Helium

Helium

I just read with interest on 25^th August an article in THE DECCAN HERALD by Shri C Sivaram of the Indian Institute of Astrophysics, Bengaluru. It is about the gas Helium. It is stated that Helium is the second lightest element after hydrogen, or twice as heavy as hydrogen. Hydrogen gas constitutes three-fourths or 75% of the chemical composition of the universe and Helium is the second most abundant chemical element after hydrogen constituting 24% of the chemical composition of the universe. All other elements make up the remaining 1% to 2% of the chemical composition of the universe. He says that it is surprising that although humans were aware of and indeed making use of several chemical elements like iron, copper, gold, silver, etc early in history, the discovery of helium happened only 150 years ago and that of hydrogen by Henry Cavendish about 100 years earlier, in 1766.

Helium was discovered in the gaseous atmosphere surrounding the Sun by the French astronomer Pierre Janssen, who detected a bright yellow line in the spectrum of the solar chromosphere during an eclipse in 1868; this line was initially assumed to represent the element sodium. That same year the English astronomer Joseph Norman Lockyer observed a yellow line in the solar spectrum that did not correspond to the known D1 and D2 lines of sodium, and so he named it the D3 line. Lockyer concluded that the D3 line was caused by an element in the Sun that was unknown on Earth; he and the chemist Edward Frankland used the Greek word for sun, hēlios, in naming the element. The British chemist Sir William Ramsay discovered the existence of helium on Earth in 1895. Ramsay obtained a sample of the uranium-bearing mineral cleveite, and, upon investigating the gas produced by heating the sample, he found that a unique bright yellow line in its spectrum matched that of the D3 line observed in the spectrum of the Sun; the new element of helium was thus conclusively identified. In 1903 Ramsay and Frederick Soddy further determined that helium is a product of the spontaneous disintegration of radioactive substances.

Shri Sivaram says that “very recently, in May 2018, helium was detected for the first time in the atmosphere of an exoplanet. This is WASP 107b who’s atmosphere is being stripped by it’s host star. The planet’s atmosphere is sweltering hot at 500 degrees Celsius and extends to over a 1,000 km. This has enabled an excited state of helium to be identified. The planet has the size of Jupiter but is bloated up so that its average density is much less than water”. 

Commenting about its usage, he says “Helium on earth has been put to several uses. It liquefies at four degrees Kelvin and is used in cryogenics to cool complex systems to very low temperatures. Helium becomes a superfluid at two degrees Kelvin. The Large Hadron Collider uses large amounts of liquid helium in its vacuum chambers and huge superconductor magnets. Helium is also used in balloons.

Hydrogen was earlier used in airships, even to cross the Atlantic, like in the Zeppelins, 80 years ago. But the explosion of the Hindenburg in 1938 at the end of its voyage put an end to this mode of air travel. Helium being inert is not flammable and is currently used in airships to transport freight. It is also used in diving equipment, industrial processes like welding and, of course, in large-scale cooling. It is feared that the supply of helium may run out in the next few decades, although new sources are being discovered”.