614 
Iodine  in  Cod  Liver  Oil. 
/Am.  Jour.  Pharm- 
\       Dec,  1883. 
The  testings  are  performed  in  large  even  tubes  and  compared  with 
graduated  standard  solutions  of  potassium  iodide  treated  in  the  same- 
manner.  By  this  method  2"5"oi)  "oo"  P^^^  easily  detected  and  meas- 
ured, and  up  to  i  o^oVo"o"  P^^'^  ^^^^  estimation  is  very  accurate.  If  the 
iodine  in  a  seaweed  or  other  organic  substance  is  to  be  determined,  it 
is  carbonized  in  a  small  iron  retort  or  crucible,  and  the  charcoal  treated 
in  the  same  way.  Burning  to  ash,  however  carefully  done,  involves  a 
considerable  loss  of  iodine,  more  than  is  generally  supposed.  For 
instance,  a  sample  of  seaweed  ash  exposed  for  twenty-four  hours  in  an 
open  crucible  over  an  ordinary  Bunsen  burner  will  not  retain  a  trace 
of  iodine  at  the  end  of  that  time.  We  invariably  carbonize  the  mate- 
rial in  preference  to  burning  to  ash,  in  order  to  retain  all  the  iodine 
and  to  easily  extract  the  salts.  Some  of  these  specimens  are  extremely 
difficult,  indeed,  almost  impossible,  to  burn  to  complete  ash,  on  account 
of  the  large  proportion  of  fusible  salts  present.  In  estimating  the 
small  quantities  of  iodine  necessary  in  our  analyses  we  are  really  limited 
to  color  tests.  I  have  long  discarded  starch,  as  it  introduces  an  organic 
substance  very  liable  to  change,  and  in  many  cii'cumstances  unreliable. 
Moreover,  in  my  hands  it  is  not  so  sensitive  as  that  with  bisulphide  of" 
carbon.  The  solution  is  not  perfectly  transparent,  and  the  indications 
not  s(^  sharp.  The  color  is  spread  over  the  whole  liquid,  and  when  dilute 
can  only  be  seen  by  looking  down  the  length  of  the  tube,  whereas  in 
the  bisulphide  of  carbon  test  it  is  removed  out  of  the  solution  and 
concentrated  in  a  sixth  of  the  volume  at  the  bottom  of  the  tube.  The 
comparison  of  the  two  methods  is  very  marked.  In  testing  a  solution 
of  potassium  iodide  containing  only  2T0V oo"  P^^^  iodine,  the  maxi- 
mum effect  is  immediate,  and  another  advantage  is  that  the  iodine  can 
be  easily  separated  from  its  solution  in  bisulphide  of  carbon.  We 
usually  recover  the  latter  by  treating  it  with  zinc  in  the  presence  of 
water.  The  specimens  of  cod  liver  oil  experimented  on,  for  which  I 
am  indebted  to  our  mutual  friend  and  former  President,  Mr.  Keynolds,. 
were  taken  in  quantities  of  5,000  grains  each,  sa})onified  with  1,000 
grains  of  caustic  soda,  pure  and  free  from  iodine,  then  carbonized  in  a. 
large  porcelain  crucible ;  the  resulting  charcoal  was  treated  with  hot 
water  and  made  up  to  5,000  grains  measure.  One-tenth  of  this,  or 
500  grains,  was  found  quite  sufficient  to  detect  the  presence  of  iodine 
and  to  estimate  it.  Three  experiments  were  made,  taking  500  grains^ 
2,500  grains,  and  1,000  grains  respectively,  with  pretty  concordant, 
results.    The  mean  results  are  appended. 
