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John Dalton

versatile scientist

John Dalton was born at Eaglesfield, near Cockermouth in Cumberland, England, on September 6, 1766, the son of a devout Quaker family. He was such a brilliant youth that he became a teacher when barely 12 years old.

John Dalton

Work on Meteorology

Influenced by a friend of his family, an amateur weather observer, Dalton became deeply interested in meteorology. In 1787 he began a daily journal of weather observations that he painstakingly maintained for over 40 years. In 1793 he published a definitive work called Meteorological Observations and Essays.

In 1793, Dalton became a teacher of mathematics and natural philosophy at Manchester Academy. He remained in that position until the academy was relocated to York, in 1803, upon which time he became a public and private teacher of mathematics and chemistry.

Work on Color Blindness

In 1794, Dalton was elected a member of the Manchester Literary and Philosophical Society. A few weeks after his election he communicated his first paper on Extraordinary Facts Relating to the Vision of Colours, in which he postulated that shortage in color perception was caused by discoloration of the liquid medium of the eyeball. What makes this paper so remarkable is that a shortage of color perception -- "color blindness" -- had not even been formally described or even officially noticed by the scientific community until Dalton wrote about his own visual problem. Although Dalton's theory lost credence in his own lifetime, the thorough, methodical nature of his research was so broadly recognized that "Daltonism" is still a common term for color blindness.

Work on Gases

Dalton became a secretary of the Manchester Literary and Philosophical Society in 1800. In 1801 he presented a series of papers entitled Experimental Essays on the constitution of mixed gases; on the pressure of steam and other vapors at different temperatures, both in a vacuum and in air; on evaporation; and on the thermal expansion of gases. In these essays he concluded, among other things, that the variation of vapor pressure for all liquids is equivalent, for the same variation of temperature, reckoning from vapor of any given pressure.

Work on the Atomic Theory

Dalton published his atomic theory in 1808 in a book called A New System of Chemical Philosophy. His theory was based on three important propositions: that all matter is composed of extremely small, indivisible, and indestructible particles called atoms; that the atoms of one element are all exactly alike in every respect including weight but are different from the atoms of every other element; and that when elements combine to form compounds their atoms combine in simple numerical proportions such as one to one, two to one, and four to three. The ideas of atoms had been suggested centuries earlier by the Greek philosopher Democritus, so the concept was not entirely unfamiliar to Dalton's contemporaries. But Dalton's complete formulation of a consistent theory was a breakthrough. One of the most important features of the theory was its proposal that atoms differed from each other by weight. This was something measurable, making Dalton's the first quantitative atomic theory ever advanced. Chemists had long puzzled over why a substance such as copper carbonate, however prepared, always contained the same proportions by weight of copper (five parts), oxygen (four parts), and carbon (one part). Dalton's theory that elements combine atom by atom in simple numerical proportions explained it, because if all atoms of a particular element have the same weight, they must have definite combining weights.

Dalton tried to work out the relative weights of different atoms from the proportions by weight of the elements in certain compounds, so becoming the first to prepare a table of atomic weights. He also drew up a system of notations to represent elements, discarding the obscure drawings that had been handed down from the alchemists of ancient times. He created clear sysmbols to stand for the atoms of different elements, and used them in drawings that showed what took place during chemical reactions. For example, molecules were shown as groups of atom symbols linked together.

Dalton's symbols of atoms of different elements together with their atomic weights
Dalton's symbols of atoms of different elements together with their atomic weights

Dalton's design for alum
Dalton's design for alum

Later Work

Dalton was president of the Manchester Literary and Philosophical Society from 1817 until his death, contributing 116 papers. One paper, read in 1814, explains the principles of volumetric analysis, in which he was one of the earliest workers. In 1840 a paper on the phosphates and arsenates was refused by the Royal Society, so he published it himself. He did the same with four other papers, two of which -- On the Quantity of Acids, Bases and Salts in Different Varieties of Salts and On a New and Easy Method of Analyzing Sugar -- contain his discovery that certain anhydrates, when dissolved in water, cause no increase in its volume.

John Dalton died on July 27, 1844.

Awards and Honors

As a devout Quaker, Dalton shunned public acclaim, even refusing to be nominated for membership of the Royal Society. In 1822 his determined admirers elected him to the society without his knowledge, and in 1832 he was persuaded to accept a Doctorate of Science from the University of Oxford. Dalton had a problem in wearing his Oxford gown, however, because it was scarlet and Quakers wore no red. Because he could not bring himself to disappoint his friends, Dalton fell back on his color blindness and remarked that the University gown appeared gray to him.

In 1833 the British government conferred on him a pension of 150, which was raised to 300 in 1836.

All but two of the statements in Dalton's Atomic Theory are still considered valid today. The statement "Atoms cannot be subdivided, created, or destroyed into smaller particles when they are combined, separated, or rearranged in chemical reactions" is inconsistent with the existence of nuclear fusion and fission. The statement "All atoms of a given element are identical in their physical and chemical properties" is also not precisely true, as the different isotopes of an element have varying numbers of neutrons in their nuclei, though the number of protons remains consistent.

SOURCE
Anthony Feldman and Peter Ford Scientists and Inventors, The People Who Made Technology from Earliest Times to Present Day New York: Facts on File, 1979

SEE ALSO
Democritus

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This page was last updated on 04/21/2017.