An\ulus['  £>hi!rm*}    Romance  of  Chemical  Elements.  575 
important  step  of  increasing  the  groups  was  taken  by  Newlands  in 
his  law  of  "  octaves,"  grouping  eight  elements  together.  Then  in 
1869  came  Mendeleeff  and  independently  Lothar  Meyer  and  an- 
nounced their  periodic  system.  It  is  often  said,  in  textbooks  and 
otherwise,  that  the  periodic  system  was  "discovered."  But  this  is 
misleading,  as  something  that  gradually  develops  with  the  increas- 
ing knowledge  of  mankind  is  not  "suddenly  discovered,"  but  is 
"gradually  attained."  But  Mendeleeff  discovered  something,  and 
that  was  the  prediction  of  two  new  elements.  He  thought,  pre- 
suming the  system  was  correct  and  assuming  there  is  a  unity  and 
persistency  in  the  material  world,  that  some  elements  were  missing, 
and  he  calculated  from  their  assumed  position  the  properties  they 
should  have  and  called  them,  in  1869,  eka-boron  and  eka-silicon. 
Six  years  later  gallium  was  discovered  by  Lecoq  de  Boisbaudran 
and  its  properties  proved  to  be  those  of  eka-boron.  In  1886, 
Clemens  Winkler  found  a  new  constituent  in  argyrodite  of  Frei- 
berg and  termed  it  germanium,  and  its  properties  were  identical 
with  those  predicted  by  Mendeleeff,  as  eka-silicon.  These  predic- 
tions could  only  be  made  because  the  elements  were  near  those  ele- 
ments of  lower  atomic  weights,  and  rilled  out  the  table  practically 
complete.  To-day  we  are  enabled  to  fix  the  end  point  of  the  ele- 
mental series,  viz.,  the  radioactive  elements,  and  thus  limit  the  sys- 
tem to  92  elements. 
Noble  Gases. 
Throughout  the  modern  development  of  chemistry  it  has  been 
believed  that  we  know  exactly  the  constitution  of  air  and  its  per- 
centage of  different  gases :  oxygen,  nitrogen,  carbon  dioxide,  water 
vapor,  etc.  The  announcement  of  Sir  William  Ramsay  and  Lord 
Rayleigh  in  1894  that  they  had  discovered  a  new  gas  in  the  atmos- 
phere, was  therefore  generally  accepted  as  very  doubtful.  But 
there  came  more,  for  not  only  argon,  but  in  1898  neon,  krypton, 
xenon,  and  later  helium,  were  found  to  be  constituents  of  air.  The 
percentage  is  very  small,  and  the  methods  employed  for  determining 
it  are  a  triumph  of  physics.  These  new  gases  developed  to  be  ele- 
ments, although  it  was  at  first  proposed  by  some  chemists  that  argon 
might  be  only  a  different  form  of  nitrogen,  just  like  ozone  is  oxygen 
gas  containing  three  atoms  in  the  molecule.  They  were  elements, 
but  no  compound  could  be  made;  all  means  to  produce  a  chemical 
reaction  with  these  elements  failed.    In  fact  the  name  argon,  from 
