John Dalton

In the early 19th century John Dalton, a British schoolteacher and chemist, was fascinated by the patchwork puzzle of chemical elements. His understanding of atoms and how they combined to form different elements led to a revolution in scientific thought and helped create the modern world.

JOHN’S EARLY LIFE

John Dalton was born on September 6, 1766, in the village of Eaglesfield, in Cumberland (now Cumbria). His parents belonged to the fundamentalist Christian movement known as the Quakers and he was educated at the Quaker village school. Young John was so good at his studies that when he was 12 he became a teacher there. In 1781 he became a teaching assistant at the Quaker school in Kendal, and four years later became joint principal with his brother. While there he came under the influence of the wealthy, blind scientist John Gough, who taught him mathematics, meteorology and botany.

In 1793, Dalton was appointed professor of mathematics and natural philosophy at New College, Manchester. This college was established by followers of the Presbyterian Church movement. Before this, only members of the Church of England could attend university. In 1800 he became secretary of the Manchester Literary and Philosophical Society. It was at this time that Dalton became interested in chemistry, and in how the various chemical elements combine with one another to form chemical compounds.

DALTON’S DISCOVERIES

In 1803, Dalton suggested that the tiniest particles of a chemical element are atoms of that element. This had been suspected by many thinkers since the time of the Ancient Greeks, but Dalton was the first to use science to show that it could be true. He realized that atoms of different chemical elements join together in fixed numbers based on their weights to make chemical compounds. This achievement was known as his atomic theory.

At first, some scientists did not agree with his atomic theory, but by the end of the 19th century lots of evidence showed that he was largely right. Dalton also believed that atoms could not be divided up, but we now know that this is not true. There is a whole world of particles, such as electrons, smaller than atoms. This did not matter at the time though. Dalton had shown the world that atoms are the basic building blocks of the objects we see around us and that all our chemistry is about atoms.

FURTHER SCIENTIFIC RESEARCH

Dalton’s later work concentrated on atomic weights. He was the first scientist to understand that chemical elements could be classified according to their atomic weights. He realized the importance of atomic weights after studying how gases dissolved in water. He concluded that their mixing depended on the weight of the individual atoms of the gases. He devised a system of chemical symbols and formulae and drew up a table of the atomic weights of all the elements then known.

His theory of atomic weights contained errors. At first, he had not realized that atoms group together to form molecules. In 1811 this idea was shown by Italian physicist Amedeo Avogadro to be true. But Dalton’s general idea was right, and a precise value could then be given to the mass of each atom.

His studies of the Earth’s atmosphere contributed a great deal to meteorology. He was the first person to confirm that rain is caused by a drop in temperature and not a change in atmospheric pressure, as previously thought. He also studied aurora, the dancing “lights” seen at the north and south poles, as well as the Earth’s magnetism and wind system. His studies of gases led to Dalton’s Law, which states that the total pressure of a mixture of gases equals the sum of each of the pressures of the gases in the mixture. This was a very important law in chemistry.

Dalton also became the first scientist to describe the medical condition known as colour blindness. This is a defect of vision affecting the ability to distinguish between colours. He had the condition (and so did his brother), and the first of his many readings to the Manchester Literary and Philosophical Society in 1794 was devoted to it.

MODEST MAN OF SCIENCE

Dalton’s ideas brought him great fame and changed the study and use of science everywhere. He gave many scientific lectures throughout Britain. In 1817 he became president of the Manchester Literary and Philosophical Society, a post that he held until his death. The French Académie des Sciences elected him as one of their eight foreign associates in 1830. He also helped found the British Association for the Advancement of Science in 1831.

In private he lived a simple and quiet life as a Quaker. He had few friends and never married. He was deeply dedicated to the search for answers to scientific problems.

Following a stroke in 1837, Dalton became an invalid. He died in Manchester on July 27, 1844, and was given a funeral by the city that was attended by 40,000 mourners. Since 1884 there has been a statue to him in the entrance to Manchester Town Hall.