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Dalton's atoms

The first page of John Dalton's A New System of Chemical Philosophy, published in 1808.

 

Another valuable contribution that John Dalton made to chemistry

John Dalton was the first chemist to have the idea to represent elements, molecules and compounds visually. The current convention is the CPK colouring code (the initials are those of its creators, chemists Robert Corey and Linus Pauling, and Walter Koltun).

The image below compares Dalton's original symbols compared to the modern interpretations.

Compounds comparison

 

 

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John Dalton (1766 - 1844)

John Dalton was born into a Quaker family in Eaglesfield, near Carlisle in Cumbria in 1766. His father's trade was in weaving and his grandfather had been a cobbler. Dalton was the youngest of the three surviving children. The beginning of Dalton's formal education was at the village school, John Fletcher's Quaker Grammar school. In order to financially support his education, Dalton taught at the school when he was only 12 years old! When the school got into financial difficulty and closed, Dalton turned his hand to farm labouring for a short while, as well as working for a well-off Quaker named Elihu Robinson. Elihu Robinson became a mentor to the young John Dalton and encouraged his interest in meteorology.

When Dalton was fifteen years old he moved to Kendall to work as an assistant master in a Quaker boarding school. At some point, when the headmaster gave up his post, the school was bought by Dalton's brother, Jonathan. Dalton remained in Kendall for 12 years, teaching natural philosophy and continuing his own studies and research. As a Quaker, regardless of status in society, the local Meeting House would introduce a member to another Quaker house by certification. Dalton would have been introduced to the Kendall Quaker society early on and been given access to the private libraries of the well-off members. When the Kendall school eventually fell on hard times and closed down in 1793, Dalton moved to Manchester as a mathematics and natural philosophy teacher at New College.

It may seem odd that Dalton was offered a professorship at New College, Manchester, even though he had no academic qualifications and he had not attended university. Quakers, as non-conformists, were not allowed entry into English universities (although they were welcome into higher education in Scotland). The Quakers set up their own schools and teaching networks that, in conjunction with the communication between the Meeting Houses, helped fill teaching posts and introduced new-comers to like-minded researchers. In fact, New College was a Dissenting Academy and had been established by a Unitarian (another group of non-conformists) named Thomas Bond. Another Unitarian (and an ex-Quaker) was a blind scholar named John Gough who became a second mentor to John Dalton. Gough was well-versed in the Classics and also taught mathematics, French and natural philosophy. When New College folded, seven years after his arrival, Dalton remained in Manchester and became a private tutor.

 

Dalton

John Dalton by Charles Turner

When Dalton first arrived in Manchester in 1793 the city had a growing population of around fifty thousand. Dalton felt intimidated by the crowds and the big buildings. Many of these new constructions were mills since the industrial revolution was just beginning and workers were flooding into the cities to find work in the factories. In 1794 Dalton joined the Manchester Literary and Philosophical Society and his first paper, Extraordinary facts relating to the vision of colours was published in the same year. Colourblindness, a condition that both Dalton and his brother were afflicted by, is now known as Daltonism.

Dalton had been interested in meteorology from a young age. He made many excursions to the Lake District to record meteorological effects that included the height of the hills, as well as temperature, pressure and humidity. He even studied the Aurora Borealis and used a theodolite to try to measure the angles and height of this spectacular effect. Dalton took weather measurements three times per day, from 1787 to the end of his life. His paper entitled Meteorological Observations and Essays that was published by the Literary and Philosophical Society in 1793 helped launch meteorology as a serious science. Dalton's interest in meteorology led directly his experimental work on the composition of the air. His 1801 paper, Experimental Essays introduced the idea that air was not a single, 'fluid' substance but a mixture of different gases. He went on to propose that each of the gases in the air exerts a pressure and that air pressure is equal to the total of the pressure of each of these gases. This is now referred to as Dalton's Law of Partial Pressures.

He came to the conclusion, against the popular theory at that time, that atoms of different elements vary in size and mass. He presented his paper A New System of Chemical Philosophy to the Manchester Literary and Philosophical Society in 1803. The concept of atoms was not new. Ancient Greek philosophers, notably Democritus and Leucippus in the 5th Century BC, had introduced the notion of elementary particles. Dalton took the atomic theory a few steps further; not only by proposing that the atoms of different elements vary in size and mass but also that atoms combine in simple proportions. He also introduced the notion that atoms could not be created or destroyed (making nonsense of the alchemists' transmutation claims). However, not all of Dalton's propositions were valid. He referred to molecules as 'atoms' and described the water 'atom' as one atom of hydrogen combined with one atom of oxygen. Although Dalton's Atomic Weights theory did not have a basis in experimentation and observation, his ideas helped other scientists of the day to explain the results of their observations.

Dalton's paper on Atomic Weights was read by his contemporaries in Britain and on the Continent. In his later years he lectured in London and in Paris. It was Humphry Davy who invited Dalton to lecture at the Royal Institution in London but the two scientists did not hit it off. Dalton famously said that Davy 'failed as a philosopher because he did not smoke'. As for Davy, pipe smoking was one of the reasons he disliked Dalton, as well as what Davy described as Dalton's gruff manners and strong, northern accent. However, Dalton's work influenced many scientific researchers of his day. They did not all agree with his Atomic Weights theory but that did not stop them applying the gas laws!

John Dalton never married and he lived in one room that he rented in a building that stood directly opposite that of the Literary and Philosophical Society where Dalton spent the majority of his time. Dalton was appointed as secretary, then Vice President and, for many years, President of the society that held weekly meetings. The Society provided Dalton with work space and Dalton produced between two and four papers each year, either presenting on his own research or commenting on the publications of other scientists. Dalton was a man of habit and routine - he enjoyed playing bowls and walking, smoking his rather large pipe and taking his weather measurements three times every day. Even on the day he died, following two strokes and reportedly with 'a shaking hand', he faithfully recorded his measurements.

Dalton was made a member of the French Académie des Sciences in 1816 and a Fellow of the Royal Society in 1826. He suffered a third, fatal stroke in May 1844. Thousands lined up to file past his coffin in a mark of respect. He is buried in Ardwick Cemetery in Manchester. A lunar impact crater bears his name.

 

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