While he received little formal education, his sharp mind and natural sense of curiosity compensated for a lack of early schooling. At the age of just 12 he joined his older brother in running a local Quaker school, where he remained as a teacher for over a decade. Dalton had two influential mentors during this time: Elihu Robinson, a rich intellectual with an interest in mathematics and science; and John Gough, a blind classics scholar and natural and experimental philosopher. Both these men inspired in Dalton an avid interest in meteorology that lasted for the rest of his life.
In , Dalton published his first scientific paper: 'Meteorological Observations and Essays'. He was keen to pursue further atmospheric and weather research at an academic institution, but as a Quaker was barred from most British universities at the time, so his mentor Gough pulled a few strings and got him a place as a tutor at Manchester College. By the time he arrived in Manchester, Dalton had begun to realise that he saw the world differently from most other people, as he wrote in a letter to Elihu Robinson:.
The Society gave him a room for teaching and research at its premises on George Street. Through this, he gained access to a well-equipped research laboratory, where his scientific output flourished. Though sometimes criticised for the quality of his experiments, Dalton was an enthusiastic investigator who worked late most evenings. He read over papers to the Society, and became its Secretary, Vice-President and, ultimately, President. Through his experimentation, Dalton not only formulated a new atomic theory to explain chemical reactions, upon which much of modern chemistry and physics is based, but he also developed a theory to explain colour vision deficiency, from which he himself suffered.
He was also a figurehead in the world of meteorology. Dalton was interested in the composition of the atmosphere and, by extension, in how components mix together to form gases. He formulated the Law of Partial Pressures in , according to which the pressure of a mixed gas is the sum of the pressures that each of its components would exert if occupying the same space.
He also developed the law of the thermal expansion of gases. Henry Roscoe, a later Manchester chemist, suggested that Dalton was trying to explain why the constituents of a gaseous mixture remain homogeneously mixed instead of separating into layers according to their density, the understanding of which is particularly important in atmospheric studies.
At the end of an paper on the absorption of gases by liquids, Dalton rather casually set out the first table of atomic weights.
Encouraged by the favourable reception this paper received, he developed his theory further, in lectures to the Royal Society in —04 and later in his New System of Chemical Philosophy:. Every particle of water is like every other particle of water; every particle of hydrogen is like every other particle of hydrogen Chemical analysis and synthesis go no farther than to the separation of particles one from another, and to their reunion. No new creation or destruction of matter is within the reach of chemical agency.
Dalton's theory was based on the concept that each element consists of its own unique brand of indivisible atom; atoms of one element are all alike but they differ from atoms of other elements.
Importantly, Dalton assigned atomic weights to the atoms of the 20 elements he knew of at the time. This was a revolutionary concept for the day, which would contribute to the development of the periodic table of the elements later in the 19th century. The below images are reproductions of drawings of atomic formulae by John Dalton, copied from original lent to the Science Museum Group by Manchester Literary and Philosophical Society.
This concept, that atoms of different elements are distinguished by differences in their weights, opened up new fields of experimentation. Each aspect of Dalton's theory has since been amended or refined, but its overall picture remains as the basis of modern chemistry and physics.
Through his work, Dalton also pioneered the use of ball-and-stick models to illustrate the three-dimensional structure of molecules, which are often used in teaching to this day. There he joined the Manchester Literary and Philosophical Society, which provided him with a stimulating intellectual environment and laboratory facilities.
The first paper he delivered before the society was on color blindness, which afflicted him and is sometimes still called Daltonism. Dalton arrived at his view of atomism by way of meteorology, in which he was seriously interested for a long period: he kept daily weather records from until his death, his first book was Meteorological Observations , and he read a series of papers on meteorological topics before the Literary and Philosophical Society between and Arnold Thackray describes how John Dalton's book on meteorology led to his discovery of the nature of atoms.
Since the condition had affected both him and his brother since birth, Dalton theorized that it must be hereditary. He proved his theory to be true when genetic analysis of his own eye tissue revealed that he was missing the photoreceptor for perceiving the color green. As a result of his contributions to the understanding of red-green color blindness, the condition is still often referred to as "Daltonism.
Dalton's interest in atmospheric pressures eventually led him to a closer examination of gases. While studying the nature and chemical makeup of air in the early s, Dalton learned that it was not a chemical solvent, as other scientists had believed.
Instead, it was a mechanical system composed of small individual particles that used pressure applied by each gas independently. Dalton's experiments on gases led to his discovery that the total pressure of a mixture of gases amounted to the sum of the partial pressures that each individual gas exerted while occupying the same space.
In this scientific principle officially came to be known as Dalton's Law of Partial Pressures. Dalton's Law primarily applies to ideal gases rather than real gases, due to the elasticity and low particle volume of molecules in ideal gases. Chemist Humphry Davy was skeptical about Dalton's Law until Dalton explained that the repelling forces previously believed to create pressure only acted between atoms of the same sort and that the atoms within a mixture varied in weight and complexity.
The principle of Dalton's Law can be demonstrated using a simple experiment involving a glass bottle and large bowl of water. When the bottle is submerged under water, the water it contains is displaced, but the bottle isn't empty; it's filled with the invisible gas hydrogen instead.
The amount of pressure exerted by the hydrogen can be identified using a chart that lists the pressure of water vapors at different temperatures, also thanks to Dalton's discoveries. This knowledge has many useful practical applications today. For instance, scuba divers use Dalton's principles to gauge how pressure levels at different depths of the ocean will affect the air and nitrogen in their tanks.
During the early s, Dalton also postulated a law of thermal expansion that illustrated the heating and cooling reaction of gases to expansion and compression. He garnered international fame for his additional study using a crudely fashioned dew point hygrometer to determine how temperature impacts the level of atmospheric water vapor.
Dalton's fascination with gases gradually led him to formally assert that every form of matter whether solid, liquid or gas was also made up of small individual particles. He referred to the Greek philosopher Democritus of Abdera's more abstract theory of matter, which had centuries ago fallen out of fashion, and borrowed the term "atomos" or "atoms" to label the particles.
In an article he wrote for the Manchester Literary and Philosophical Society in , Dalton created the first chart of atomic weights. Seeking to expand on his theory, he readdressed the subject of atomic weight in his book A New System of Chemical Philosophy , published in In A New System of Chemical Philosophy , Dalton introduced his belief that atoms of different elements could be universally distinguished based on their varying atomic weights.
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