Amji°ne"-i£iarin'}       Assay  of  Ferric  Hypophosphite.  271 
tion  of  calomel  commences),  allow  to  stand  for  one-half  hour  and 
then  place  for  a  further  half-hour  in  a  water-bath  at  ioo°  C.  Col- 
lect the  precipitate  upon  a  weighed  filter,  wash  with  boiling  water, 
dry  at  100°  C.  and  weigh.  The  weight  of  the  calomel  multiplied 
by  -088934  gives  the  weight  of  the  ferric  hypophosphite.  With 
the  same  sample,  after  the  details  were  ascertained,  the  following 
percentage  figures  were  obtained:  97*56,  9773  and  97-73. 
With  this  sample  similar  results  were  arrived  at  in  the  following 
manner  :  0-2  gm.  ferric  hypophosphite  was  dissolved  in  3-5  cc. 
concentrated  hydrochloric  acid,  50  cc.  water  added,  and  heated 
in  a  water-bath  for  one-half  hour;  then  add  75  cc.  cold  saturated 
solution  of  mercuric  chloride  and  place  in  the  water-bath  for  a 
further  half-hour,  etc.,  as  in  the  previous  description. 
Fe2(H2P02)6  requires  for  complete  oxidation  twelve  oxygen 
atoms  ;  one  molecule  of  any  ferric  salt  in  its  reduction  to  ferrous  salt 
gives  up  one  oxygen  atom  : 
Fe2(H2P02)  6+  H20  =  2Fe(H2P02)2  +  2H3P02  +  O 
This  oxygen,  of  course,  is  taken  up  by  the  hypophosphorous  acid 
rendering  it  necessary  to  take  up  only  eleven  from  the  mercuric 
chloride  ;  hence  the  weight  of  mercurous  chloride  obtained  in  this 
method  must  be  increased  by  one-eleventh  so  as  to  express  the 
hypophosphite  present. 
The  results  by  this  method  will  be  high  if  the  ferric  salt  be  not 
completely  reduced  to  ferrous  salt.  Working  by  the  above  direc- 
tions the  following  percentage  figures  were  obtained  :  97*45,  97-60 
and  97-56. 
An  estimation  of  the  phosphoric  acid  yielded  by  oxidation  with 
bromine  (Amer.  Jour.  Pharm.,  1889,  330)  and  calculating  to  ferric 
hypophosphite  indicated  97*73  per  cent,  of  the  latter  in  the  salt 
examined. 
From  these  determinations  it  appears  that  the  alkaline  citrate 
prevents  the  hypophosphorous  acid  from  exerting  any  reducing 
action  upon  the  ferric  salt  in  the  time  necessary  for  making  the 
assay ;  the  important  point  to  be  observed  is'  to  first  allow  the 
greater  part  of  the  reduction  to  take  place  in  the  cold  and  then  to 
finish  by  application  of  heat.  The  filtrate  should  always  be  tested 
by  heating  to  the  boiling  point,  to  see  if  the  reduction  is  complete- 
In  the  Journal  of  the  Society  of  Chemical Indtistrics,  1 89 1,  68,  is  an 
