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Chemist John Dalton is credited with pioneering modern atomic theory. He was also the first to study color blindness.
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In 1803 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 1800s, 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 1803, 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 1808. 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. In so doing, he became the first scientist to explain the behavior of atoms in terms of the measurement of weight. He also uncovered the fact that atoms couldn't be created or destroyed.
Dalton's theory additionally examined the compositions of compounds, explaining that the tiny particles (atoms) in a compound were compound atoms. Twenty years later, chemist Amedeo Avogadro would further detail the difference between atoms and compound atoms.
In A New System of Chemical Philosophy, Dalton also wrote about his experiments proving that atoms consistently combine in simple ratios. What that meant was that the molecules of an element are always made up of the same proportions, with the exception of water molecules.
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