382 
Contact  Actions. 
Am.  Jour.  Pharm. 
Aug.,  1886. 
inent,  or  decomposition.  These  changes  are  accompanied  by  an 
alteration  of  the  energy  of  the  system,  but  although  the  total  heat 
effect  observed  is  the  algebraical  sum  of  the  energy  changes,  con- 
ditioned by  the  several  changes  of  motion,  yet  thus  far  it  is  not 
possible  to  assign  to  each  particular  change  its  peculiar  heat  effect. 
As  an  example  of  chemical  changes  induced  by  the  mere  superficial 
contact  of  the  molecule  as  a  whole,  the  author  quotes  the  well-known 
experiments  of  Spring  on  the  combination  of  metals  with  sulphur  by 
mere  pressure. 
Thirdly. — The  motion  of  the  atoms  within  the  molecule  taken  by 
itself  can  be  of  such  a  kind  as  to  produce  a  chemical  change  or 
formation  of  a  molecule  of  a  different  kind,  such  as  the  so-called 
isomeric  transformation.  Or  again,  the  superficial  contact  of  B  with 
A,  a  mixture  of  heterogeneous  molecules  may  cause  either  a  decom- 
position or  a  combination  between  them,  as  exemplified  in  the  experi- 
ments of  Hautefeuille  and  Lemoine,  which  demonstrate  that  the 
presence  of  porous  substances  can  induce  the  combination  of  hydrogen 
with  iodine,  and  conversely  the  decomposition  of  hydriodic  acid,  both 
reactions  attaining  a  limit.  Of  a  similar  nature  is  the  combination 
of  hydrogen  with  oxygen,  induced  by  contact  with  finely  divided 
platinum,  and  also  the  recent  experiments  of  Konovaloff  on  the 
decomposition  of  haloid  derivatives  of  pentane  by  contact  with 
materials  in  a  state  of  fine  division.  These  phenomena  are 
generally  classified  under  the  title  of  catalytic  or  contact  actions. 
Such  can  only  be  explained  on  the  hypothesis  that  a  stable  substance 
B  is  in  such  a  condition  that  a  moderate  perturbation  of  the  constitu- 
ent atoms  at  its  superficies  produce  no  disturbance  in  the  atom- 
equilibrium  of  the  molecule;  whilst  in  the  case  of  a  changeable 
substance  A,  the  equilibrium  of  atoms  within  the  molecule  is  of  such 
a  kind  that  a  comparatively  unimportant  change  of  motion  at  the 
superficies  can  cause  the  atoms  to  assume  a  different  form,  that  is  to 
say,  can  cause  the  production  of  a  different  kind  of  matter.  If  this 
be  a  correct  representation  of  these  contact  phenomena,  then  the 
induced  reactions  should  either  be  accompanied  by  a  slight  heat 
change,  or,  if  accompanied  by  a  considerable  heat  change,  then  the 
reaction  should  be  capable  of  proceeding  by  itself  in  the  direction  of 
the  heat  evolution.  An  example  of  the  former  case  is  the  reaction 
between  hydrogen  and  iodine  ;  of  the  latter  is  the  system  of  hydrogen 
with  oxygen  in  contact  with  platinum,  which  causes  a  lowering  of 
