.jpg)
John Dalton (6 September 1766-27 July 1844) was an English chemist, physicist and meteorologist.
He introduced the atomic theory into chemistry. He also researched colour blindness; as a result, the umbrella term for red-green congenital colour blindness disorders is Daltonism in several languages.
John Dalton was born on 5 or 6 September 1766 into a Quaker family in Eaglesfield, near Cockermouth, in Cumberland, England. His father was a weaver. He received his early education from his father and from Quaker John Fletcher, who ran a private school in the nearby village of Pardshaw Hall. Dalton's family was too poor to support him for long and he began to earn his living, from the age of ten, in the service of wealthy local Quaker Elihu Robinson.
When he was 15, Dalton joined his older brother Jonathan in running a Quaker school in Kendal, Westmorland, about 72 km from his home. Around the age of 23, Dalton may have considered studying law or medicine, but his relatives did not encourage him, perhaps because being a Dissenter, he was barred from attending English universities. He acquired much scientific knowledge from informal instruction by John Gough, a blind philosopher who was gifted in the sciences and arts.
At 27, he was appointed teacher of mathematics and natural philosophy at the Manchester Academy in Manchester, a dissenting academy (the lineal predecessor, following a number of changes of location, of Harris Manchester College, Oxford). He remained for seven years, until the college's worsening financial situation led to his resignation. Dalton began a new career as a private tutor in the same two subjects.
In 1794, shortly after his arrival in Manchester, Dalton was elected a member of the Manchester Literary and Philosophical Society, the Lit & Phil, and a few weeks later he communicated his first paper on Extraordinary facts relating to the vision of colours, in which he postulated that shortage in colour perception was caused by discoloration of the liquid medium of the eyeball. As both he and his brother were colour blind, he recognised that the condition must be hereditary.
Although Dalton's theory was later disproven, his early research into colour vision deficiency was recognized after his lifetime. Examination of his preserved eyeball in 1995 demonstrated that Dalton had deuteranopia, a type of congenital red-green colour blindness in which the gene for medium wavelength sensitive (green) photopsins is missing.
Arguably the most important of all Dalton's investigations are concerned with the atomic theory in chemistry. While his name is inseparably associated with this theory, the origin of Dalton's atomic theory is not fully understood. The theory may have been suggested to him either by researches on ethylene (olefiant gas) and methane (carburetted hydrogen) or by analysis of nitrous oxide (protoxide of azote) and nitrogen dioxide (deutoxide of azote), both views resting on the authority of Thomas Thomson.
The main points of Dalton's atomic theory, as it eventually developed, are:
-Elements are made of extremely small particles called atoms.
-Atoms of a given element are identical in size, mass and other properties; atoms of different elements differ in size, mass and other properties.
-Atoms cannot be subdivided, created or destroyed.
-Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
-In chemical reactions, atoms are combined, separated or rearranged.
Dalton published his first table of relative atomic weights containing six elements (hydrogen, oxygen, nitrogen, carbon, sulfur and phosphorus), relative to the weight of an atom of hydrogen conventionally taken as 1.
Dalton suffered a minor stroke in 1837, and a second in 1838 left him with a speech impairment, although he remained able to perform experiments. In May 1844 he had another stroke; on 26 July, while his hand was trembling, he recorded his last meteorological observation. On 27 July, in Manchester, Dalton fell from his bed and was found dead by his attendant.
More information: Science History Institute
by those who take an interest in it.
John Dalton
No comments:
Post a Comment