Iridium

3 definitions found

From The Collaborative International Dictionary of English v.0.48 [gcide]:

  iridium \i*rid"i*um\ ([-i]*r[i^]d"[i^]*[u^]m), n. [NL., fr. L.
     iris, iridis, the rainbow. So called from the iridescence of
     some of its solutions. See {Iris}.] (Chem.)
     A rare metallic element of atomic number 77, of the same
     group as platinum, which it much resembles, being
     silver-white and indifferent to most corrosive agents, but


     harder, more brittle, and with a higher melting temperature
     (2410[deg] C, versus platinum 1772[deg] C). With the
     exception of osmium, it is the heaviest substance known, its
     specific gravity being 22.4. Symbol Ir. Atomic weight 192.22.
     [1913 Webster +PJC]
  
     Note: Iridium usually occurs as a native alloy with osmium
           (iridosmine or osmiridium), which may occur alone or
           with platinum. Iridium, as an alloy with platinum, is
           used in bushing the vents of heavy ordnance. It is also
           used for the points of gold pens, and in a finely
           powdered condition (iridium black), for painting
           porcelain black.
           [1913 Webster]

From WordNet (r) 2.0 [wn]:

  iridium
       n : a heavy brittle metallic element of the platinum group; used
           in alloys; occurs in natural alloys with platinum or
           osmium [syn: {Ir}, {atomic number 77}]

From Elements database 20001107 [elements]:

  iridium
  Symbol: Ir
  Atomic number: 77
  Atomic weight: 192.217
  Very hard and brittle, silvery metallic transition element. It has a
  yellowish cast to it. Salts of iridium are highly colored. It is the
  most corrosion resistant metal known, not attacked by any acid, but is
  attacked by molten salts. There are two natural isotopes of iridium, and
  4 radioisotopes, the most stable being Ir-192 with a half-life of 73.83
  days. Ir-192 decays into {platinum}, while the other radioisotopes decay
  into {osmium}. Iridium is used in high temperature apparatus, electrical
  contacts, and as a hardening agent for platinum. Discovered in 1803 by
  Smithson Tennant in England. The name comes from the Greek word iris, which
  means rainbow. Iridium metal is generally non-toxic due to its relative
  unreactivity, but iridium compounds should be considered highly toxic.