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CHEMISTRY

Atomic theory 200th anniversary

October 21, 2003 - 200th anniversary of presentation by British scientist John Dalton of the first table of atomic weights to the Manchester Literary and Philosophical Society. His theory that each element is composed of a unique type of atom, with distinct masses and properties, laid the foundations for modern chemistry.

When John Dalton presented his atomic theory to sceptical colleagues on October 21, 1803, the humble teacher and devout Quaker could not have imagined that he would spark a scientific revolution that is still spurring exciting research two centuries later.

In his address to the Manchester Literary and Philosophical Society, Dalton not only dispelled the airy notions of prevailing alchemists but replaced these with an order and structure for all the chemical data then available, paving the way for chemistry to become a modern science.

In 1802, when he was 36, he began to develop his theory of matter: that all chemical elements are composed of atoms, and that the atoms of each element have a distinct weight. It was not a new idea -- it was initially put forward by the Greek philosopher Democritus -- but Dalton was the first to suggest that atoms were not merely “metaphorical”, and to propose a way to measure them. He didn’t get the weights quite right -- for instance he calculated that an oxygen atom was seven times heavier than a hydrogen atom, while today we know that oxygen weighs 16 times as much as hydrogen, carbon 12 times as much, and so forth. But Dalton clearly saw that when elements combined, they had to do so in fixed proportions.

His research, published in the New System of Chemical Philosophy, provided science with a key means of organising the elements into a “periodic table” to allow accurate predictions for missing elements to be made. Before 1800 only about 30 fundamental elements had been identified. Dalton’s theory resulted in a further 27 elements being discovered over the next 40 years. Today there are currently 111 known elements, with the heaviest 18 -- those weightier than uranium -- only existing in the laboratory.

Born in 1766 in Cumberland, Dalton took up his first teaching post at the age of 12. Later he taught maths and chemistry at the New College in Manchester. After becoming secretary and later president of the Manchester Literary and Philosophical Society, he gave private classes until his death in 1844. But the lifelong teacher never stopped learning.

Indeed, biographers have pointed out that it was Dalton’s refusal to accept at face value untested theories of others that led him to formulate his pioneering thesis. In his own words: “Having been in my progress so often misled by taking for granted the results of others, I have determined to write as little as possible but what I can attest by my own experience.”

As a young man, Dalton began keeping daily records of the weather in the Lake District, and this intense interest in the atmosphere led him to a key breakthrough during an experiment to test the properties of gases needed to make medicinal soda water. Based on his assumption that all elements combined atom-by-atom in whole number ratios, Dalton found he could measure exactly how much gas would dissolve in a given volume of water.

The initial scepticism towards his atomic theory eventually gave way to admiration: one of only a handful of scientists to have a statue erected in his honour during his lifetime, Dalton remains one of northwest England’s most revered sons. More than 40,000 people are said to have filed past the coffin of the quiet Quaker who never married and had few friends.

Though he is best remembered for the atomic theory, Dalton made important discoveries in other areas too, including his theory that colour blindness was hereditary. The condition was one of several obstacles he faced in his search for answers to the big scientific problems of the day. A poor man using crude equipment and often inexact measurements, it was ultimately his leap of imagination that hasled to his being remembered as the father of modern chemistry.

Sources
PUBLISHED: 16/10/2003; STORY: Joanna Griffin
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