I think this first appeared in the puzzle newsletter The Ag Mine — 12 chemical elements can be spelled using element symbols:

ArSeNiC
AsTaTiNe
BiSmUTh
CArBON
CoPPEr
IrON
KrYPtON
NeON
PHOsPHORuS
SiLiCoN
TiN
XeNoN

See Transmutation.