510         Dr.  C.  R.  A.  Wright's  Reply  to  "An  Examination 
treated  by  an  appropriate  agent  undergoes  a  reaction  of  the  kind 
expressed  by  the  symbols 
X''C12  +  K0H=X''0  +  KC1  +  HC1, 
such  a  reaction  is  alluded  to  and  understood  by  the  phrase  "  0 
is  a  bivalent  symbol,  and  H  and  K  univalent  ones  in  formulae 
where  caustic  potash  and  its  derivatives  are  referred  to;"  in 
other  words,  the  valency  of  a  particular  radical  is  a  particular 
function  which  is  fixed  by  the  nature  of  the  reactions  which  the 
bodies  whose  formulae  contain  that  radical  are  capable  of  under- 
going. As  to  the  phrase  "  equivalent  quantity  of  a  radical,"  it 
is  self-evident  that  it  is  an  elliptical  expression.  To  take  a  case 
as  an  example,  the  reactions  of  water  show  that  0  is  a  bivalent 
symbol  and  H  a  univalent  one  in  such  reactions ;  hence  the  rela- 
tive equivalents  of  the  radicals  O  and  H  are  JJ?  and  {-,  or  8  and  1. 
Thus,  when  water  is  electrolyzed,  one  or  both  of  these  reactions 
ensue, 
2H20  =  2H2  +  02, 
3H20  =  3H2  +  03; 
that  is,  the  weights  of  hydrogen  and  oxygen,  or  hydrogen  and 
ozone,  are  always  found  to  be  in  the  proportions,  respectively, 
2(1x2)  to  (8x2)x2, 
or 
3(1x2)  „  (8x2)x3. 
Mr.  Atkinson  desires  that  I  should  account  for  the  differences 
between  isomeric  bodies.  This  is  a  problem  somewhat  beyond 
the  province  of  the  paper  which  Mr.  Atkinson  is  discussing,  the 
object  of  which  was  to  point  out  the  connexion  between  a  par- 
ticular hypothesis  and  certain  facts  expressed  in  symbols.  In 
that  paper  it  was  very  briefly  pointed  out  that  the  different  che- 
mical reactions  of  isomeric  substances  are  readily  expressed  by 
different  modes  of  dissection  of  the  same  formula.  The  limits 
of  the  paper  as  to  length  did  not  permit  a  full  discussion  of  the 
relations  of  the  atomic  hypothesis  to  isomerism ;  but  I  would 
now  ask,  Does  that  hypothesis  explain  isomerism  ?  or  is  it  not 
rather  opposed  to  what  little  is  known  on  the  subject  ?  On  this 
hypothesis,  isomeric  molecules  consist  of  the  same  number  of  the 
same  atoms,  but  in  different  relative  positions;  then,  either  the 
atoms  are  rigidly  connected,  or  they  have  a  limited  amount  of 
mobility  among  themselves:  they  cannot  be  perfectly  free  to 
move  in  all  directions ;  otherwise  the  molecule  would  not  hold 
together.  Now  all  our  notions  of  force,  and  the  observed  trans- 
formations of  potential  into  actual  energy,  or  the  reverse,  which 
take  place  in  chemical  reactions,  are  opposed  to  the  first  suppo- 
