Flames. — Ordinarily  when  we  speak  of  a  flame  we
mean  a  gas  which  is  combining  with  oxygen.  The  hy-
drogen flame  is  simply  the  phenomenon  accompanying
the  act  of  combination  of  the  two  gases  hydrogen  and
oxygen.  Owing  to  the  fact  that  we  are  surrounded  by
oxygen,  we  speak  of  hydrogen  as  the  burning  gas.  How
would  it  be  if  we  were  surrounded  by  an  atmosphere  of
hydrogen?  Plainly,  oxygen  would  then  be  a  burning
gas.  If  we  allow  a  jet  of  oxygen  to  escape  into  a  vessel
containing  hydrogen,  a  flame  will  appear  where  the  oxy-
gen escapes  from  the  jet,  if  a  light  is  applied.  This  is
an  experiment  which  requires  special  precautions,  and,
as  the  principle  can  be  illustrated  as  well  by  means  of
illuminating  gas,  this  may  be  used  instead.  Just  as
illuminating  gas  burns  in  an  atmosphere  of  oxygen,  so
oxygen  burns  in  an  atmosphere  of  illuminating  gas.
Kindling  Temperature  of  Gases. — In  studying  the  action
of  oxygen  upon  other  substances,  we  learned  that  it  is


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INORGANIC  CHEMISTRY.
