THE  AMERICAN 
JOURNAL  OF  PHARMACY 
APRIL,  ipoS 
PHOSPHORIC  ACID.1 
By  Prof.  Virgii,  Cobi.fnTz  and  Otto  B.  May,  Ph.D. 
A  criticism  has  been  made  that  the  percentage  strength  of  phos- 
phoric acid,  determined  by  the  present  alkalimetric  titration,  does 
not  give  results  in  accordance  with  those  obtained  from  the  specific 
gravity  and  its  table  (page  66 1,  U.S.P.).  Experiments  having  con- 
firmed this  criticism,  it  was  decided  to  investigate  our  official 
method,  in  addition  to  others,  which  might  be  available  for  phar- 
macopceial  purposes.  It  was  also  noted  that,  with  different  dilutions, 
the  percentage  strength  indicated  by  the  specific  gravity  did  not 
always  coincide  with  the  gravimetric  determinations.  These  will  be 
investigated  later.  For  the  following  experiments,  a  sample  of 
phosphoric  acid  fulfilling  the  US.P.  tests  for  purity  was  assayed 
gravimetrically.  This  contained  84  84  per  cent,  of  absolute  phos- 
phoric acid.  From  this  acid,  10  and  5  per  cent,  dilutions  were 
prepared  and  the  results  calculated  to  that  of  the  original  acid 
employed.  The  10  or  5  c.c.  employed  for  each  titration  was  care- 
fully measured  from  a  burette  and  titrated  with  normal  potassium 
hydroxide,  V.  S.,  using  phenolphthalein  as  indicator. 
1  This,  with  such  other  similar  publications  as  may  appear  in  the  columns 
of  the  Journai,  OF  Pharmacy,  represent  research  work  carried  out  by  Dr.  Otto 
May,  under  the  direction  of  V.  Coblentz,  chairman  of  the  Sub-corn tnittee  on 
Inorganic  Chemicals  of  the  Committee  of  Revision  of  the  U.S.  Pharmacopoeia. 
(ISO 
