328  Estimation  of  Hypophosphites.  {Am'j^yTm9&Tm' 
Ca(H2P02)2  were  dissolved  in  50  cc.  water,  1,0  cc.  dilute  sulphuric 
acid  (1-5)  added,  and  the  K2Mn208  allowed  to  run  in  from  a  burette  ; 
at  first  decolorization  occurred,  but  after  about  one-half  of  the  calcu- 
lated K2Mn2Os  had  been  added  the  solution  became  of  a  red  color, 
and  then  rapidly,  on  further  addition,  deposited  a  dark  brown  pre- 
cipitate of  hydrated  manganese  dioxide.  Repeating  this  experiment 
a  number  of  times  with  larger  quantities  of  sulphuric  acid,  also  by 
application  of  gentle  heat,  no  better  results  were  obtained.  Thinking 
that  the  reducing  action  would  progress  more  favorably,  if  a  ferric 
salt  was  present,  in  that  this  would  be  reduced  to  ferrous  salt  which, 
by  addition  of  K2Mn208,  could  be  easily  oxidized  to  the  ferric  condi- 
tion, an  addition  of  an  excess  of  ferric  sulphate  solution  was  made, 
and  after  boiling  and  allowing  to  cool  somewhat  the  K2Mn208  added  ; 
the  results  obtained  by  this  modification  did  not  differ  materially 
from  those  previously  mentioned.  It  maybe  opportune  to  here  men- 
tion the  peculiarity  of  hypophosphorous  acid ;  it  is  a  good  reducing 
agent  toward  permanganate  of  potassium  and  ferric  salts,  until  by  this 
action  it  has  been  changed  into  phosphorous  acid,  then  this  acid  re- 
duces permanganate  only  to  the  condition  of  hydrated  manganese 
dioxide,  the  ferric  salt,  even  upon  boiling,  being  very  slowly,  if 
at  all,  reduced  by  it.  The  proof  of  this  last  assertion  was  ob- 
tained by  boiling  the  hypophosphite  with  ferric  chloride  in 
moderately  dilute  acid  solution  until  no  further  decolorization  took 
place,  then  adding  an  excess  of  ferric  chloride  (sufficient  to 
impart  a  decided  color)  and  boiling  for  one  hour ;  by  addition 
of  ammonia  the  iron  was  precipitated ;  the  filtrate  strongly  re- 
duced mercuric  chloride  and  silver  nitrate  solutions ;  the  washings  of 
the  precipitate  for  a  long  time  reduced  silver  nitrate,  indicating  the 
presence  of  a  salt  of  a  reducing  acid  which  could  only  be  a  phos- 
phite ;  the  precipitate  was  dissolved  in  nitric  acid  and  solution  of 
molybdate  of  ammonium  added,  after  heating  for  some  time  to  40°C. 
the  mixture  deposited  so  little  precipitate,  that  it  was  possibly  due  to 
a  small  quantity  of  phosphite,  which  was  not  completely  removed  by 
washing,  and  which,  by  the  action  of  the  nitric  acid,  was  converted 
into  phosphate.  From  these  experiments  the  formation  of  phosphoric 
acid  from  hypophosphorous  acid  does  not  take  place  until  the  hypo- 
phosphorous  acid  has  been  completely  converted  into  phosphorous 
acid. 
After  understanding  the  peculiarities  of  the  two  acids,  and  their 
