John Dalton

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John Dalton (1766-1844), an English scientist, one of the founders of modern chemistry — through his quantitative formulation of an atomic theory — and a pioneer founder of modern meteorology, taught mathematics and physical sciences at New College, Manchester, having begun his teaching career at the age of 12 years as founder and teacher of an elementary school.  Dalton inferred from experimental studies of the atmosphere, and other researches on gases, liquids and solids, an atomic theory of matter, the ancient Greeks having first suggested idea, Robert Boyle and Issac Newton having accepted it without evidence, Dalton providing its experimental support, establishing that all elements did not have the same mass and size, a finding that not only contributed to the development of his atomic theory but also led to the proof of the law of definite proportions, hinted at but little understood by chemists before Dalton.

He developed a table of weights of the atoms of different elements, a law of partial pressures (Dalton's law) — "....where the pressure exerted by each gas in a mixture [of gases] is independent of the pressure exerted by the other gases, and where the total pressure is the sum of the pressures of each gas." — and a law about the combining of elements called the law of multiple proportions, which only makes sense in the light of Dalton's atomic theory.

Dalton suffered from color-blindness and studied that affliction, which later physicians referred to as Daltonism.

In the vestibule of the Manchester Town Hall are placed two life-sized marble statues facing each other. One of these is that of John Dalton, by Chantrey; the other that of James Prescott Joule, by Gilbert. Thus honour is done to Manchester's two greatest sons - to Dalton, the founder of modern Chemistry and of the Atomic Theory, and the discoverer of the laws of chemical-combining proportions; to Joule, the founder of modern Physics and the discoverer of the law of the Conservation of Energy. The one gave to the world the final and satisfactory proof of the great principle, long surmised and often dwelt upon, that in every kind of chemical change no loss of matter occurs; the other proved that in all the varied modes of physical change no loss of energy takes place. Dalton, by determining the relative weights of the atoms which take part in chemical change, proved that every such change - whether from visible to invisible, from solid to liquid, or from liquid to gas - can be represented quantitatively by a chemical equation; and he created the Atomic Theory of Chemistry by which these changes are explained. Joule, by exact experiment, proved the truth of the same statement for the different forms of energy. —Sir Henry Roscoe, John Dalton and the Rise of Modern Chemistry. 1895.

Dalton's law of multiple proportions

Dalton's law of multiple proportions: If two elements can form more than one compound, the weights of an element in different compounds present in ratios of integral (whole) numbers. For instance, consider the elements nitrogen, N, and oxygen O. The element oxygen occurs in the compounds NO and NO₂. The ratio of oxygen weights (1:2) in these compounds contains the integral numbers 1 and 2. (Note that in modern chemistry the concept "number of atoms" replaces "weight", used by Dalton. Now we say that the ratio of numbers of O-atoms in different NO_x compounds is a rational number, a number expressible as an integer (whole number) or a ratio of integers.

By extension of Dalton's law of multiple proportions, the subscripts m, n, k, ... in a compound A_mB_nC_k⋅⋅⋅ are integral numbers. In other words, the law applies to the ratio of the differing elements in a given compound as well as the ratio of the same element in differing compounds.

The law of multiple proportions led Dalton to take the mass of the lightest element, hydrogen, as the unit of atomic mass, and upholds the validity of matter's nature as comprising atoms of different masses.

Early life

John Dalton entered the world in a thatch-roofed cottage in the village of Eaglesfield in England's northwest coastal county of Cumberland, on September 6 or 7, 1766, of Quaker parents Joseph and Deborah, his father a hand-loom weaver. He early showed intellectual promise and perseverance in learning. He had competent and inspirational schoolmasters, including an instrument-maker and meteorologist, Elihu Robinson, who gave him much attention. According to English chemist, H.E. Roscoe, who first isolated the element, vanadium, Dalton wrote of his early years in a letter dated 1832:

The writer of this was born at Eaglesfield, near Cockermouth, Cumberland. Attended the village schools there, and in the neighbourhood, till eleven years of age, at which period he had gone through a course of mensuration, surveying, navigation, etc.

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