looked bleak, but salvation came with an invitation to teach at a Quaker boarding school 50 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 farmboy 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 about 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 in Manchester’s larger scientific pond.John had ambitions to study law or medicine but was barred from English universities because of his religion.
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 North West. 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 thought 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, in a similar way to how 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 Latté—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 the air has a higher pressure—in other words, if there is more air squeezed into a given volume—then it should be able to soak up more water vapor. It’s 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 drinks 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 were 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 19th century. It would be almost 200 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 miniscule that almost every scientist of the day thought they would lie forever beyond our perception. How on earth could Dalton possibly measure their masses?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.
Dalton’s stroke of brilliance was to take his theory of mixed gases—that atoms only repel other atoms of their own kind—and extrapolate it to figure out how many atoms of different chemical elements bind together to make molecules. His reasoning went something like this: imagine that two atoms of two different chemical elements, let’s call them atom A and atom B, bind together to make a molecule A-B. Now, imagine that another atom of A comes along and wants to join the party. Since atoms of A repel each other it will naturally want to get as far away from the other A-atom as possible and so attach to the opposite side of the B-atom to make a larger molecule A-B-A. Then if a third atom of A comes along this time it will arrange itself at 120 degrees from the other two atoms of A to form a triangular shape with B at the centre, and so on.
Dalton reasoned that if only one compound of A and B is known, then its molecule should have the simplest structure, which is AB. If there are two different compounds of A and B then the second molecule will be the next simplest, ABA.
For example, two different gases made of carbon and oxygen were known in the early 19th century: one was called “carbonic oxide” (the colorless toxic gas that nearly killed Humphry Davy when he breathed it in, possibly in the name of science or in search of another way to get high) and what was called “carbonic acid” (the “fixed air” discovered by Joseph Black, which was used to suffocate a number of unlucky mice, again in the name of science). By weighing the amount of oxygen that reacted with a fixed amount of carbon to make these two gases, Dalton found that carbonic acid contained twice as much oxygen as carbonic oxide. Applying the rules of his atomic theory, this meant that carbonic oxide was the simplest molecule, made of one carbon and one oxygen atom—what we now know as carbon monoxide (CO)—and carbonic acid contained one carbon and two oxygen atoms—or in modern terms, carbon dioxide (CO2).
At last, Dalton could figure out the relative masses of carbon and oxygen atoms, calculating that an oxygen atom weighs about 1.30 times more than a carbon atom, which is remarkably close to the modern value of 1.33. Through a combination of guesswork, theorizing and experimentation, he had measured a property of an atom, and in doing so, had caught a glimpse of their hidden realm for the very first time.
Dalton knew that he was onto something big. He completely forgot about the original problem of dissolving gases in water and engrossed himself in his new atomic theory. After around three years of work, interrupted by heavy teaching duties and the occasional walking holiday in his beloved Lake District, he was ready to reveal his ideas to the world.
Excerpted from How to Make an Apple Pie from Scratch: In Search of the Recipe for Our Universe, from the Origins of Atoms to the Big Bang by Harry Cliff. Used with the permission of Doubleday Books. Copyright © 2021 by Harry Cliff.