John Dalton: A Life in Five Chapters

Chapter 1 · Teaching at Twelve

A Quaker education and a closed door

1766 – 1793 · Eaglesfield · Kendal · Manchester

John Dalton was born in September 1766 at Eaglesfield in Cumberland, to a Quaker family; his father was a weaver. The household was poor.

He was educated at the Quaker school and, at twelve, began teaching in it. At fifteen he moved with his brother Jonathan to run a Quaker school at Kendal.

At Kendal he met Elihu Robinson and then John Gough, a blind natural philosopher who had lost his sight to smallpox in infancy and who had nonetheless mastered Latin, Greek, French, mathematics and botany. Gough taught Dalton, who read to him and was taught in return — an arrangement Dalton described gratefully for the rest of his life.

As a Quaker he was barred from Oxford and Cambridge, which required Anglican subscription. He never attended a university and never held a university post. In 1793 he became tutor in mathematics and natural philosophy at the New College in Manchester, a Dissenting academy, resigned in 1800, and thereafter made his living giving private lessons.

He joined the Manchester Literary and Philosophical Society in 1794 and read almost everything he ever wrote to it — a provincial society of manufacturers and physicians, not a national institution.

He was a plain man in Quaker dress, unmarried, methodical to the point of eccentricity, and by every account not a good lecturer. On the day he was presented to the King he could not wear court dress, which is scarlet — forbidden to Quakers — and it was pointed out that as he was colour-blind he would see it as grey. He wore it.

“Chemical analysis and synthesis go no farther than to the separation of particles one from another, and to their reunion.”

— John Dalton, A New System of Chemical Philosophy (1808)

Why this matters

Dalton was excluded from the universities, worked outside every national institution, and read his atomic theory to a provincial society of Manchester manufacturers.

You have the schoolroom at twelve and the closed university door. What would you ask?

Ask Dalton

• “What is it like to teach at twelve years old?”
• “What did John Gough teach you?”
• “What did being barred from university cost you?”
• “Why read your work to a Manchester society rather than in London?”
• “Did your Quakerism shape how you worked?”

Chapter 2 · Fifty-Seven Years of Weather

Two hundred thousand observations, and where the atoms came from

1787 – 1844 · Kendal · Manchester · The Lake District

Dalton began a daily meteorological journal in 1787, aged twenty-one, and kept it until the day before he died in 1844 — fifty-seven years, something like two hundred thousand entries: temperature, pressure, humidity, wind, rainfall.

This was not a hobby alongside the chemistry. It is where the chemistry came from.

A weather-watcher has to think about the atmosphere. Why does water vapour rise into air? Why does air hold more moisture when warm? Why does dew form? Why do the gases of the atmosphere — nitrogen, oxygen, water vapour, carbon dioxide — stay mixed rather than settling into layers by weight, as they surely should if air were a continuous fluid?

His answer, published in 1801, is the *law of partial pressures*: in a mixture of gases, each gas exerts the same pressure it would exert if it alone occupied the container, and the total pressure is the sum of these.

That only makes sense if a gas is a *crowd of separate particles* moving in mostly empty space, each behaving as though the others were not there — not a continuous fluid.

And if different gases have different solubilities in water, and diffuse at different rates, then their particles must differ. His conclusion, stated in 1803: they differ in *weight*.

So the atomic theory arrives from meteorology. Dalton was trying to explain the atmosphere and had to invent atoms with weights to do it.

He also gave, in 1794, the first scientific description of colour blindness, from which he and his brother suffered — the condition was called Daltonism for a century. He left instructions for his eyes to be examined after his death; DNA analysis of the preserved tissue in 1995 confirmed he lacked the green photopigment.

Why this matters

Dalton's atomic theory came out of fifty-seven years of weather observation: he needed particles with different weights to explain why the atmosphere does not settle into layers.

You have the weather journal and the atoms that came from it. What is your question?

Ask Dalton

• “Why does the atmosphere not settle into layers?”
• “What does the law of partial pressures actually say?”
• “Why did the gases have to differ in weight?”
• “Why keep a journal for fifty-seven years?”
• “What did you see when you looked at a scarlet coat?”

Chapter 3 · Simple Whole Numbers

The claim that made a formula mean something

1803 – 1808 · Manchester

Dalton's atomic theory has four parts. Elements consist of atoms. All atoms of a given element are identical and share a characteristic weight. Atoms are neither created nor destroyed in a chemical reaction, only rearranged. And atoms combine in *fixed, simple, whole-number ratios* to form compounds.

The fourth is the load-bearing one.

Proust had established the law of *definite proportions*: a given compound always contains its elements in the same proportion by mass. Dalton added the law of *multiple proportions*: when two elements form more than one compound, the masses of one that combine with a fixed mass of the other are in a simple whole-number ratio.

His own example: carbon and oxygen. Take a fixed mass of carbon. In one compound it combines with a certain mass of oxygen; in the other it combines with exactly twice that mass.

Why exactly twice? Not 2.13, not 1.87. *Exactly* twice.

Because you cannot have a fraction of an atom. One carbon takes one oxygen, or one carbon takes two. The whole numbers in the mass measurements are a direct fingerprint of countable particles.

That argument converts a chemical formula from a summary of proportions by mass into a statement about *how many* of each atom are present. Every formula written since is that kind of statement.

He published the first table of relative atomic weights, taking hydrogen as one, and invented a system of circular symbols for the atoms — a circle with a dot for hydrogen, a solid circle for carbon — which was superseded by Berzelius's letters.

Why this matters

Whole-number mass ratios are the fingerprint of countable particles: you cannot have a fraction of an atom, so the arithmetic gives the atoms away.

You have the whole numbers and what they imply. What would you ask?

Ask Dalton

• “Why must the ratio be exactly two and not two-point-something?”
• “What does a chemical formula mean, on your account?”
• “How do you weigh something you cannot see?”
• “Why circles and dots rather than letters?”
• “What convinced you atoms are indivisible?”

Chapter 4 · The Rule of Greatest Simplicity

One assumption, and half the table wrong

1808 – 1830s · Manchester

To get an atomic weight from a mass ratio you need the *formula*. If eight grams of oxygen combine with one gram of hydrogen, the relative weight of an oxygen atom depends entirely on whether the compound is HO, H₂O or HO₂.

Dalton had no way to determine formulae, so he adopted a rule: assume the *simplest* possible. If only one compound of two elements is known, assume it is one atom of each.

So water became HO, and oxygen came out at about 8 rather than 16. Ammonia became NH, and nitrogen came out at about 5 rather than 14.

Many of his weights are consequently wrong, all for this one reason.

And the correction was available. Twice.

In 1808 Gay-Lussac showed that gases combine in simple whole-number ratios *by volume*: two volumes of hydrogen with one of oxygen give two volumes of water vapour. Dalton *rejected* this, partly because he distrusted the measurements and partly because it was awkward for his picture.

In 1811 Avogadro proposed that equal volumes of gases at the same temperature and pressure contain equal numbers of particles — which, applied to Gay-Lussac's result, gives water as H₂O directly. Dalton rejected this too, because it required that elemental gases exist as *pairs* of atoms bound together, and he could see no reason two identical atoms would attract each other.

That objection was reasonable, and it was wrong. It took until 1860, sixteen years after Dalton's death, for Cannizzaro to force the point through at the Karlsruhe congress.

Dalton had the right theory, the wrong numbers, and refused the two results that would have fixed them.

Why this matters

Dalton's atomic weights were wrong because of one simplifying assumption, and he rejected both results — Gay-Lussac's and Avogadro's — that would have corrected it.

You have the assumption and the two rejected corrections. What is your question?

Ask Dalton

• “Why assume the simplest formula?”
• “Why did you reject Gay-Lussac's combining volumes?”
• “What was wrong with two identical atoms joining?”
• “Would you have accepted it with better evidence?”
• “Does a wrong number damage a right theory?”

Chapter 5 · Forty Thousand People Filed Past

A plain Quaker with a state funeral

1830s – 1844 and after · Manchester

Dalton's later life was quiet and unchanged. He continued teaching privately, continued reading papers to the Manchester society, and continued the weather journal. He took a walk at the same time every day. He played bowls on Thursday afternoons.

He was elected to the Royal Society in 1822 without applying — he had been proposed without his knowledge — and received its first Royal Medal. He was elected a foreign member of the French Academy of Sciences, one of only eight. He was granted a government pension.

He had a stroke in 1837 and further strokes afterwards, which impaired his speech.

He made his last weather observation on 26 July 1844, in a hand barely legible, and died the following morning, aged seventy-seven.

Manchester gave him a civic funeral on a scale usually reserved for royalty. His body lay in state in the Town Hall and something like forty thousand people filed past. The procession included a hundred carriages, shops closed, and the route was lined.

That is a remarkable thing for a Quaker schoolmaster who never held a university post, and it says something about what an industrial city thought science was worth.

The unit of atomic mass — the dalton — is named after him. Atoms turned out not to be indivisible, and most of his weights were wrong, and neither matters much: what survived is the framework, that matter is made of countable particles combining in fixed whole-number ratios. Every chemical equation balanced by a school pupil is a Daltonian statement.

Why this matters

Forty thousand people attended the funeral of a Quaker schoolmaster who never held a university post, which says something about how an industrial city valued science.

You have the last entry in the journal and the forty thousand mourners. What would you ask?

Ask Dalton

• “Why did Manchester turn out like that for you?”
• “Atoms turned out to be divisible — does that undo your theory?”
• “What did you write in that last weather entry?”
• “Did you want to be elected to the Royal Society?”
• “What would you have done with a laboratory and a salary?”

What Dalton changed

Every chemical formula written today is a statement of the kind Dalton made possible: a fixed, whole-number ratio of countable particles. The unit of atomic mass is named after him, and the atomic theory is where school chemistry still begins — including the parts he got wrong, which are as instructive as the parts he got right. He also gave the first scientific account of colour blindness and the law of partial pressures.

A debate that continues

Dalton rejected both Gay-Lussac's law of combining volumes and Avogadro's hypothesis, either of which would have corrected his atomic weights, and the resulting confusion in chemical formulae was not resolved until Cannizzaro forced the point in 1860.

Keep exploring — ask Dalton

• “Which of your atomic weights troubled you most?”
• “What would have persuaded you about Avogadro?”
• “Is a simple assumption always the safest one?”

Related lives

• Amedeo Avogadro — Whose Idea Waited Fifty Years
• Joseph Louis Gay-Lussac — Who Went Up to Measure the Air
• Jöns Jacob Berzelius — Who Gave Chemistry Its Alphabet
• Antoine Lavoisier — Father of Modern Chemistry

Related themes

Atoms and atomic theory · Chemical formulae · Gases and pressure