Am,  Jour.  Pharm. 
July,  1889. 
Estimation  of  Hypophosphites. 
329 
salts,  the  following  manipulation  gave  very  good  results  with 
Ca(H2P02)2 :  O'l  to  0*2  gm.  are  dissolved  in  50  cc.  water,  10  cc. 
dilute  sulphuric  acid  and  sufficient  K2Mn2Os  added  until  the  liquid 
above  the  precipitated  hydrated  manganese  dioxide  has  a  distinct 
purple  color;  the  mixture  is  heated  to  60°C.  for  one-half  hour,  should 
the  supernatant  liquid  become  colorless  more  K2Mn208  must  be  added. 
By  addition  of  a  measured  quantity  of  normal  oxalic  acid  solution  the 
excessive  K2Mn208,  as  well  as  the  Mn02  H20,  is  reduced  and  a  color- 
less liquid  results  ;  to  this  is  now  added  sufficient  K2Mn208  to  produce 
a  permanent  pink  color.  From  the  total  K2Mn2Os  added  is  sub- 
tracted that  quantity  which  is  required  by  the  oxalic  acid,  the  re- 
mainder being  the  quantity  necessary  to  oxidize  the  hypophos- 
phite. 
5Ca(H2P02)2  -f  4K2Mn203  +  12H2S04=  5CaH4(P04)2  +  4K2S04+ 
850  1264 
■8MnS04+12H20. 
5H2C204.  2H20  +  K2  Mn208  +  3H2S04  =  10CO2  +  18H20  + 
630  316 
K2S044-2MnS04. 
316  parts  K2Mn2Os  are  the  equivalent  of  630.0   parts  H2C204.2H20 
"    "  "       "  212-5     "  Ca(H2P02)2 
"       "    «  "       Ci  165-0     "  H3P02 
"       "    "  "       "  260-2     "  KH2P02 
"  "       "    "  «       "  220-0     "  ]STaH2P02 
u    "  "       "  209-1      "  Fe2(H2P02)6 
While  with  Ca(H2P02)2  very  good  and  constant  results  were  ob- 
tained, the  method  applied  to  the  examination  of  KH2P02  and 
NaH2P02  was  not  very  satisfactory,  this  being  probably  due  to  the 
presence  of  chlorides  in  these  salts  ;  the  test  carried  out  in  neutral 
and  alkaline  solutions  gave  no  better  results. 
The  mercuric  chloride  method  was  now  the  one  which  had  to  be  relied 
upon  for  the  reducing  action  in  all  cases ;  some  experiments  were  made 
to  find  the  best  conditions.  If  mercuric  chloride,  in  excess,  be  added  to  a 
neutral  solution  of  a  hypophosphite  there  is  formed,  in  the  cold,  slowly 
a  precipitate  of  mercurous  chloride,  heating  promotes  the  precipitation, 
but  even  "then  it  requires  several  hours  for  complete  precipitation  ;  the 
addition  of  1  per  cent.  HC1  hastens  the  precipitation  which  is 
complete  after  heating  in  a  waterbath  for  thirty  to  forty-five 
minutes;  the  presence  of  15  per  cent.  HC1   causes   the  greater 
