446  The  Detection  of  Emo  din-Bearing  Drugs.  {A™'cto™r  Su™' 
phthalein,  leaving  the  solution  colorless.  On  the  other  hand,  the  color 
of  the  alkali  compounds  with  emodin  is  more  stable,  sometimes  last- 
ing for  several  days.*  An  attempt  was  made  to  differentiate  by  this 
test  between  phenolphthalein  and  emodin  when  in  mixture,  but 
the  results  were  not  very  satisfactory.  If  applied  to  a  mixture  of 
phenolphthalein  and  an  extract  of  an  emodin-bearing  drug,  obtained 
by  extraction  with  alcohol  and  evaporation  of  the  solvent,  the  ex- 
tracted coloring  matter  renders  the  test  worthless.  If  applied  to  a 
benzol,  chloroform,  or  ether  extract,  the  confusion  of  colors  renders 
positive  identification  doubtful.  However,  if  the  red  color  of  the 
strongly  alkaline  solution  disappears  the  test  is  a  valuable  confirma- 
tion of  the  absence  of  most  of  the  emodin-bearing  drugs.  If  the 
color  persists  after  standing  for  several  hours,  the  presence  of  an 
emodin-bearing  drug  is  presumptive.  A  method  seemed  desirable 
by  which  the  phenolphthalein  might  be  removed  from  such  mixtures, 
thus  leaving  the  emodin  free  to  be  tested  for  in  the  usual  way.  Of  the 
several  methods  used  for  its  quantitative  determination,  that  proposed 
by  Kollo,3  by  which  the  substance  is  precipitated  as  tetraiodophenol- 
phthalein,4  seemed  the  most  promising. 
Some  tests  were  first  made  with  a  preparation  known  to  contain 
phenolphthalein  (most  of  which  was  in  suspension)  and  an  emodin- 
bearing  drug  extract. 
The  following  method  was  used : 
The  preparation,  which  was  in  the  form  of  a  syrup,  was  diluted 
with  water,  faintly  acidified  and  filtered  to  remove  most  of  the  phenol- 
phthalein. The  filtrate  was  neutralized  with  ammonia  water,  evap- 
orated to  a  very  thick  syrup,  and  the  warm  syrup  extracted  with 
acetone  (which  had  been  rendered  slightly  acid  by  hydrochloric  acid) 
by  stirring  with  successive  small  portions  of  the  solvent  and  decanting 
from  the  residue.  In  this  case  acetone  was  found  a  more  suitable 
solvent  than  either  chloroform  or  ether,  as  it  formed  less  troublesome 
emulsions.  In  preparations  that  do  not  form  emulsions  ether  extracts 
are  more  satisfactory  for  the  subsequent  manipulations.  The  acetone 
fractions  were  united,  evaporated  to  dryness  on  the  water-bath,  the 
*  Experiments  have  shown  that  if  ether  extracts  from  small  amounts 
of  rhubarb  be  heated  on  the  water-bath  for  three  hours  with  50  per  cent, 
sodium  hydroxide  solution  the  red  color  is  not  destroyed. 
sAp.  Ztg.,  24,  283  (1909). 
4  Tetraiodophenolphthalein  was  first  described  by  Classen  and  Loeb  (Ber., 
28,  1603,  1895). 
