Argon
Argon is an element that belongs to the noble gas family. It has an atomic number of 18 and is known by the atomic symbol Ar. It has a freezing point of -308.7°F (-189.3°C), a boiling point of -302.6°F (-185.9°C) and an atomic weight of 39.948.
Argon might have been discovered more than a hundred years earlier if a scientific instrument, the spectroscope, had been invented sooner. The story of argon's discovery began in the 1780s, when Henry Cavendish tried repeatedly to combine oxygen with nitrogen, but always had a small bubble of gas left over. Although Cavendish speculated that this was some kind of nonreactive gas, he lacked the technology with which to analyze it. As it turned out, this bubble would contain five gases comprising a new class of elements that scientists had never before imagined.
The thread was picked up again in the late 1800s when John William Strutt ( Lord Rayleigh) noticed that nitrogen extracted from the air was always slightly heavier than nitrogen obtained from chemical compounds. After ruling out various explanations, Rayleigh published his puzzling question in a scientific journal, and Sir William Ramsay called his attention to Cavendish's observations. The two chemists spent the summer of 1894 trying to solve the mystery.
By August Ramsay had isolated an inert, or nonreactive, gas by passing atmospheric nitrogen over hot magnesium until no more nitrogen was absorbed. He asked Sir William Crookes to analyze the leftover gas with a recently invented instrument called the spectroscope, which splits the light given off by an element into its different colors, revealing a characteristic set of spectral lines. Sure enough, the mystery gas 's spectrum was unique, meaning it was a new element. Together, Ramsay and Rayleigh named the gas argon, after the Greek word for " lazy" (argos), because it would not react with other elements to form compounds. Over the next few years, Ramsay and other scientists succeeded in discovering the rest of argon's inert gas family ( helium, neon, krypton, xenon, and radon).
Since then, scientists have learned much more about argon. It is the most plentiful of the inert gases, which are also called noble or rare gases. In fact, argon is not rare; it makes up nearly 1% of the Earth's atmosphere. Also, trace amounts occur in minerals and meteorites, and the gas is released during radioactive decay of a potassium isotope. Argon is relatively easy to liquefy and solidify. Very pure argon can be produced in commercial quantities by separating it from liquefied air. In its natural gaseous state, argon is colorless, tasteless, and odorless and does not form any stable compounds. It has five radioactive isotopes that are produced by nuclear reactions but do not occur naturally.
Argon has played an important role in the development of modern electric lighting. In the early 1900s American Irving Langmuir (1881-1957), a new employee at General Electric's research laboratory, was looking for a way to extend the life of GE 's incandescent light bulb, which was manufactured by creating a vacuum within the bulb to preserve the filament. Langmuir discovered that the filament would last much longer if the bulb was filled with a nonreactive gas. This improvement revolutionized the early lighting industry and saved customers millions of dollars in electricity costs. Although nitrogen was used as the filler gas at first, argon--which is even less reactive--replaced it.
Today, argon is used in many other kinds of electric lights. Along with a little mercury vapor, argon and argon-krypton mixtures are used to fill fluorescent lights. In addition to supplementing the light given off by mercury vapor radiation, argon makes the lamps easier to start and helps regulate their voltage. Argon has also made neon advertising signs more colorful. When argon gas is added to neon in the tubing, the lamp glows with a blue or green color, in addition to the bright red given off by neon alone.
Since World War II, argon has also become one of the most important industrial gases. The greatest amounts of argon are used in metal welding and cutting. The gas serves as a blanket or shield that allows the metal to cool in time to prevent oxidation by the atmosphere. Argon is also used in metallurgical processing, its fastest growing application. For example, in aluminum refining, the use of argon results in a purer product and less environmental pollution than does its alternative, chlorine. Production of stainless steel and silicon also uses argon, and the gas is employed in radiation detectors, such as Geiger counters and ionization chambers as well as in various types of electron tubes and gas lasers.
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