MODIFICATION  OF  CHEMICAL  AFFINITY. 
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was  never  converted  into  the  red  salt ;  that  the  amount  of  it  so 
converted  depended  on  the  nature  both  of  the  acid  combined  with 
the  ferric  oxide,  and  of  the  base  combined  with  the  sulpho- 
cyanogen  ;  and  that  it  mattered  not  how  the  bases  and  acids  had 
been  combined  previous  to  their  mixture,  so  long  as  the  same 
quantities  were  brought  together  into  solution.  The  effect  of 
mass  was  fully  tried  by  mixing  equivalent  proportions  of  ferric 
salts  and  sulphocyanides,  and  then  adding  known  amounts  of 
either  one  or  the  other  compound.  It  was  found  that  in  either 
case  the  amount  of  red  salt  was  increased  ;  and  that  when  the 
numbers  of  equivalents  of  the  salt  added  were  taken  as  abscissae, 
and  the  amounts  of  red  sulphocyanide  produced,  as  ordinates, 
the  numbers  observed  in  the  experiments  gave  regular  curves, 
though  not  belonging  to  the  second  order.  The  curves  repre- 
senting the  experiments  in  which  sulphocyanide  of  potassium  was 
mixed  with  ferric  nitrate,  chloride,  or  sulphate,  appeared  to  be 
the  same,  but  hydrosulphocyanic  acid  gave  a  different  curve. 
The  deepest  color  was  given  when  nitrate  of  iron  was  mixed  with 
the  sulphocyanide,  but  even  upon  the  admixture  of  one  equiva- 
lent of  the  former  with  three  of  the  latter,  only  0-194  equiv.  of 
the  intensely  red  ferric  salt  was  formed,  and  when  375  equiva- 
lents of  sulphocyanide  of  potassium  had  been  added,  there  was 
still  a  recognizable  amount  of  nitrate  of  iron  undecomposed.  It 
was  found  that  the  addition  of  a  colorless  salt  not  only  reduced 
the  color  of  a  solution  of  ferric  sulphocyanide,  but  also  that  the 
reduction  increased  in  a  regularly  progressive  ratio  according  to 
the  mass  of  the  salt. 
Other  ferric  salts  were  likewise  examined.  The  black  gallate 
gave  results  precisely  analogous  to  those  obtained  by  means  of 
the  sulphocyanide ;  the  red  meconate  also  confirmed  Berthollet's 
views,  but  the  action  of  mass  was  rendered  obscure  by  the  for- 
mation of  double  or  of  acid  salts;  the  red  pyromeconate  resem- 
bled the  meconate  ;  the  red  acetate  bore  similar  testimony ;  the 
blue  solution  of  the  ferric  ferrocyanide  in  oxalic  acid  gave  results 
fully  corroborative  of  the  influence  both  of  the  nature  and  of  the 
mass  of  every  substance  present  at  the  same  time  in  the  mixture  ; 
the  purple  and  the  red  comenamate  afforded  similar  results;  while 
the  red  bromide  (not  the  oxybromide,)  though  somewhat  indis- 
tinct in  its  testimony,  corroborated  to  a  certain  extent  the  pre- 
ceding observations. 
