An inert gaseous element of the argon (
noble gas) group, of atomic number 36, occurring in air to the extent of about one volume in a million. It was discovered by
Ramsay and
Travers in 1898. Boiling point, -152.3° C.; melting point, -156.6° C.; symbol,
Kr; atomic weight, 83.8. [
Webster 1913 Suppl.]