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By convention, the part of the total pressure of a mixture that results from one component is called the partial pressure of that component. Dalton's law of partial pressures states that the total pressure of a mixture of gases is the sum of the partial pressures of the various components. Dalton derived the law of partial pressures from his work on the amount of water vapor that could be absorbed by air at different temperatures.
It is therefore fitting that this law is used most often to correct for the amount of water vapor picked up when a gas is collected by displacing water. 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.
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.
In it he elaborated on some of the practical details of his theory: that the atoms within a given element are all exactly the same size and weight, while the atoms of different elements look—and are—different from one other. Dalton eventually composed a table listing the atomic weights of all known elements.
His atomic theories were quickly adopted by the scientific community at large with few objections. Nobel Laureate Professor Sir Harry Kroto, noted for co-discovering spherical carbon fullerenes, identified the revolutionary impact of Dalton's discoveries on the field of chemistry: "The crucial step was to write down elements in terms of their atoms I don't know how they could do chemistry beforehand, it didn't make any sense. From to the day he died, Dalton served as president of the Manchester Literary and Philosophical Society, the organization that first granted him access to a laboratory.
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