Am Jul" r'i9i4arm' }     Determination  of  Phenolphthalein.  307 
A  NEW  METHOD  FOR  THE  DETERMINATION  OF 
PHENOLPHTHALEIN. 
By  Dr.  A.  Mtrkin,  Cincinnati,  O. 
Since  phenolphthalein  has  come  into  extensive  use  as  an  in- 
gredient of  laxative  medicines,  frequent  occasions  arise  for  its  rapid 
and  accurate  determination.  A  few  methods  have  been  proposed, 
but,  with  the  exception  of  one  (Pharm.  Zentrb.,  191 1,  p.  1126),  they 
are  all  gravimetrical,  therefore  troublesome  and  unreliable,  because 
applied  to  an  organic  substance. 
In  trying  to  find  a  volumetric  method  for  its  determination  I 
took  advantage  of  its  property  to  form  a  well-defined  oxime  with 
hydroxylamine.  This  is  the  principle  of  Walker's  method  for 
carvone  determination,  and  of  Nelson  and  his  estimation  of  a  number 
of  ketones,  including  camphor. 
I  first  followed  closely  the  directions  worked  out  by  the  above- 
mentioned  authors,  but  without  result.  I  then  worked  according 
to  Friedlander,  who  first  discovered  the  phenolphthalein  oxime,  but 
the  results  were  still  far  from  satisfactory.  Finally  the  following 
method  was  discovered,  the  results  of  which  are  very  accurate: 
1.  Gramme  phenolphthalein,  0.8  gramme  hydroxylamine  hydro- 
chloride, and  0.52  gramme  90  per  cent,  sodium  hydroxide  solution, 
finely  powdered,  are  dissolved  in  35  to  40  c.c.  of  absolute  alcohol 
and  boiled  for  two  to  three  hours  under  a  reflex  condenser  until  the 
liquid  turns  yellow.  The  liquid  is  then  diluted  with  water,  trans- 
ferred to  a  250  c.c.  volumetric  flask,  10  c.c.  of  10  per  cent.  H2S04 
are  added  and  the  flask  filled  to  the  mark  with  water.  50  C.c.  are 
taken  for  titration.  First  the  acid  is  neutralized,  using  Methyl 
orange  as  indicator.  Then  the  excess  of  hydroxylamine  is  titrated 
with  N/10KOH,  using  phenolphthalein  as  indicator.  A  blank  is 
run,  using  the  same  amounts  of  hydroxylamine,  NaOH  and  alcohol, 
and  boiled  for  the  same  length  of  time.  The  difference  in  the 
number  of  cubic  centimetres  of  N/10  alkali  used  in  the  titration  of 
the  blank  experiment  and  in  the  sample,  multiplied  by  316,  gives  the 
quantity  of  phenolphthalein. 
When  applying  the  method  to  medicinal  tablets,  the  tablets  were 
placed  in  a  cylinder  and  crushed  under  alcohol  with  a  glass  rod. 
The  alcohol  was  decanted  off  through  a  filter  into  a  volumetric  flask 
