AmMi0rch,S)t.rnK}         Life-History  of  a  Doctrine.  127 
their  backs  on  the  electro-chemical  theory.  In  fact,  the  old  electro- 
chrmical  theories  in  their  original  forms  were  untenable,  but  this  is 
quite  a  different  thing  from  saying  that  electrical  charges  have  noth- 
ing to  do  with  chemical  action.  It  appears  to-day  that  these  elec- 
trical charges  are  the  controlling  factors  in  chemical  phenomena — 
but  of  that  farther  on. 
The  next  change  that  took  place  in  the  conception  of  the  atom 
was  that  which  followed  the  discovery  of  Frankland  that  there  is  a 
limit  to  the  number  of  atoms  that  can  combine  with  any  other  given 
atom.  This  was  followed  up  by  Kekule  and  the  doctrine  of  valence 
was  the  result.  Atoms  differ  from  one  another  in  respect  to  the 
number  of  other  atoms  with  which  they  can  combine.  It  would  be 
interesting  to  follow  the  life-history  of  this  doctrine  of  valence.  It 
has  had  a  most  eventful  career.  It  has  been  chastened  by  experi- 
ence, and  now  it  appears  to  us  freed,  to  a  great  extent,  from  the 
faults  of  youth.  It  is  far  from  dead.  Indeed  it  is  probably  at  the 
beginning  of  its  career.  The  phenomena  of  valence  must  be  reck- 
oned with,  and  the  study  of  these  phenomena  carries  us  back  to  the 
atoms  and  leads  us  to  seek  in  them  the  causes  of  the  differences  in 
the  composition  of  the  compounds  which  are  formed  by  their  union. 
It  has  unquestionably  been  shown  that  the  original  form  of  the 
doctrine  of  valence  is  not  tenable.  Elements  cannot  be  classified 
rigidly  under  a  few  heads  as  univalent,  bivalent,  trivalent,  quad- 
rivalent, etc.,  nor  can  we  hold  the  other  view  that  all  the  elements 
have  either  an  even  number  or  an  odd  number  of  valences  or  bonds, 
though  there  appears  to  be  some  truth  in  this  latter  view.  The 
artiads  and  perissads  of  our  youth  may  return  to  us,  but  before  they 
are  received  it  will  be  necessary  for  us  to  ask  them  a  few  questions, 
and  for  them  to  answer  them  satisfactorily.  In  fact,  we  have  learned 
that  the  phenomena  of  valence  need  to  be  studied  carefully  before 
we  can  discover  the  laws  that  govern  them.  The  views  that  pre- 
vail to-day  are  but  the  foreshadowing  of  a  broader  conception  of 
valence.  This  subject  is  very  much  to  the  front  at  present.  The 
speculations  of  Werner  with  reference  to  complex  inorganic  com- 
pounds have  awakened  wide  interest  and  have  set  many  to  think- 
ing. One  cannot  ignore  the  mass  of  evidence  put  forward  by  Wer- 
ner that  tends  to  show  that  in  many  compounds  it  is  necessary  to 
assume  the  existence  of  a  core  or  inner  sphere  consisting  of  a  group 
of  atoms  in  combination,  this  core  holding  in  combination  a  definite 
