NOTE  ON  SYRUP  OF  HYPOPIIOSPHITE  OF  IRON.  343 
processes  it  is  necessary,  as  a  starting  point,  to  have  a  solution 
of  hypophosphorous  acid  of  some  defined  and  uniform  strength. 
In  Parrish's  book  a  formula  is  given  for  the  production  of  this 
acid.    It  is  as  follows  : — 
Take  of  hypophosphite  of  lime,  480  grs.  ;  crystallized  oxalic 
acid,  350  grs.  or  q.  s.  ;  water,  9  fl.  oz.  Dissolve  the  hypophos- 
phite in  6  oz.  of  the  water,  and  the  acid  in  the  remainder  with 
the  aid  of  heat;  mix  the  solutions,  pour  the  mixture  on  a  white 
paper  filter,  and  when  the  liquid  has  passed,  add  distilled  water 
carefully,  till  it  measures  10  fl.  oz.,  and  evaporates  this  to  8J  fl. 
oz.  The  solution  thus  prepared  is  stated  to  contain  about  10 
per  cent,  of  real  acid  (HPH202). 
Having  frequent  occasion  to  prepare  this  hypophosphite  of 
iron,  I  at  first  resorted  to  the  process  given  by  Mr.  Parrish,  and 
made  a  quantity  of  the  hypophosphorous  acid  by  his  method  as 
just  described.  But  upon  carefully  testing  the  acid  I  obtained,  I 
found  it  was  not  so  pure  as  theory  would  indicate  it  should  be ; 
in  fact,  it  contained  an  appreciable  quantity  both  of  oxalic  acid 
and  of  lime.  The  free  hypophosphorous  acid  had  dissolved  a 
portion  of  the  oxalate  of  lime.  This  impurity  seemed  to  me  to 
be  of  some  importance,  and,  as  it  could  not  be  got  rid  of,  it 
constituted  an  objection  to  the  process.  It  was  easy  to  produce 
a  purer  acid  by  resorting  to  hypophosphite  of  baryta,  and  exactly 
decomposing  its  solution  with  sulphuric  acid.  But  as  the  syrup 
of  hypophosphite  of  iron  is  only  occasionally  demanded,  and  as, 
from  its  proneness  to  oxidation,  it  deteriorates  greatly  by  long 
keeping,  it  appeared  desirable  to  possess  a  more  expeditious 
method  for  its  preparation  than  that  which  involves  the  elimina- 
tion of  the  acid,  and  precipitation  of  the  iron  as  carbonate.  I 
consequently  abandoned  the  use  of  the  acid,  and  resorted  to  a 
process  of  double  decomposition. 
When  hypophosphite  of  lime  and  sulphate  of  iron  are  brought 
into  contact,  sulphate  of  lime  is  precipitated,  and  ferrous  hypo- 
phosphite remains  in  solution. 
Ca(PH262)24-FeS04-Fe(FH202)2+CaS04. 
Using  these  materials  in  their  atomic  proportions,  the  iron 
salt  is  obtained  contaminated  only  by  a  small  quantity  of  sul- 
phate of  lime,  and  the  amount  of  the  latter  may  be  reduced  to 
a  minimum  J>y  employing  very  little  water  as  a  solvent. 
