JOHN DALTON 1766 - 1844

(G3a, G3b, G3c, G4, W4, Va)

Acknowledgements

Dalton: by the English engraver Charles Turner (1774-1857), 1834 – Prints and Photographs Division, Library of Congress, Washington. Diagram (Atomic Theory): from imgbucket.com/pages/d/dalton’s-atomic-theory. Berzelius: date and artist unknown – Royal Swedish Academy of Sciences, Stockholm. Young: mezzotint by the English engraver Charles Turner (1774-1857), 1830, after a portrait by the English painter Sir Thomas Lawrence (1769-1830) – National Portrait Gallery, London. Diagram (Theory of Colour): licensed under Creative Commons – https://wikileaks.org. Diagram (Theory of Light): licensed under Creative Commons – chemwiki.usdavis.edu.

xxxxxThe English physicist and chemist John Dalton was self-taught, and learnt a great deal of his knowledge from his own observations, and from experiments carried out with home-made apparatus. Despite his lack of advanced equipment, many of his findings proved remarkably accurate. His results were based mainly on the observations and measurements of local atmospheric conditions that he carried out and logged for close on 60 years - a staggering 200,000 or more in number. This huge quantity of data enabled him to make a close study of the nature of gases. He came to the conclusion that a gas could be regarded as a dispersed solid made up of countless tiny particles. Following closer investigation, this led to the formulation of his chemical atomic theory, first put forward in lectures he gave in 1803. By this time, the idea that matter was made up of atoms had become quite widely accepted, but Dalton greatly extended this concept. He advanced the theory that these atoms were of differing weights and combined together in definite proportions. Thus chemical reaction was the rearrangement of atoms from one form of combination to another. Such was the very foundation of atomic chemistry and modern physics.

xxxxxIn 1808 Dalton published his atomic theory in his New System of Chemical Philosophy, and listed the first tentative calculations of the atomic weights of all the elements known at that time. As all these weights were relative, and a standard was therefore required, he used a scale based on the atomic weight of hydrogen as one. Some of his findings were by no means accurate, but the procedure was sound, and proved the first attempt at compiling today’s periodic table of the elements. It was now possible to establish order by arranging elements in accordance with their atomic weights and their reactions. This was a major achievement.

xxxxxDalton’s investigation into the physical properties of air and other gases - the means by which he arrived at his atomic theory - also spawned earlier discoveries. Having noted that when two components combined to form another gas their proportions by weight always remained constant, he experimented further and, in a paper produced in 1803, came up with his law of multiple proportions. Then two years later his treatise Absorption of Gases contained his law of partial pressure. Known still as “Dalton’s Law”, this stated that the pressure exerted by a gaseous mixture is equal to the sum of the partial pressures of its components. And he was the first to publish the notion that all gases which begin with the same temperature expand equally when submitted to higher temperatures.

xxxxxLikewise, his long and close study of weather conditions also resulted in a number of advances in meteorology, contained in his Meteorological Observations and Essays of 1793. Following a study of evaporation and humidity, for example, he produced a table of vapour pressures of water at various temperatures, and he was the first to substantiate that rain was caused by a fall in temperature, and was not due to a change in atmospheric pressure, as many had believed. And after close observation over a long period, he came to the conclusion that the aurora borealis must have some connection with the Earth’s magnetism.

xxxxxDalton was born in Eaglesfield, near Cockermouth in Cumberland, the son of a weaver. He attended a Quaker school in the town, and began teaching there at the age of 12. After ten years or more in Kendal, running a school with his elder brother, he settled in Manchester in 1793 and remained there, working as a teacher and lecturer in mathematics and chemistry. Though he had no formal training in chemical research, he carried out his investigations with immense dedication and application, and, being professionally independent, seldom accepted data that he himself had not “proven”. He was a quiet, unassuming man, and he made few friends. Such was the esteem in which he was held, however, that he was invited to run courses at the Royal Institution in London in the early 1800s, was made a fellow of the Royal Society in 1822, and awarded the society’s gold medal four years later. In 1830 he became an associate member of the French Academy of Sciences. Today he is generally regarded as the founder of modern atomic theory.

xxxxxIncidentally, the idea of matter being made up of atoms goes back well over 2,000 years. The Greek philosophers Leucippus and Democritus of the 5th century BC, and Epicurus of the 3rd century BC all came up with the idea of “atomism”. Democritus (illustrated), who taught at Abdera in Thrace, held that matter was not continuous but made up of invisible “pieces”. Only atoms and empty space existed, everything else was “superficial appearance”. ……

xxxxx…… Dalton was one of the first scientists, if not the first, to give a description of colour blindness. This was contained in a paper he delivered to the Manchester Literary and Philosophical Society, and published in 1794 under the title Extraordinary Facts Relating to the Vision of Colours. He himself suffered from this impairment of vision (as did his brother). His explanation as to the cause of this condition was way off the mark, but nevertheless colour blindness is often known as “Daltonism”.

xxxxxThe Swedish chemist Jöns Berzelius (1779-1848) advanced the work begun by Dalton. He established a table of atomic weights for some 50 elements - achieving a remarkable degree of accuracy - and in 1818 published the relative atomic and molecular masses of no less than 2,000 compounds. He introduced oxygen as a reference standard for atomic masses (replacing Dalton’s hydrogen standard) and his system of chemical symbols and formulae, devised in 1813, remains in use today. His symbols to denote the elements simply took the first letter or letters of the Latin or English name. Thus Fe was for iron (from the Latin word ferrum) and Ca was for calcium. And his research also included experiments on the electrolysis of various solutions, a branch in which his contemporary, the English scientist Humphry Davy, was making progress at the time.

xxxxxBerzelius was born near Linkoping in Ostergotland, and studied science and medicine at Uppsala University. In 1807 he was appointed professor of medicine, botany and pharmacy at the College of Medicine, Stockholm, and from 1815 to 1832 was professor of chemistry at the Royal Caroline Medico-Chirurgical Institute in Stockholm. It was while carrying out research at the Institute that he proved beyond doubt Dalton’s atomic theory and, by his precise methods and new techniques, laid the foundation of modern chemical analysis. His publications included his Textbook of Chemistry in 1803 - a work which went through five editions -, a series of valuable updates on developments in chemistry and physics, and a vast number of papers in the Transactions of the Stockholm Academy. One of the outstanding chemists of his time, he was made a baron in 1835 by Charles XIV of Sweden and Norway.

xxxxxDuring his career, he isolated and identified a number of new elements, including selenium in 1817, silicon in 1823, and thorium five years later. Otherxchemists at this time who contributed in this way were the German Martin Klaproth (1743-1817) (uranium, zirconium and cerium), the Frenchman Louis Vauquelin (1763-1829) (chromium and beryllium), and the Englishman William Hyde Wollaston (1766-1828) (palladium and rhodium).

xxxxxIncidentally, the terms “protein” and “catalyst” were coined by Berzelius, and he was one of the first scientists of this period to group together elements of similar chemical properties. For example, he introduced the collective term “halogens” (salt formers) to describe chlorine, bromine and iodine - elements found as salts in sea water. And after introducing a system with which to classify minerals based on their chemistry, he introduced the group known as silicates. ……

xxxxx…… ThexWollaston Medal, the highest award of the Geological Society of London, was funded with a bequest by the English chemist William Hyde Wollaston, and was first awarded in 1831. It was originally made of palladium, one of the metals he discovered, but it is now made in gold. The first recipient was the English geologist William Smith.

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xxxxxLike Dalton, the English physicist and physician Thomas Young (1773-1829) also showed an interest in the workings of the human eye (the physiology of vision). As a young doctor working in London at this time, he discovered that the lens of the eye, composed as it was of muscle fibres, changed shape to focus on objects viewed at varying distances. At the same time, 1801, he determined that astigmatism (short-sightedness) was due to an irregular curvature of the cornea. Later he also made substantial advances in studying the problems associated with colour perception. He was the first to suggest that the eye only had need of three “receptors” in the retina, one for each of the colours blue, green and red. Developed further by the German physicist Hermann von Helmholtz, this theory of colour mixing became known as the Young-Helmholtz trichromatic theory.

xxxxxIn 1802 Young also began a study of light, and by demonstrating the phenomenon of optical interference established the wave nature of light. Later, in 1817, this led to his explanation of polarisation, based on the proposition that light waves vibrate at right angles to the direction of travel (i.e. they are “transverse”), and not along the line of travel (“longitudinal), as previously assumed. Among other research projects, he spent time on measuring the size of molecules and on studying elasticity, a branch of physics in which an absolute measurement is named “Young’s modulus” in his honour.

xxxxxHe was born in Milverton, Somerset, and studied at the universities of London, Edinburgh, and Göttingen. Apart from producing works on physics and medicine, he also wrote on Egyptology, and, beginning in 1814, made some headway in deciphering the hieroglyphics on the Rosetta Stone. It was the French linguist and historian Jean François Champollion, however, who eventually succeeded in producing a full translation in 1822 (G4).

xxxxxIncidentally, Young’s wave theory of light, valid though it was, was not convincingly explained or proven, and, being in opposition to Newton’s theory, failed to gain general acceptance. It was left to the French physicists Augustin-Jean Fresnel and François Arago to refine and prove this theory. Fresnel presented it to the French Academy in 1815 and then, making practical use of his newly found knowledge, designed greatly improved lenses for use in lighthouses and for stage lighting in the theatre.