Dalton, John

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John Dalton (1766-1844): English Chemist, Meteorologist and Teacher.

John Dalton was born on either September 5 or 6 (the precise date of his birth was never recorded), 1766 in the village of Eaglesfield, in the lake district of northern England. His father, Joseph Dalton, was a weaver and his mother Deborah (nee Greenup) made a meager living selling ink and paper. Educational opportunities were few and far between for children in very small, out of the way villages, far from centers of science, art and literature like London, Dublin and Edinburgh, but the Daltons were Quakers, allowing John and his siblings to attend a local Quaker school. At the same time, Dalton also began studying mathematics and collecting meteorological data with the first of several important mentors in his life, Elihu Robinson, a “gentleman of property” in the area.

Dalton began his lifelong career very early, becoming a teacher, possibly at the same Quaker school he had attended, at the tender age of twelve. Not surprisingly, Dalton had some difficulty maintaining his authority with his students, many of whom were his age. One of his pupils later reported that the students frequently challenged Dalton to fights in the graveyard next door to the school and that Dalton punished them by locking them in the school during the dinner hour. It is possible that this experience contributed to his stiffly formal teaching style.

At fifteen, Dalton joined his older brother Jonathan in the nearby town of Kendal to work as an assistant at a boarding school owned by their cousin George Bewley. Bewley retired and sold the Dalton brothers the school, which they ran for the next twelve years. While in Kendal, Dalton met his second important mentor, John Gough. Gough, blind since early childhood, encouraged Dalton’s pursuit of scientific enquiry and helped him develop his habit of empirical investigation into the questions that concerned him. In 1793, on the recommendation of Mr. Gough, Dalton moved to the industrial city of Manchester to become a tutor in mathematics and natural philosophy (science) at the New College there. He brought with him the manuscript of his first book, Meteorological Observations and Essays, dedicated to Mr. Gough. The book, published in 1798, was based on Dalton’s daily meteorological observations, a habit of data collection he maintained until the day before his death. In it, he proposed that, contrary to current scientific opinion, the atmosphere was a mixture of 80% nitrogen and 20% oxygen, rather than being a more complex specific compound of elements. He measured air pressure and its variation with temperature, along with the capacity of air to absorb water vapor. He also proposed that a gas in a mixture of gases acted independently of them, not attracting or repelling the other gases in the mix, but instead acting as if these other gases were simply not present. This independence meant that every gas in the mixture exerted the same amount of pressure that it would have if it had been the only gas present—Dalton’s Law of Partial Pressure. The book was one of the first of its kind, and helped to establish meteorology as a serious scientific discipline, prompting John Frederic Daniell (a contemporary of Dalton’s) to proclaim Dalton as the “Father of Meteorology.” The book also illustrated Dalton’s intensely personal reliance on his own empirical research. He tended to dismiss any data collected by others, writing, “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 that I can attest by my own experience.”

Dalton remained at the College for six years before deciding that becoming a private tutor of mathematics and physics would allow him more time to pursue his personal scientific studies. He continued to conduct experiments and to collect data, and often presented the results of his research to the Manchester Philosophical Society, which he had joined on October 3, 1794. His first paper to the Society, presented on October 31 of the same year, was entitled “Extraordinary Facts Relating to the Vision of Colors,” in which Dalton acknowledged his own color blindness. Both John and Jonathan Dalton suffered from what is now called “color deficiency” (true color blindness or monochromatism is extremely rare) or the inability to perceive some colors in visual stimuli. There are several kinds of color blindness, each caused by a genetic mutation in the gene that codes for a particular type of chemical that allows retinal cells (cones) to respond to different wavelengths of light.

Dalton suffered from red color-deficiency, writing that “All crimsons appear to me to consist chiefly of dark blue: but many of them seem to have a tinge of dark brown. I have seen specimens of crimson, claret and mud, which were very nearly all alike.” Dalton went on to propose that his problems with color vision might be caused by “a colored medium, probably some modification of blue, I suppose it must be the vitreous humor” (a jelly-like substance found inside the eyeball itself),“otherwise I apprehend that it might be discovered by inspection, which has not been done.” In fact, the word denoting color blindness is based on his surname in French (daltonien), Spanish (daltónico), Italian (daltonico) and Portuguese (daltônico). Upon his death, Dalton’s eyes were examined and found to be anatomically normal.

Dalton’s most famous contribution to science was his Atomic Theory. The idea that matter might be composed of particles so small that they were invisible to the naked eye was first elaborated by the Greek philosopher Democritus (460 – 370 B.C.E.), who proposed that all matter was composed of tiny particles called atoms (from the Greek atomos or “uncuttable”). Dalton rejected the idea, then popular, that all atoms in all kinds of matter were alike. Instead he suggested that all atoms of a particular element were identical, but atoms that made up different elements varied in both size and mass. He went on to suggest that more complex compounds were formed by combinations of two or more different atoms, and that chemical reactions consisted of re-arrangements of atoms. He formulated The Law of Multiple Proportions, in which he stated that when atoms combine to form compounds, the ratio of their weights was always a whole number. When a fixed amount of an element was combined with a second element with an unknown mass, the ratios of the masses will also be a small whole number. Dalton supported his theory by experimentation, determining the relative weight of atoms by examining the way that elements like hydrogen (which he assigned an arbitrary weight of 1) combined with fixed amounts of each other. He presented his atomic theory to the Manchester society in 1803 in a series of papers. Encouraged by his peers in the society, he published his results in the two-volume book, New System of Chemical Philosophy (part one in 1808 and part two in 1810). Despite problems with his measurement of atomic weight, his theory was fundamentally sound, and eventually became part of the foundation of modern chemistry.

After 1816, Dalton did very little in the way of important work in science. Instead he lived quietly, spending his time collecting meteorological data and tutoring young children in math and science. In 1826 French chemist Pierre-Joseph Pelletier came to Manchester to talk with the author of atomic theory and was very surprised to find that Dalton was so little known in his home town that he had a great deal of difficulty finding his address. Finally, he discovered Dalton in a small house on a back street helping a young boy with his sums. He asked, “Do I have the honor of addressing M. Dalton?” to which Dalton replied, “Wilt thou sit down while I put this lad right about his arithmetic?” Dalton’s atomic theory earned him election to the Royal Society in London and in Edinburgh, as well as an honorary degree from Oxford University and selection as one of only eight foreign associates to the French Academy of Sciences. He remained in Manchester for the rest of his life, moving from the home of one friend to another, living simply and frugally, until he suffered a stroke and died on July 27, 1844 at the age of 78.

Further Readings:

John Price Milligan, John Dalton, 1906.

Henry Enfield Roscoe, John Dalton and the Rise of Modern Chemistry, 1895.


Barbara Blatchley

Agnes Scott College

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