n. Symbol He
A colorless, odorless inert gaseous element occurring in natural gas and with radioactive ores. It is used as a component of artificial atmospheres and laser media, as a refrigerant, as a lifting gas for balloons, and as a superfluid in cryogenic research. Atomic number 2; atomic weight 4.0026; boiling point -268.9°C; density at 0°C 0.1785 gram per liter. See Periodic Table.
[From Greek hēlios, sun (so called because its existence was deduced from the solar spectrum); see sāwel- in the Appendix of Indo-European roots.]
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