*  Barium  Hypophosphorous

Sulphate.  Add.
Properties. — Hypophosphorous  acid  is  a  color'ess,  thick  liquid  of
strong  acid  reaction,  which  at  0°  forms  white  scales  fusing  at  17.4**.
When  heated,  it  decomposes  into  hydrogen  phosphide  and  phosphoric
acid.
^         2HPHaOa  -  PHs  HaPOi.
Because  of  its  great  affinity  for  oxygen,  being  oxidized  to  phosphoric
acid,  it  is  a  powerful  reducing  agent.  Thus  silver  nitrate  is  reduced  to
metallic  silver,  mercuric  chloride  to  mercurous  chloride,  copper  sulphate
to  its  hydride,  and  iodine  to  hydriodic  acid.
HPHaOa  4Hg(^la  aHaO  HaPOi       i       4H(1     -,      4HgCl.
HPHaOa  2la      ^       2HaO     .       HaPOi  4HI.
aHPHaOa     f     2CUSO4     '     4HaO  2H8PO4    -     CuaHa      :      2HaS04     -  Hi.
HPHaOa  2Cla      '       2HaO  H3PO4     -     4HCI.
sHPHaOa    -  4KMn04    i     6HaS04         2KaS04        4MnS04   -     5H8PO4        6HaO.
Acidum  Hypophosphorosum,  U.S. P.,  contains  30  per  cent,  by
weight  of  absolute  HPHgO^.  It  has  a  specific  gravity  of  about  1.130
at  25^

Acidum  Hypophosphorosum  Dilutum,  U.S.?.,  contains  :o  per
cent,  by  weight  of  absolute  HPHjO^.  This  acid  has  a  specific  gravity
of  about  1.042  at  25*^.
Impurities  and  Tests, — The  most  probable  impurities  in  this  acid
are  hydrochloric,  sulphuric,  phosphoric,  and  oxalic  acids,  barium,  arsenic,
and  calcium  hypophosphite.  Before  testing  for  the  presence  of  arsenic,
the  solution  must  be  oxidized  to  phosphoric  acid,  for  the  nascent  hydro-
gen generated  in  the  arsenic  test  reduces  the  hypophosphorous  acid  to
phosphine  gas  which  produces  a  yellow  stain,  similar  to  that  of  arsine,
upon  the  mercuric  chloride  paper  cap.    (U.S. P.  page  521.)

Hypophosphites. — The  salts  of  this  acid  are  prepared  from  the  cal-
cium or  barium  salt  by  double  decomposition.  They  are  all  soluble  in
water.
In  the  dry  state  they  are  stable,  but  in  solution,  when  exposed  to  the
air,  they  absorb  oxygen  and  are  gradually  oxidized  to  phosphates.
