Amjuneri9Pi3arm'}      What  the  Atmosphere  is  Made  of.  261 
were  tried  and  even  the  volcanic  gases  of  Iceland,  to  which  country 
Sir  William  journeyed  on  his  quest.  Meteorites  were  heated  and 
a  great  range  of  such  experiments  tried,  but  all  without  avail. 
"  And  all  this  time,"  said  the  lecturer,  "  it  was  ail  about  us  in  the 
commonest  thing  we  had,  the  air."  This  was  in  1896  and  the  means 
which  were  to  put  the  great  results  into  the  hands  of  the  investi- 
gators were  just  coming  into  reach  of  scientific  men.  This  was 
liquid  air,  and  by  way  of  return  for  courtesies  of  the  laboratory 
the  first  litre  of  this  product  made  by  an  Englishman  in  a  new  way 
was  sent  to  Sir  William.  The  relation  of  this  to  the  discovery  was 
that  cocoanut  charcoal  has  an  extraordinary  appetite  for  gas  and 
the  colder  it  becomes  the  more  gas  it  will  absorb.  Charcoal  chilled 
to  the  very  low  figure  of  the  temperature  of  liquid  air  does  select 
from  mixtures  of  gases  in  contact  with  it  all  of  those  then  known 
to  be  in  the  air  excepting  helium.  This  gas  was  not  absorbed  in 
such  processes  and  the  scientists  collected  it  in  sufficient  quantity 
for  the  determination  of  its  various  chemical  constants. 
Gaps  in  the  rhythmic  order  of  qualities  as  shown  by  the  tabula- 
tions of  chemical  elements  furnisned  the  suggestion  that  there 
were  missing  elements  and  the  low  temperatures  of  liquid  air  and 
hydrogen  furnished  a  means  of  separating  them  from  their  com- 
panions. In  a  rough  way  the  process  may  be  explained  by  the 
different  temperatures  at  which  the  different  gases  liquefy  or 
freeze.  One  gas  will  become  liquid  while  another  is  still  a- gas,  or 
freeze  while  its  companion  is  a  liquid.  The  gas  can  be  pumped  out 
or  the  liquid  drawn  off,  while  the  second  gas  remains  in  different 
condition. 
The  litre  of  liquid  air  that  was  received  by  Sir  William  was  used 
largely  for  amusement,  the  scientists  literally  playing  with  the 
strange,  new  material.  When  it  was  nearly  all  gone,  scientific  tests 
were  suggested  and  the  familiar  treatments  were  given  it.  It  was 
found  that  the  residue  had  a  higher  weight  than  the  normal  one 
for  argon.  From  this  circumstance  there  came  the  separation  of 
krypton,  so  called  because  it  had  been  hidden. 
Of  course  with  the  increasing  ease  with  which  liquid  air  could 
be  obtained  such  experiments  were  repeated  and  it  was  noticed 
that  even  with  the  krypton  taken  out,  there  was  always  a  bubble 
of  residue.  This  was  tested  in  the  ways  known  to  chemists ;  the 
spectrum  showed  that  it  was  still  a  different  gas  and  xenon,  the 
stranger,  was  produced.    It  was  the  separation  of  the  gases  by 
