43^  Scammony  and  Resin  Scamniony.  {^ttmbe^tm' 
easily  seen.  About  one-tenth  of  a  gramme  more  of  iodine  is  added, 
until  the  dark  color  of  the  solution  is  partly  restored.  This  is  done 
to  prevent  the  solution  containing-  an  excess  of  chlorine.  To  make 
a  determination,  i  Gm.  of  the  powdered  resin  is  put  into  a  glass- 
stoppered  200  c.c.  bottle,  10  c.c.  of  redistilled  carbon  tetrachloride 
free  from  carbon  disulphide  or  oxidizable  substances  are  added,  and 
25  c.c.  of  the  iodine  monochloride  solution.  After  standing  for  one 
hour  in  the  dark,  20  c.c.  of  10  per  cent,  potassium  iodide  solution 
are  added  and  50  c.c.  of  distilled  water,  and  the  excess  of  iodine 
titrated  back  in  the  usual  way.  The  end-point  is  very  sharp  and 
there  is  very  little  tendency  for  the  blue  color  to  reappear.  One 
sample  which  was  allowed  to  stand  for  15  hours  required  only 
0.3  c.c.  more  of  tenth-normal  thiosulphate  solution  to  titrate  the 
iodine  which  had  separated. 
The  iodine  numbers  obtained  by  Wijs's  method  were  in  every  case 
higher  than  those  obtained  by  Hiibl's  method,  even  when  the  latter 
solutions  were  allowed  to  stand  for  twenty-four  hours.  Blank  de- 
terminations are  unnecessary  with  Wijs's  method.  The  equivalent 
of  25  c.c.  of  the  solution  in  terms  of  sodium  thiosulphate  solution  is 
determined  once  for  alb  and  the  solution  is  so  stable  that  subsequent 
blanks  are  not  necessary.  The  solution  of  iodine  monochloride  can 
be  prepared  in  one-half  hour,  and  for  most  oils  and  fats  from 
fifteen  to  fort}'  minutes  is  sufficient  time  for  complete  absorption 
of  the  iodine.  The  behavior  of  the  scammony  resins  toward  Hiibl's 
solution  led  us  to  consider  one  hour  as  a  sufficient  time,  but  it  may 
be  said  that  no  difference  was  found  when  the  absorption  was  con- 
tinued for  one-half  hour  longer. 
The  optical  rotations  were  determined  with  the  decolorized 
resin  in  the  following  way :  about  4  Gm.  of  the  resin  were  dissolved 
in  about  50  c.c.  of  alcohol,  water  added  almost  to  turbidity,  and  the 
solution  boiled  for  one  hour  with  about  2  Gm.  of  animal  charcoal, 
using  a  reflux  condenser.  After  settling,  the  solution  is  cooled,  and 
the  liquid  poured  through  a  filter.  A  second  treatment  with  animal 
charcoal  generally  suffices  to  give  a  solution  which  is  almost  color- 
less. After  filtering,  10  c.c.  of  this  _  solution  are  removed  by  a 
pipette  to  a  small  tared  beaker,  evaporated  to  dryness,  dried  at 
1100  and  weighed.  Another  portion  of  the  solution  is  polarized 
in  a  10  cm.  tube. 
In  order  to  confirm  the  results  of  previous  observers,  and  to 
orient  ourselves  regarding  virgin  scammony  and  Mexican  scammony 
