World of Scientific Discovery on Johannes Diderik van der Waals
Born into a poor family in Holland, van der Waals was the son of a carpenter. As a young adult, he began teaching elementary school to support himself while training for secondary-level teaching. While working as a headmaster, or school principal, he enrolled at Leiden University, where he studied physics. In 1873, van der Waals completed his doctoral thesis, which was recognized immediately for its insight into behavior of gases. Although little was known at the time about the structure of molecules, van der Waals's dissertation accurately described the molecular forces that dictate gas behavior.
In his essay van der Waals successfully explained, in fairly simple mathematical terms, why gases begin to act unpredictably at extreme temperatures and pressures. Earlier, scientists had learned that a few simple rules govern gas behavior under most conditions. These so-called gas laws, developed by Robert Boyle in the late 1600s and Joseph Louis Gay-Lussac in the early 1800s, describe the relationship between the volume of a gas, its temperature, and its pressure. Although these fundamental laws apply to most gases under normal conditions, they were still fairly crude predictors of gas behavior, and some gases, such as hydrogen and helium, did not always comply with these laws. During the late 1800s, the kinetic theory of gases was developed by James Clerk Maxwell and, independently, by Ludwig Boltzmann, an Austrian physicist. This theory attempted to explain gas behavior at the molecular level, but it assumed that there were no attractive forces between gas molecules, and that the molecular size of gases was so small that their impact on molecular attraction was inconsequential.
Van der Waals recognized that these assumptions were inaccurate. After years of careful work, he introduced a more complicated equation for explaining gas behavior. His equation involved two new constants, or numbers, that had to be determined experimentally for each gas, and that took into consideration molecular structure and attraction. Soon van der Waals was able to simplify his own equation and eliminate the extra numbers needed in the calculations. He did this by using the temperature, pressure, and volume of a gas at its "critical" point--the point where an element's gaseous and liquid states become indistinguishable.
With this new equation van der Waals was able to validate the work of other scientists. For example, when van der Waals was doing his research, scientists knew if gases were allowed to expand, they would eventually cool and pass into a liquid state. This process, known as the Joule-Thomson effect, was a major breakthrough for scientists, but it did not hold true for all gases, particularly hydrogen and helium. Van der Waals's work argued that the liquefaction of hydrogen and helium requires a substantial drop in temperature and a change in pressure. These theories were later verified by Dutch physicist Heike Kamerlingh Onnes, who demonstrated that liquid helium could only be obtained by cooling helium gas to temperatures approaching absolute zero.
Van der Waals's pioneering research opened the door to the modern science of cryogenics, which is the study of materials at very low temperatures. His predictions about gas behavior have enabled nineteenth- and twentieth-century engineers to develop low-temperature processes that are used in surgery, pollution control, radiation detection, and energy supply technologies. For example, without liquid hydrogen fuel as a propellant, our spaceships would not be powerful enough to escape the Earth's atmosphere. Van der Waals's name has also been used to describe the attractive forces between molecules; these are now called van der Waals's forces.
In 1878 van der Waals became professor of physics at the University of Amsterdam, where he remained for nearly thirty years. When he retired in 1907, his son took his place. In 1910 van der Waals was awarded the Nobel Prize in physics in recognition of his work on gas equations and laws.
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