52  Precipitation  of  Quinia,  etc,  {^^Veh^Xi^rL^^ 
the  latter  salt  having  been  effected  with  just  enough  dilute  sulphuric 
acid.  A  white  precipitate  was  the  result,  doubtless  owing  to  the 
presence  of  some  quinidia  in  the  quinia  salt ;  for  a  solution  of  one 
part  of  quinia  sulphate  in  40  of  water,  effected  with  a  sufficient  quan- 
tity of  sulphuric  acid,  remained  clear  on  the  addition  of  iodide  of 
potassium  in  substance.  When  a  considerable  excess  of  pure  sulphu- 
ric or  muriatic  acid  w\as  used  for  dissolving  the  quinia,  the  addition 
of  solution  of  potassium  iodide  occasioned  no  turbidity  or  sediment ; 
therefore  the  observation  of  Righini  is  not  correct  as  far  as  it  relates 
to  neutral  potassium  iodide. 
A  solution  of  sulphate  of  quinia  (1*40)  with  just  sufficient  acid  was 
prepared,  iodide  of  potassium  added,  and  then  solution  of  citrate  of 
iron  ;  a  white  turbidity  with  the  gradual  production  of  a  bright  red 
precipitate  was  the  result. 
The  same  quinia  solution  was  made,  except  that  a  considerable 
excess  of  dilute  sulphuric  acid  was  used ;  after  the  solution  of  iodide 
of  potassium  had  been  effected,  every  drop  of  the  solution  of  iron 
citrate  occasioned  a  brownish  white  precipitate,  which  rapidly  changed 
through  various  shades  into  deep  brown.  If  the  order  of  mixing  was 
reversed,  the  potassium  iodide  yielded  with  dilute  sulphuric  acid  a 
colorless  solution,  wdiich  became  turbid  and  turned  brown  with  the 
iron  citrate,  and  now  yielded  with  solution  of  quinia  a  darker  colored 
precipitate,  changing  more  readily. 
If  an  aqueous  solution,  or  the  tincture  of  sesquichloride  of  iron, 
diluted  with  water  so  that  the  iron  color  can  scarcely  be  perceived,  is 
mixed  with  solution  of  potassium  iodide,  an  iodine  color  is  at  once 
produced,  doubtless  owing  to  the  formation  of  ferric  iodide :  Fe2Cl3+ 
3KI=Fe2l3+3KCl.  But  since  in  a  mixture  of  solutions  of  different 
salts  the  acid  and  bases  interchange  in  part,  provided  an  insoluble 
compound  be  not  formed,  a  mixture  of  the  two  solutions  must  contain 
Fe2Cl3,  Fe2l3,  KI  and  KCl ;  the  third  equivalent  of  iodine  in  Fe2l3 
being  but  loosely  combined,  we  have  in  the  above  mixture  practically 
KI2,  and  obtain  with  it  in  quinia  solutions  the  same  precipitate  which 
we  observe  on  the  addition  of  Lugol's  solution. 
The  appearance  of  the  red  or  brown  precipitate  which,  according  to 
Righini,  contains  quinia,  hydriodic  acid  and  iodine,  depends  therefore 
on  the  presence  of  KI2,  or  if  KI  be  used,  on  the  presence  of  some 
other  compound  producing  the  former. 
The  precipitate  obtained  in  putting  up  the  above  prescription,  after 
