328 
MODIFICATION  OF  CHEMICAL  AFFINITY. 
Experiments  were  performed  with  a  view  to  determine  what 
effect  the  mass  of  water  might  have  on  the  salts  operated  upon ; 
its  influence  in  reducing  the  color  of  the  ferric  sulphocyanide 
was  found  to  be  very  great,  but  the  nature  of  it  could  not  be 
exactly  determined.  As,  however,  it  was  uniform  in  its  action  in 
whatever  manner  the  sulphocyanide  had  been  produced,  it  could 
not  affect  the  results  of  the  preceding  experiments.  Water  did 
not  appear  to  act  in  any  similar  manner  upon  the  other  ferric 
salts. 
From  the  mass  of  quantitative  observations  made  during  the 
investigation,  it  was  possible  to  deduce  not  only  the  order  of 
affinity  of  the  various  acids  for  sesquioxide  of  iron  as  compared 
with  potash,  but  also  to  assign  approximate  numbers.  Doubt 
may  rest  on  the  position  of  some  terms  in  the  series,  but  hydro- 
sulphocyanic  acid  certainly  had  the  least  affinity  for  ferric  oxide 
in  comparison  with  potash :  it  was  represented  by  unity :  the 
other  acids  followed  in  the  order — nitric,  4  ;  hydrochloric,  5 ; 
sulphuric,  7;  gallic,  10;  pyromeconic ;  meconic ;  acetic,  20; 
hydrobromic ;  comenamic  ;  citric,  100;  hydroferrocyanic  170. 
Other  colored  salts  were  submitted  to  a  more  cursory  investiga- 
tion. The  scarlet  bromide  of  gold  when  treated  with  an  alkaline 
chloride  gave  a  striking  instance  of  the  effect  of  mass  in  gradual- 
ly overcoming  a  strong  affinity.  The  intensely  red  iodide  of 
platinum  afforded  results  which,  though  somewhat  obscure,  were 
not  opposed  in  their  testimony.  So  did  the  blue  sulphate  of 
copper  when  treated  with  different  chlorides.  The  "manganoso- 
manganic  oxide"  dissolves  in  sulphuric  or  phosphoric  acid  of  a  red, 
and  in  other  acids  of  a  deep  brown  color ;  and  it  was  found  that 
hydrochloric  acid  was  capable  of  changing  the  color  of  the  sul- 
phate according  to  its  mass,  while  on  the  other  hand,  sulphuric  or 
phosphoric  acid  altered  in  like  manner  the  tint  of  the  chloride. 
Somewhat  similar  results  were  obtained  by  means  of  the  green 
chloride  and  the  purple  fluoride  of  molybdenum  ;  and  the  blue 
solution  that  forms  when  gallic  acid  is  brought  in  contact  with 
both  the  oxides  of  iron  at  once,  bore  testimony  to  the  same 
general  laws.  The  peculiar  optical  character  of  certain  salts  of 
quinine  was  also  taken  advantage  of  for  determining  what  changes 
took  place  among  the  compounds  in  solution.  The  amount  of 
fluorescence  exhibited  by  a  solution  of  acid  sulphate  of  quinine 
