270 
Assay  of  Ferric  Hypophosphite. 
Am.  Jour.  Pharm. 
June,  1891. 
ASSAY  OF  FERRIC  HYPOPHOSPHITE. 
By  Frank  X.  Moerk,  Ph.G. 
Contribution  from  the  Chemical  Laboratory  of  the  Philadelphia  College  of  Pharmacy.— 
No.  88. 
Read  at  the  Pharmaceutical  Meeting  of  the  Philadelphia  College  of  Pharmacy,  May  19. 
In  previous  papers  (Am.  Journ.  Pharm.,  1889,  326  and  386)  on 
"  The  examination  of  officinal  hypophosphites,"  several  methods 
for  estimating  these  salts  were  described  :  (1)  With  potassium 
permanganate  ;  (2)  with  mercuric  chloride  and  (3)  with  sodium 
hydrate,  after  oxidation  with  bromine ;  I  and  3  are  volumetric 
methods,  while  2  is  a  gravimetric  method.  Of  these  methods 
the  second  one  was  stated  to  be  the  more  likely  one  to  be  used  in 
stores,  although  requiring  much  more  time  than  the  other  methods. 
In  the  examination  of  ferric  hypophosphite  it  was  found  at  that 
time  that  correct  results  were  not  obtainable,  working  under  the 
same  conditions  as  with  the  other  hypophosphites  and  for  this  salt  the 
third  method  was  recommended.  The  difficulty  explained  already 
at  that  time,  was  due  to  the  oxidation  of  the  hypophosphite  (with 
reduction  of  the  ferric  salt)  in  obtaining  the  salt  in  solution. 
Recently  I  have  made  some  further  experiments  with  this  method 
with  the  result  that  I  was  able  to  successfully  estimate  this  hypo- 
phosphite with  mercuric  chloride  ;  the  details  are  as  follows  : 
0-2  finely  powdered  ferric  hypophosphite,  t-o  citric  acid  and  25  cc. 
water,  are  placed  in  a  beaker  and  stirred  for  several  minutes  until 
the  acid  dissolves  ;  then  ammonia  water  is  added  slowly  until  the 
liquid  smells  strongly  of  it  (this  has  for  its  object  the  decomposition 
of  the  ferric  hypophosphite,  the  ferric  hydrate  entering  largely 
into  solution  through  the  agency  of  the  ammonium  citrate  present) ; 
after  allowing  to  stand  for  ten  minutes  with  frequent  stirring  to 
completely  decompose  the  iron  salt,  75  cc.  of  a  cold  saturated  solution 
of  mercuric  chloride  are  added  and  then  hydrochloric  acid,  drop  by 
drop,  stirring  constantly  until  an  almost  colorless  solution  results  and 
the  calomel  commences  to  precipitate  (before  the  addition  of  the  mer- 
curic chloride  the  solution  is  of  a  brownish  color,  generally  contain- 
ing a  little  ferric  hydrate  suspended;  the  mercuric  chloride  solution 
causes  a  heavy  white  precipitate,  which  by  the  addition  of  a  few 
drops  of  hydrochloric  acid  dissolves  again,  forming  a  brownish  or 
greenish  solution ;  the  addition  of  more  acid  gradually  produces 
decoloration ;    as  soon  as   the  liquid  becomes  colorless  separa- 
