AN^°mbef,bi89T-}       History  of  Argon  and  Helium.  549 
only  served  to  increase  the  admiration  with  which  this  great  inves- 
tigator is  generally  regarded.  Cavendish,  after  repeatedly  sparking 
this  "phlogisticated  air,"  z.  e.,  nitrogen  with  oxygen,  found  that  some 
always  remained  that  could  not  be  converted  into  nitric  acid,  and 
that  it  constituted  about  part  of  the  whole.  Whether  he  re- 
garded this  gas  as  an  impurity  or  as  nitrogen  cannot  be  determined, 
but  it  is  more  than  likely  that  what  he  had  in  the  top  of  his  inverted 
U  tube  was  what  we  now  call  argon.  Cavendish's  experiments  were 
repeated,  and  it  was  found  that  the  amount  of  his  unsparkable  gas 
was  proportional  to  the  amount  of  air  operated  upon.  A  sufficient 
quantity  was  made  to  determine  its  spectrum,  and  it  was  found  that 
it  did  not  give  the  spectrum  of  nitrogen,  but  of  argon.  Next,  Ray- 
leigh  and  Ramsay  made  argon  in  quantity  from  air  by  removing,  one 
after  the  other,  constituents  of  the  latter  ;  '  thus  moisture  by  means 
of  phosphorus  pentoxide,  oxygen  by  means  of  sparking  with  hydro- 
gen, carbon  dioxide  and  nitrous  acid  by  means  of  caustic  alkalies, 
and,  finally,  nitrogen  by  means  of  red  hot  magnesium  and  magne- 
sium vapor.  This  is  a  very  tedious  operation,  especially  the  remov- 
ing of  the  last  traces  of  nitrogen.  They  then  proved  that  chemical 
nitrogen  does  not  contain  more  than  traces  of  argon,  by  treating  a 
large  quantity  of  the  former  in  the  same  way  as  they  had  treated  the 
air.  They  invariably  found  argon  present,  but  only  to  a  small  frac- 
tion of  the  extent  it  would  have  been  there  if  atmospheric  nitrogen 
had  been  used.  Thus,  where  they  would  have  obtained  30  c.c.  of 
argon  if  atmospheric  nitrogen  had  been  used,  they  actually  only 
found  3-3  c.c.  of  argon.  This  had,  of  course,  been  introduced  from 
the  air  and  the  water  used,  and  to  their  minds  proves  that  chemical 
nitrogen  does  not  contain  argon. 
PROPERTIES  OF  ARGON. 
The  density  of  argon  made  by  the  Cavendish  oxygen  method 
was  found  to  be  1970,  H2,  or  the  hydrogen  molecule,  being  taken 
as  1  ;  while  that  of  argon  made  by  means  of  magnesium  was  found 
to  be  19-90.    The  spectrum  in  wave  lengths  is  : 
Blue  line,  wave  length   487*91  Strong. 
"     "       "       "    476*501  Fairly  strong,  char- 
"      "       "       "    473 '53  f       acteristic  triplet 
"       "    472*56 )        of  lines. 
Red  line,      "       "    696-56  Strong. 
"     "        "       "   •  •  •  705*64 
