130 
Life-History  of  a  Doctrine. 
/  Am.  Jour.  Pharm. 
I      March,  1903. 
entering  into  combination  with  another  ion,  or  other  ions,  or  by 
being  set  free,  it  becomes  an  atom.  But  more  than  this :  The  elec- 
trical charge  of  an  ion  is  either  a  unit  charge  or  a  multiple  of  this. 
The  bivalent  ion  has  two  charges,  the  trivalent  ion  has  three,  etc. 
The  experimental  basis  for  these  ideas  is  found  in  the  electrolytic 
phenomena  that  are  included  in  the  scope  of  Faraday's  law.  Fara- 
day found  that  a  definite  quantity  ot  electricity  causes  a  definite 
amount  of  decomposition  in  a  conductor  of  the  second  class ;  and, 
further,  he  found  that  when  the  same  current  is  passed  through 
solutions  of  the  salts  of  different  metals  in  series,  the  masses  of  the 
different  metals  that  separate  are  proportional  to  the  combining 
weights  or  the  equivalents  of  these  metals.  To  make  clear  the  full 
significance  of  these  facts  would  require  more  time  than  is  at  my 
disposal.  SufTice  it  to  say,  that  in  terms  of  our  present  theory  it 
takes  twice  as  much  electricity  to  set  a  bivalent  atom  free  as  to  set 
a  univalent  atom  free;  three  times  as  much  for  a  trivalent  atom, etc. 
How  to  conceive  of  one,  two,  three  or  four  charges  of  electricity  on 
an  ion  I  leave  to  the  physicists  to  explain,  though  it  must  be  said 
that  they  are  not  in  the  least  called  upon  to  explain. 
The  atom  has  thus  been  followed  in  its  career  down  to  to-day. 
The  changes  in  our  conceptions  have  been  traced  sufficiently  for  our 
purpose.  It  is  at  present  a  bundle  of  attributes  and  with  these 
attributes  it  is  a  convenient  nucleus  for  thought.  Nothing  has  been 
said  of  the  dynamics  of  the  atom,  by  which  I  do  not,  of  course,  mean 
chemical  dynamics  in  general.  So  far  as  the  atom  is  concerned  our 
knowledge  of  its  motions  may  perhaps  fairly  be  summed  up  by  say- 
ing that  it  seems  probable  that  it  moves  in  some  mysterious  way, 
and  perhaps  the  phenomena  of  chemistry  arc  all  due  to  this  motion. 
But  that  carries  us  into  the  region  of  speculation  pure  and  simple, 
and  in  this  region  the  scientific  worker  feels  uncomfortable.  The 
atmosphere  is  too  rarefied  for  him. 
If  you  now  ask  what  is  the  soul  of  the  doctrine  of  atoms  ?  I  can 
only  answer  that  this  soul  is  still  in  the  course  of  development.  The 
doctrine  has  some  immortal  attributes,  but  what  will  live  after  its 
death  is  too  early  for  any  one  to  say. 
44  Prove  all  things.    Hold  fast  that  which  is  goodr 
