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Terrestrial helium consists almost exclusively (all but ~2ppm) [16] of 4 He. 4 He's boiling point of 4.2 K is the lowest of all known substances except 3 He. When cooled further to 2.17 K, it becomes a unique superfluid with zero viscosity. It solidifies only at pressures above 25 atmospheres, where it melts at 0.95 K.
Helium is a commonly used carrier gas for gas chromatography. The age of rocks and minerals that contain uranium and thorium can be estimated by measuring the level of helium with a process known as helium dating. [28] [30] Helium at low temperatures is used in cryogenics and in certain cryogenic applications.
This glossary of chemistry terms is a list of terms and definitions relevant to chemistry, including chemical laws, diagrams and formulae, laboratory tools, glassware, and equipment. Chemistry is a physical science concerned with the composition, structure, and properties of matter , as well as the changes it undergoes during chemical reactions ...
Cleveite was the first known terrestrial source of helium, which is created over time by alpha decay of the uranium and accumulates trapped (occluded) within the mineral. The first sample of helium was obtained by William Ramsay in 1895 when he treated a sample of the mineral with acid . [ 3 ]
Helium is the smallest and the lightest noble gas and one of the most unreactive elements, so it was commonly considered that helium compounds cannot exist at all, or at least under normal conditions. [1] Helium's first ionization energy of 24.57 eV is the highest of any element. [2]
The idea for the polar wind originated with the desire to solve the paradox of the terrestrial helium budget. This paradox consists of the fact that helium in the Earth's atmosphere seems to be produced (via radioactive decay of uranium and thorium) faster than it is lost by escaping from the upper atmosphere. The realization that some helium ...
An observation of the new yellow line had been made earlier by Janssen at the 18 August 1868 solar eclipse [13], and because their papers reached the French academy on the same day, he and Lockyer usually are awarded joint credit for helium's discovery. Terrestrial helium was found about 27 years later by the Scottish chemist William Ramsay.
This was a foundational discovery that eventually changed the whole of chemistry and physics. He is credited with discovering the element thallium, announced in 1861, with the help of spectroscopy. He was also the first to describe the spectrum of terrestrial helium, in 1865.