John Dalton

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John Dalton about 1834

John Dalton (born September 6, 1766 in Eaglesfield , Cumberland , † July 27, 1844 in Manchester ) was an English naturalist and teacher . Because of his fundamental investigations into atomic theory, he is considered one of the pioneers of chemistry . In his honor, the atomic mass unit u (outdated: amu) has been named "Dalton" in the Anglo-American region .

Live and act

John Dalton, drawing around 1879

Dalton grew up as the son of a Quaker weaver and attended a school where he himself worked as a teacher. He was probably only twelve years old at the time. From 1781 he ran a school in Kendal with his brother and cousin.

Dalton initially dealt - like his former teacher Elihu Robinson - primarily with meteorology . At the age of 21 he carried out meteorological studies himself and manufactured scientific devices such as barometers and thermometers for himself and other customers. Since 1787 he has given public lectures on mechanics, optics, astronomy and geography.

In 1791 he published the work Meteorological Observations and Essays . 1793 Dalton got a job at the "Warrington Academy" in Manchester as a teacher of mathematics and science. The salary in this higher education institution was significantly better than in the school in Kendal. It was not until 1796 that Dalton began to deal with chemistry, especially with the composition of the air.

However, around 1800 he gave up the apprenticeship and contented himself with income from private tuition. From 1800 Dalton came into contact with the Literary and Philosophical Society of Manchester. This company enabled him to print his meteorological work and set up his own laboratory.

Dalton dealt with air, water, wind and rain. First he developed the theory that in a gas mixture each individual gas has its own partial pressure at each temperature, independent of the other gases ( Dalton's law ).

Dalton also hypothesized that the vapor pressures are the same for all liquids at the same temperature from the boiling point. He found a constant expansion of the amount of gas above the liquid for every degree of temperature increase - for water and diethyl ether . However, this is not the rule with other liquids.

In this context, Dalton (independent of Joseph Louis Gay-Lussac , after whom the law is usually named) found the law of the proportional gas expansion of pure gases (oxygen and nitrogen) with an increase in temperature (1801). Here he found the proportionality factor 1/266 ≈ 0.00375, just like Gay-Lussac (the correct value is around 0.365). Because of this relationship, the gas volume of gases decreases at low temperatures. Dalton coined the term “ absolute zero ” for a gas, i.e. the temperature at which a gas should be liquid or solid.

In the following year Dalton investigated the composition of the air and came to quite precise results with regard to the oxygen (21%) and nitrogen (79%) content.

Dalton then also dealt with gas mixtures over a dissolving liquid. His friend William Henry had shown that the solubility of a single gas is proportional to the pressure of the single gas above the liquid ( Henry's law ). Now Dalton assumed that gas particles with different weight properties also show changes in their solubility behavior. The light particles (e.g. hydrogen) of a gas mixture are less well dissolved in a solvent at the same pressure than the heavy particles (e.g. carbon dioxide particles). Due to the solubility of gases at the same pressures and based on analytical measurements by other authors, Dalton was able to draw up a table with the relative atomic weights of particles. On October 21, 1803, he submitted a note to the Literary and Philosophical Society of Manchester .

He set the relative weight for hydrogen equal to 1. For carbon it came in 1803 to 4.3, for carbon monoxide to 9.8, for oxygen to 5.5, for nitrogen to 4.2, for water to 6.5. for ethyl alcohol to 15.1. How he came up with these values, he did not explain. Later he improved the indication of the atomic weights; in 1810 it came to 5.4 for carbon, 7 for oxygen, 6 for nitrogen. For Dalton, water, ethanol and carbon monoxide were still the smallest (atomic), indivisible particles. Dalton could not yet distinguish between molecule and atom. The values ​​of Dalton were still far from the correct values, and he also gave partially incorrect sum formulas (as for nitric acid). According to Wilhelm Ostwald , one reason was that he refused foreign work and especially non-English work. The atomic weights were determined much more precisely from 1810 by Jöns Jakob Berzelius .

From studies by Alexander von Humboldt and Gay-Lussac it was known that water had 12.6 parts by weight of hydrogen and 87.4 parts by weight of oxygen. Dalton now assumed that substances can only pair in very specific weight ratios (synthesis). For example, an element A can combine with element B to form a connection AB. It can also be possible that 2 parts A with 1 part B form the connection A 2 B, three parts A could also combine with one part B to form A 3 B. In any case, an integral multiple of a component must always occur during the pairing. This hypothesis later became the law of multiple proportions . The atom hypothesis, which had previously only been postulated speculatively, was thus scientifically proven. In his work on atomic theory, he processed the findings of Jeremias Benjamin Richter .

This hypothesis was soon supported by Thomas Thomson and William Hyde Wollaston . In 1808 they determined that carbonate contained one part of carbon dioxide and bicarbonate contained two parts of carbon dioxide. Thomson was also able to support the law of multiple proportions with the help of the salts of oxalic acid . The law of multiple proportions, however, only got its meaning through the atomic relationships related to molecules and ions. According to Dalton, compounds with a stoichiometric structure were later referred to as daltonides .

The thought of the atom and the atomic weights came up as a by-product of his list. Thomas Thomson took Dalton's ideas and disseminated them through a textbook, which also received a lot of attention abroad.

Only Jöns Jakob Berzelius determined the relative weights of connections more precisely in 1810.

The exact distinction between atom and molecule was only made many years later by Stanislao Cannizzaro , because chemists had no idea at the time that two identical atoms (e.g. hydrogen atoms) could combine to form a hydrogen molecule.

In London, Dalton gave many lectures in front of the “Royal Institution”. In 1816, Dalton was elected a corresponding member of the Académie des Sciences in Paris.

In 1822 he was offered membership in the Royal Society . In 1826 he was the first scientist to receive the Royal Medal (also known as the "Gold Medal") for his services in the field of chemistry. In 1834 he was elected to the American Academy of Arts and Sciences and in 1835 as an honorary member ( Honorary Fellow ) in the Royal Society of Edinburgh . Since 1820 he was a foreign member of the Bavarian Academy of Sciences and since 1827 a corresponding member of the Prussian Academy of Sciences .

The lunar crater Dalton and the asteroid (12292) Dalton are named after him.

Summary of the important work of John Dalton

  • Research on thermal expansion of gases and determination of the thermal expansion coefficient .
  • 1805: Formulation of the law of partial pressures, Dalton's law , according to which the total pressure of a gas mixture is equal to the sum of the pressures of the individual gases.
  • Development of vapor tension tables from investigations into the processes of boiling, evaporation , evaporation .
  • As early as 1787, meteorological observations made him suspect that rain is caused by a drop in temperature in the atmosphere. He contradicted the prevailing opinion that pressure differences in the upper atmosphere are responsible for precipitation.
  • Discovery of the law of multiple proportions (1808): "If two elements form several compounds with one another, the mass ratios with which the elements appear in these compounds are in relation to one another in the ratio of small whole numbers."
  • Establishment of a table of atomic weights. These were a template for the later establishment of the periodic table of the elements .
  • Development of the first chemical sign language for atoms and molecules, which however did not catch on because Jöns Berzelius' sign language was more popular.
  • Dalton also discovered the red-green poor eyesight (Daltonism) from which he suffered. He told one of his friends to dissect one of his eyes after his death, as he suspected the strange colors he saw to be a blue liquid in his eye.
  • Occupation with linguistics

To atomic theory

His most important publication is likely to be his book A New System of Chemical Philosophy, printed in 1808 . In it he presented his atomic hypothesis, which defines the atom as the smallest unit of matter. In it he hypothesized that there are as many different atoms as there are elements: "Elements consist of the same and indivisible particles that are characteristic of the respective element, the atoms". Dalton established (and that was the most striking difference to the Democritus atomic model ) that the atoms differ in their mass. According to Dalton, atoms can be combined with one another (= synthesis) or combined atoms can be separated from one another (= analysis).

Through his considerations, the law of constant proportions ( Joseph-Louis Proust , 1794), his law of multiple proportions and the law of equivalent proportions (Richter, 1791) could be explained. The unit of atomic mass was therefore also called Dalton earlier. One dalton (Da) roughly corresponds to the mass of a hydrogen atom (1.66 · 10 −27 kg) and is also referred to as the atomic mass unit u .

John Dalton established the first scientifically based atomic model, which can be summarized in four key statements:

  1. Every substance consists of the smallest, indivisible spherical particles, the atoms.
  2. All atoms of a given element have the same volume and mass. The atoms of different elements differ in their volume and mass.
  3. Atoms are indestructible. They can neither be destroyed nor created by chemical reactions.
  4. In chemical reactions, the atoms of the starting materials are only rearranged and connected to one another in certain proportions.


  • A New System of Chemical Philosophy , Volume 1, Part 1, Manchester, London 1808, Archives , Volume 1, Part 2, 1810, Archives , Volume 2, Part 1, 1827, Archives
  • Meteorological observations and essays , Manchester, 2nd edition 1834, Archives
  • Wilhelm Ostwald (Ed.): Fundamentals of the atomic theory. Treatises by J. Dalton, WH Wollaston , Leipzig, Ostwalds Klassiker 1889, Archives , therein by Dalton: On the absorption of the types of gas by water and other liquids (Memoirs Lit. Phil. Soc. Manchester, Volume 1, 1805), A new system of chemical philosophy, 1808, part 1, chapter 2, pp. 141-144


Web links

Commons : John Dalton  - collection of images, videos and audio files

Individual evidence

  1. ^ Karl Heinrich Wiederkehr in Fritz Krafft (ed.): Great natural scientists. Biographical Lexicon. Düsseldorf 2nd edition. 1986, pp. 95f.
  2. a b c d e f Wilhelm Ostwald: Dalton. In: Günther Bugge (ed.): The book of the great chemists. Verlag Chemie, Weinheim 1974, ISBN 3-527-25021-2 , pp. 378-386
  3. ^ Bugge, The Book of Great Chemists, Verlag Chemie 1979, Volume 1, p. 382
  4. ^ Günther Bugge: The book of the great chemists . Verlag Chemie, Weinheim 1974, ISBN 3-527-25021-2 , p. 390, footnote 14
  5. Note: The solubility of gases in a liquid also depends on other factors such as dissociation, but this was not known at the time
  6. ^ FW Clarke : The Atomic Theory . In: Science . tape 18 , no. 460 , October 23, 1903, p. 513-529 , doi : 10.1126 / science.18.460.513 , JSTOR : 1630501 (English).
  7. ^ John Dalton: On the Absorption of Gases by Water and Other Liquids . In: Memoirs of the Literary and Philosophical Society of Manchester, Second Series . tape 1 , 1805, pp. 271-87 (English, [accessed April 24, 2019]). (English)
  8. Bugge, The Great Chemists, Volume 1, p. 383
  9. ^ A b William H. Brock: Viewegs Geschichte der Chemie. Vieweg & Sohn Verlagsgesellschaft, 1992, ISBN 3-528-06645-8 , pp. 84 ff.
  10. ^ Fellows Directory. Biographical Index: Former RSE Fellows 1783–2002. Royal Society of Edinburgh, accessed October 19, 2019 .
  11. ^ Member entry of John Dalton at the Bavarian Academy of Sciences , accessed on January 22, 2017.
  12. ^ Members of the previous academies. John Dalton. Berlin-Brandenburg Academy of Sciences and Humanities , accessed on March 11, 2015 .