John Dalton

How to use this course

John Dalton gave chemistry its atoms. Before him, “atom” was a philosophical word. After him, every element had atoms of a characteristic weight, and chemical formulas became statements about how many of each kind combine. He reached that idea by an unusual road. He was a meteorologist first, and his questions were physical: why do the gases of the air stay mixed, how does water vapour sit in the atmosphere, why does water absorb some gases more than others? This course follows that road from the weather diary to the atomic weight table, and adds the paper on his own colour blindness that made his name a medical term.

Each technical lesson opens with a paragraph for the general reader, then gives the key results in modern form, reconstructs Dalton’s reasoning and his numbers, and ends with exercises whose solutions are folded. Dalton’s weights are on his own scale, hydrogen = 1; modern values use the dalton, one twelfth of the mass of a carbon-12 atom, a unit named after him.

Timeline

Eaglesfield, 1766–1781

John Dalton was born in the hamlet of Eaglesfield, near Cockermouth in Cumberland, in early September 1766. Quakers kept no baptism records, and the date of 6 September was fixed later from family memory. His father Joseph was a handloom weaver with a small holding; his mother, Mary Greenup, came from a local Quaker family. John had an elder brother, Jonathan, who shared his schooling, his work and, as it turned out, his colour vision.

He learned to read and count at the village Quaker school, taught by his father and by John Fletcher. A wealthy Quaker neighbour, Elihu Robinson, noticed him. Robinson kept weather records, made instruments and owned books, and he let the boy use them. Mathematics and meteorology both entered Dalton’s life through Robinson’s house.

At about twelve Dalton tried to run the village school himself. The pupils were barely younger than he was, and the venture soon failed. He worked for a time on the land. In 1781 Jonathan, who was assistant at a Quaker boarding school in Kendal kept by George Bewley, called him to join as a second assistant. He was fifteen.

Kendal and John Gough, 1781–1793

Kendal gave Dalton two things: a library and a teacher. The school had a respectable collection of books on natural philosophy. The teacher was John Gough, a Kendal man blinded by smallpox in infancy, who had taught himself mathematics, botany and natural philosophy and was known throughout the north of England. Gough taught Dalton mathematics, languages and botany, and showed him how to keep systematic scientific records. Dalton later acknowledged him as his guide.

In 1785 Bewley withdrew and the brothers became joint principals. On 24 March 1787 he began a meteorological diary: barometer, thermometer, rain, wind and cloud, noted every day. He kept it for 57 years, and it eventually held more than 200,000 observations.

The diary became his first book. Meteorological Observations and Essays appeared in 1793. Its essays on the trade winds and on the aurora borealis repeated, without his knowing, explanations given earlier by others, including George Hadley’s account of the circulation that bears his name. The book also contained the idea that would lead him to atoms: that water vapour exists in the air as an independent gas, not dissolved in it by chemical attraction.

Manchester and the Lit & Phil, 1793–1800

In 1793 Dalton was appointed tutor in mathematics and natural philosophy at the New College in Manchester, a Dissenting academy founded to educate those excluded from Oxford and Cambridge by the religious tests. Manchester was becoming the first industrial city, rich in cotton mills and in self-made men who wanted science. Its Literary and Philosophical Society, founded in 1781, elected Dalton a member in 1794.

Within weeks he read his first paper there, Extraordinary facts relating to the vision of colours. He described with care what he and his brother saw and did not see, and proposed a cause (Lesson 05). The paper was printed in the society’s Memoirs in 1798. Colour blindness was soon called daltonism in several languages, and the word survives in French as daltonisme.

The teaching load was heavy and left little time for research. In 1800 Dalton resigned and opened a private “mathematical academy”, teaching individual pupils for a modest fee. Private teaching supported him for the rest of his life. The Lit & Phil gave him a room in its house on George Street for teaching and experiments; it remained his laboratory for the rest of his life. In 1800 he became the society’s secretary. The next three years produced almost all the work for which he is remembered.

Weather, vapour and the dew point

For the general reader. Dalton’s chemistry began with the weather. He wanted to know where rain comes from, how water gets into the air and why dew forms. His answer, that water vapour is simply another gas in the air with its own pressure, sounds obvious today. In the 1790s most chemists thought air dissolved water as water dissolves salt.

Vapour as a gas

The prevailing view held that air was a chemical solvent for water. Dalton noticed that the amount of water air can hold depends only on temperature and not on how much air is present: a vacuum above water fills with exactly as much vapour as air does at the same temperature. He concluded that the vapour behaves as a separate gas, coexisting with the air. This is the physical root of his law of partial pressures (Lesson 06).

Dalton gave an early operational definition of the dew point around 1799–1800: pour cold water into a glass, let it warm slowly, and note the temperature at which moisture stops condensing on the outside. That temperature measures the vapour content of the air. He later measured it on the mountains of northern England to study how vapour falls off with height.

A convenient modern fit for \(e_s\) over liquid water (the Magnus form, \(T\) in °C, \(e_s\) in hPa) is

Rain, evaporation and springs

In a paper read in 1799 and printed in 1802, Dalton asked whether the rain and dew falling on England and Wales equal the water carried to the sea by rivers plus the water evaporated. He estimated rainfall at 31 inches a year plus about 5 inches of dew, river outflow at about 13 inches (scaled from the Thames), and evaporation at about 30 inches from soil-filled vessels. The totals disagreed by about 7 inches, which he attributed mainly to errors in evaporation. The paper is one of the first quantitative water budgets of a country, and it argued against the old idea that springs are fed by seawater rising through the earth.

The vision of colours

For the general reader. Dalton realized his vision was unusual when a geranium flower changed colour for him dramatically between daylight and candlelight, while it looked much the same to his friends. He wrote the first careful scientific description of the condition and guessed its cause. His guess was wrong, but he asked for his eyes to be examined after his death to test it, and 150 years later DNA from them settled the question.

Dalton’s account

In his 1794 paper Dalton reported that of the colours most people distinguish in the spectrum, he saw only two or three, essentially yellow and blue, and that red and green were confusable for him. His brother Jonathan saw the same way. He proposed that one of the humours of his eye was tinted blue, absorbing red light. Thomas Young, in his work on colour vision, suggested instead that one of three types of retinal receptor was missing or defective. Dalton did not accept this. He instructed his physician Joseph Ransome to examine his eyes after death. Ransome did so in 1844 and found the vitreous humour perfectly clear. He kept the eyes, and they survive in Manchester.

Three cones, linear algebra

The human retina has three classes of cone with peak sensitivities near 560 nm (L), 530 nm (M) and 420 nm (S). A light with spectral power \(\phi(\lambda)\) produces cone responses

The 1995 diagnosis

In 1995 David Hunt, Kanwaljit Dulai, James Bowmaker and John Mollon extracted DNA from Dalton’s preserved eye tissue. The genes for the L and M photopigments lie side by side on the X chromosome. They found the L-pigment gene but no M-pigment gene: Dalton was a deuteranope, lacking the medium-wavelength cones. The result also matched his own descriptions better than the alternative diagnosis of protanopia that had often been proposed.

Mixed gases and partial pressures

For the general reader. Air is a mixture of a heavy gas (oxygen) and a lighter one (nitrogen). Why do they not separate, like oil and water, with oxygen sinking to the ground? Dalton’s answer was that each gas in a mixture behaves as if the others were not there. From this he obtained the law that the total pressure is the sum of the pressures each gas would exert alone.

Dalton’s model

Dalton followed Newton’s static picture of a gas, from Book II of the Principia, as particles held apart by repulsive forces, which he attributed to atmospheres of caloric, the supposed fluid of heat. His new step, in the 1801 essays, was to assume that particles repel only particles of their own kind. A particle of oxygen then exerts no force on a particle of nitrogen, and each gas forms its own atmosphere, pressing on the walls independently. The “like repels like” assumption was wrong, and the kinetic theory of the 1850s replaced it: in an ideal gas pressure arises from molecular impacts, and molecules of different kinds contribute additively because they do not interact. The law survived its mechanism.

Dalton’s model also implied that each gas in the atmosphere should distribute itself with height as if alone, so the heavier gases should thin out faster. Critics objected that mixtures do not separate. Dalton argued that diffusion was slow but would eventually reach this state. In fact, turbulent mixing keeps the composition of the lower atmosphere uniform up to about 100 km; only above this level does each gas follow its own profile.

Heat, expansion and vapour pressure

For the general reader. In the same series of 1801 essays Dalton measured how gases swell when heated and how the pressure of water vapour climbs with temperature. He found that all gases expand by the same fraction for the same heating. Joseph Louis Gay-Lussac published the same law in 1802 with better data, and his name usually goes on it.

Extrapolating \(V\to0\) gives \(t\approx-273\) °C, the origin of the absolute scale: \(V\propto T\) with \(T=t+273.15\) K. Gay-Lussac credited unpublished experiments of Jacques Charles from the 1780s, which is why the law is also called Charles’s law. Dalton’s independent result was published in the same year; his measurements were less precise.

Vapour pressure by the barometer

Dalton measured the vapour pressure of water by letting a little water rise to the top of a barometer tube, into the Torricellian vacuum, and reading how far the mercury column fell as he warmed the tube in a water jacket. The depression of the column is the vapour pressure. He tabulated it from below freezing to the boiling point, where it equals one atmosphere (30 inches of mercury). He also showed that the same quantity of vapour forms in a space whether or not air is present, supporting Lesson 04.

Dalton, without this equation, guessed that the vapour pressures of different liquids rise by the same amount for the same temperature interval above their boiling points. The guess is roughly right for chemically similar liquids and wrong in general.

Gases dissolved in water

For the general reader. Water absorbs some gases eagerly (carbon dioxide) and others hardly at all (hydrogen). Dalton’s friend William Henry showed in 1803 that the amount dissolved is proportional to the pressure of the gas. Dalton added that in a mixture each gas dissolves according to its own partial pressure, and in trying to explain why different gases dissolve differently, he was led to ask how heavy their particles were.

Henry, a Manchester chemist and manufacturer, published his experiments in the Philosophical Transactions in 1803. Dalton, who had discussed the work with him, extended it to mixtures, which follows from his view that each gas acts independently. In “On the absorption of gases by water and other liquids”, read on 21 October 1803, he argued that absorption is a mechanical effect, not a chemical one, and that the differing solubilities must depend on the size and weight of the gas particles. To pursue that idea he needed the relative weights of the particles. He appended a table of them to the paper, and the atomic theory entered print through a footnote to gas solubility.

Atoms with weights

For the general reader. Philosophers since Democritus had said matter is made of atoms. Dalton made the claim testable. Every element has its own kind of atom, all atoms of one element weigh the same, and compounds form when atoms join in small whole numbers. Then the weights of elements in compounds must come in simple ratios, and one can work backwards to the relative weights of the atoms.

Postulate 1 restates Lavoisier’s conservation of mass and his operational definition of an element. Postulate 3, combined with Joseph Proust’s law of definite proportions (1797), turns composition data into a statement about atoms. Postulate 2 was new and decisive: it gives every element a single number, its atomic weight.

Derivation. Let the compounds be \(\mathrm A_{a_k}\mathrm B_{b_k}\), with atomic weights \(w_A,w_B\). The mass of B per unit mass of A in compound \(k\) is \(\dfrac{b_k w_B}{a_k w_A}\). The ratio for compounds \(k\) and \(l\) is \(\dfrac{b_k a_l}{a_k b_l}\), a ratio of small integers, and the unknown atomic weights cancel. The law therefore tests the theory without requiring any atomic weight to be known.

The rule of greatest simplicity

To get atomic weights from compositions, Dalton needed formulas. Chapter III of the New System gives his rules: if only one compound of two elements is known, presume it binary, one atom of each; if two are known, presume one binary and one ternary (\(\mathrm{AB}_2\) or \(\mathrm A_2\mathrm B\)); and so on. Water became HO and ammonia NH. With the analyses of his day, which put water at about 7 parts oxygen to 1 of hydrogen by weight, his 1808 table set H = 1, O = 7, N = 5, C = 5. His first table of 1803 had O = 5.5, N = 4.2, C = 4.3, using older analyses. The hero illustration shows his symbols and compound weights; every compound weight is the sum of its atoms’ weights.

Combining volumes and the failure of simplicity

For the general reader. Dalton’s theory could not fix its own formulas. In 1808 Gay-Lussac found a clue: gases combine in simple ratios by volume. In 1811 Amedeo Avogadro read the clue correctly, but only by assuming that elements such as oxygen exist as pairs of atoms, which Dalton refused to accept. The confusion lasted half a century.

Dalton’s objection

Dalton had himself considered whether equal volumes contain equal numbers of particles, and rejected it. If they did, then 1 volume of nitrogen with 1 volume of oxygen, containing \(N\) atoms each, could form at most \(N\) compound atoms NO, filling 1 volume, not 2. Producing 2 volumes would require each atom to split, contradicting indivisibility. He also held, from his caloric model, that particles of different gases have different sizes, so equal volumes need not hold equal numbers. In the New System (Part II, 1810) he rejected Gay-Lussac’s results as inexact.

Avogadro’s answer was that the particles of nitrogen and oxygen are themselves double: \(\mathrm N_2+\mathrm O_2\to2\,\mathrm{NO}\). No atom splits; the molecules do. Dalton’s model, in which like particles repel each other, gave no reason for two identical atoms to bind, and Avogadro’s idea was largely ignored until Stanislao Cannizzaro revived it at the Karlsruhe Congress of 1860.

Fame without leaving Manchester, 1803–1830

In the winter of 1803–04 Dalton lectured at the Royal Institution in London. Humphry Davy, its professor of chemistry, was unconvinced; he found the atomic ideas “rather more ingenious than important”. The first full account of the theory in print came from Thomas Thomson of Edinburgh, who visited Dalton in 1804 and included it in the third edition of his System of Chemistry (1807). In 1808 Thomson and William Hyde Wollaston published analyses of oxalates and carbonates that confirmed multiple proportions. Dalton lectured in Edinburgh in 1807, and in 1808 Part I of A New System of Chemical Philosophy appeared, dedicated to the Lit & Phil. Part II followed in 1810 and Volume II, Part I in 1827. The work was never finished.

Dalton disliked the letter symbols introduced by Jöns Jacob Berzelius in 1813, preferring his own circles, and he resisted both Avogadro’s molecules and the improved atomic weights that Berzelius derived from careful analysis. His experimental skill was modest; his instruments were simple and his data often rough. His strength was the bold, simple hypothesis, pursued with stubborn consistency.

He declined to stand for the Royal Society in 1810. He was elected in 1822 without having applied. That year he visited Paris, where he was received at the Académie des sciences, which had elected him a corresponding member in 1816 and made him one of its eight foreign associates in 1830. In 1826 he received one of the first two Royal Medals of the Royal Society. Through all of this he lived as a lodger with the family of the Reverend William Johns, in George Street, taught private pupils and attended the Quaker meeting on Sundays. He never married.

Last years, death and legacy, 1830–1844

Honours accumulated. Dalton took part in the British Association for the Advancement of Science from its foundation in 1831. Oxford gave him a DCL in 1832 and Edinburgh an LLD in 1834. From 1833 the government paid him a pension of £150 a year, doubled in 1836. Among his last private pupils was the young James Prescott Joule, son of a Salford brewer, who went on to establish the mechanical equivalent of heat.

A stroke in 1837 left him partly disabled, and a second in 1838 affected his speech. He continued his weather records. He made his last entry on 26 July 1844, and on the morning of 27 July he was found dead, having fallen from his bed. Manchester gave him a civic funeral; his body lay in state in the Town Hall and more than 40,000 people filed past. He was buried in Ardwick Cemetery. Ransome examined his eyes as he had asked (Lesson 05).

Legacy

• Atomic theory: the idea that each element has atoms of a definite weight became the foundation of chemistry. Corrected by Avogadro’s molecules and Cannizzaro’s method, it led to the periodic table and, by the end of the century, to physical evidence for atoms.
• Gas physics: the law of partial pressures underlies respiratory physiology, diving, anaesthesia, atmospheric science and chemical engineering.
• Meteorology: the 57-year Manchester record, the dew-point method and the concept of water vapour as an independent constituent of air.
• Vision: the first scientific account of colour blindness, and a rare case of a historical diagnosis made by molecular genetics.
• Honours: the unit of atomic mass, the dalton (Da); the Dalton Medal of the Manchester Lit & Phil (from 1898); statues by Francis Chantrey and William Theed in Manchester; the lunar crater Dalton.

Much of his archive was destroyed when the Lit & Phil building was bombed during the Second World War. The surviving manuscripts are in the John Rylands Library.

Connections

People linked to John Dalton across this collection. A name without a link has no page here yet. See John Dalton in the network of all 337 lives →

Teachers and advisors

• John Gough 1781-1793

Students

• James Prescott Joule

Influenced by

• Antoine Lavoisier
• Isaac Newton
• Elihu Robinson

Influenced

• Amedeo Avogadro
• Jöns Jacob Berzelius
• Stanislao Cannizzaro

Colleagues and collaborators

• Humphry Davy
• William Hyde Wollaston 1808
• Thomas Thomson 1804-1808
• William Henry 1803

Rivals

• Count Rumford
• Joseph Louis Gay-Lussac
• Thomas Young

Family

• Jonathan Dalton

Also mentioned in this life

• Henry Cavendish
• Rudolf Clausius

Fields

• chemistry 21 lives
• physics 13 lives
• meteorology 6 lives

Sources and further reading

Biography

1. John Dalton, Wikipedia.
2. A. Thackray, Dalton, John, Complete Dictionary of Scientific Biography, via Encyclopedia.com.
3. Manchester Literary and Philosophical Society, John Dalton, notable past members.
4. W. C. Henry, Memoirs of the Life and Scientific Researches of John Dalton, Cavendish Society, London, 1854.
5. A. Thackray, John Dalton: Critical Assessments of His Life and Science, Harvard University Press, 1972.
6. F. Greenaway, John Dalton and the Atom, Heinemann, 1966.

Science

1. J. Dalton, Meteorological Observations and Essays, London, 1793.
2. J. Dalton, Extraordinary facts relating to the vision of colours, Memoirs of the Literary and Philosophical Society of Manchester 5 (1798) 28–45.
3. J. Dalton, Experimental essays on the constitution of mixed gases; on the force of steam or vapour from water and other liquids; on evaporation; and on the expansion of gases by heat, Memoirs Manchester Lit. Phil. Soc. 5 (1802) 535–602.
4. J. Dalton, On the absorption of gases by water and other liquids, Memoirs Manchester Lit. Phil. Soc., 2nd series, 1 (1805) 271–287.
5. J. Dalton, A New System of Chemical Philosophy, Manchester, 1808–1827. Excerpts and the 1808 table of weights, Classic Chemistry, Le Moyne College.
6. D. M. Hunt, K. S. Dulai, J. K. Bowmaker, J. D. Mollon, The chemistry of John Dalton’s color blindness, Science 267 (1995) 984–988.
7. N. E. Holden, Atomic weights and the international committee: a historical review, Chemistry International 26 (2004).
8. Dalton, John, History of Hydrology wiki.
9. A. J. Rocke, Chemical Atomism in the Nineteenth Century: From Dalton to Cannizzaro, Ohio State University Press, 1984.