A very heavy, inert gaseous element of the noble gas group, occurring in the atmosphere in the proportion of one volume is about 20 millions. It was discovered by Ramsay
in 1898. It can be condensed to a liquid boiling at -107° C., and to a solid which melts at -111.9° C. Symbol Xe
(formely also X
); atomic number 54; atomic weight 131.3. [Webster 1913 Suppl.