%'ctob£"  imm'}        Detection  of  Emo  din-Bearing  Drugs.  445 
identification  of  other  drugs.  This  is  likely  to  be  the  case  with  cascara, 
senna,  and  other  emodin-bearing  drugs.  Ordinarily  the  emodin- 
bearing  drugs  as  a  class  would  be  detected  by  shaking  the  faintly 
acidified  extracts  with  benzol  and  washing  the  solvent  first  with  water, 
which  is  discarded,  and  then  with  very  dilute  ammonia  water.1  In 
presence  of  emodin  the  ammoniacal  layer  becomes  red,  the  depth  of 
color  and  shade  depending  somewhat  upon  the  amount  of  emodin 
present  and  the  source  of  the  drug  from  which  obtained.  This  test 
cannot  be  used  in  presence  of  phenolphthalein  because  this  substance 
behaves  like  emodin.  This  holds  true  in  spite  of  the  great  insolubility 
of  phenolphthalein  in  water,2  for  if  a  solution  containing  this  sub- 
stance be  acidified,  diluted  with  several  times  its  volume  of  water  and 
filtered,  the  filtrate  will  become  strongly  colored  purplish-red  on  the 
addition  of  ammonia  water  or  of  potassium  hydroxide  or  sodium 
hydroxide  solution.  Or  if  the  acid  filtrate  be  shaken  with  benzol,  the 
aqueous  layer  discarded,  and  the  solvent  washed  with  either  of  these 
alkaline  solutions,  the  purplish-red  color  appears  at  once.  Unless  the 
quantity  of  phenolphthalein  be  very  small  the  color  produced  by  it 
with  the  alkalies  will  hide  or  obscure  that  of  any  emodin  alkali  com- 
pounds that  may  be  present. 
Under  certain  conditions,  however,  the  color  produced  by  phenol- 
phthalein and  an  excess  of  the  fixed  alkali  hydroxides  gradually  dis- 
appears, owing  to  the  formation  of  the  trimetallic  salt  of  phenol- 
^orntrager:  Z.  anal  Chem.,  ig,  165  (1880). 
2  According  to  McCoy  (Am.  Chem.  Jour.,  31,  503,  1904),  the  maximum 
solubility  of  phenolphthalein  in  water  is  approximately  a  ten-thousandth- 
normal  solution.  This  is  equivalent  to  about  0.0032  Gm.  of  the  substance  in 
100  c.c.  This  conclusion  was  reached  after  approximate  determinations  had 
been  carried  out  by  two  methods.  In  one  0.0318  Gm.  of  purified  phenol- 
phthalein was  boiled  with  1200  c.c.  of  water.  On  cooling  no  deposit  formed, 
indicating  a  solubility  greater  than  twelve-thousandth-normal.  In  the  other 
known  amounts  of  tenth-normal  phenolphthalein  (in  alcohol)  were  added  to 
100  c.c.  of  five-hundredth-normal  ammonia  water  and  the  solution  neutralized 
by  the  addition  of  2  c.c.  of  tenth-normal  hydrochloric  acid.  With  0.5  c.c.  of 
the  phenolphthalein  solution  the  resultant  solution  contained  a  precipitate  of 
phenolphthalein ;  with  0.3  c.c.  the  solution  was  turbid ;  with  0.2  c.c.  faintly 
turbid ;  and  with  0.1  c.c.  clear,  although  a  slight  deposit  ^formed  on  standing 
over  night.  This  indicated  a  solubility  of  about  ten-thousandth-normal,  cor- 
responding to  0.00318  Gm.  per  100  c.c.  On  the  other, hand,  Zotier  (Bull.  soc. 
chim.  [4],  7,  993,  1910),  from  an  average  of  thirty  determinations  (method 
not  stated),  gives  the  solubility  of  phenolphthalein  in  water  as  about  0.0092 
Gm.  in  100  c.c. 
