^""oct"'i88o*""}  Preparation  of  Iodine- Iron  Cod  liver  Oil.  509 
when  the  mixture  is  shaken  with  diluted  starch,  not  even  if  to  the 
latter  should  be  added  a  solution  of  kalium  iodide.  The  addition  of 
kalium  iodide,  which  seizes  the  free  iodine  that  might  be  in  the  oil,, 
greatly  enhances  the  sensibility  of  the  amylum  reaction. 
I  prepare  my  codliver  oil  in  quantities  of  800  to  1,000  liters  in  a 
vessel  that  is  provided  with  a  stirring  apparatus,  and  several  cocks 
placed  in  gradual  elevations.  The  vessel  must  be  of  iron,  and  capable 
of  being  shut  hermetically.  During  the  preparation,  samples  of  the  oil, 
of  the  iodine  solution  and  of  the  iodine-iron  solution  are  sent  to  Prof. 
Vanderburg,  and  not  before  he  has  tested  them  is  the  operation  pro- 
ceeded with. 
In  large  quantities  French  iodine  is,  in  my  opinion,  to  be  preferred 
above  English  iodine.  The  latter  is  finer  and  consequently  mixed 
itself  easily  with  the  oil  to  a  tough  mass,  which  cannot  be  resolved 
again  but  with  great  difficulty.  In  small  quantities  the  solution  of  the 
iodine  may  be  considerably  quickened  by  pulverizing  the  iodine  in  a 
mortar.  A  long  shaking  with  iron  ought  not  to  be  omitted  in  this  case.. 
Though  apparently  all  the  iodine  is  dissolved  to  a  clear  liquid,  close 
investigations  have  shown  that,  especially  with  large  quantities,  small 
parts  of  a  dark  colored  matter  will  adhere  to  the  bottom  of  the  vessel, 
from  which  no  shaking  or  stirring  can  remove  them.  This  matter  is 
insoluble  in  ether.  It  may  be  nearly  completely  burnt.  The  eye,  with, 
the  aid  of  a  microscope,  can  detect  no  crystallization.  This  circum- 
stance probably  explains  why  the  iodine-iron  codliver  oil  is  of  a  finer 
taste  and  odor  than  the  original  oil. 
That  the  mixture,  after  its  purity  has  been  tested,  shows  a  free- 
iodine  reaction  when  it  has  stood  for  24  hours,  finds  its  explanation  in 
the  fact  that  a  small  quantity  of  ferrid-iodide  seems  to  have  been  pro- 
duced, which  soon  decomposes  itself  into  ferro-iodide  and  iodine.  The 
violet  color  owes  its  origin  to  the  small  particles  of  ferrid-oxyiodide,, 
which  can  hardly  be  avoided  but  by  a  very  careful  removal  of  the  air 
during  the  shaking  with  iron. 
A  preparation  that  should  be  totally  free  of  ferrid-oxyiodide  is  not  the 
thing  that  is  desired.  Then,  being  a  little  darker  colored  than  the 
oil  which  was  used,  it  obtains  immediately  after  it  has  been  brought 
into  contact  with  the  air  the  peculiar  dark  violet  color,  and  may  be 
used  as  a  sensible  characteristic  reagent  for  oxygen.  Without  taking 
this  precaution,  the  quantity  of  the  oxyiodide  combination  will  amount 
