AmjJ^1|5arm-}        Estimation  of  Hypophosphites.  327 
ance  of  acetic  acid,  cause  a  white  precipitate  with  lead  acetate.1  These 
tests,  however,  appear  to  be  valueless  for  quantitative  estimations. 
To  estimate  hypophosphites  the  same  methods2  are  recommended 
as  for  the  estimation  of  phosphites  ;  they  are  two  in  number :  1,  Con- 
version of  the  acids  or  salts  into  phosphoric  acid  or  phosphate,  esti- 
mating this  and  calculating  then  to  the  acid  or  salt  used ;  2,  Deter- 
mination of  the  reducing  action  by  use  of  mercuric  chloride  in  excess, 
weighing  the  mercurous  chloride  formed,  and  calculating  to  original 
substance.  While  these  methods  give  good  results,  if  working  with 
pure  substances,  no  mention  is  made  of  the  determiuation  of  both  in  a 
mixture. 
By  carefully  studying  these  two  methods  the  following  process  was 
devised,  for  a  correct  understanding  of  which  the  essential  reactions 
are  first  given  : 
H3P02+4HgCl2+2H20=H3P04+2Hg2Cl2-f4HCl  and 
2H3P03+4HgCl2+2H20=2H3P04+2Hg2C]2+4HCl. 
It  will  be  seen  that  hypophosphorous  acid,  H3P02,  has  twice  the 
reducing  action  of  phosphorous  acid,  H3P03;  hence,  should  H3P03  be 
present  with  H3P02,  two  molecules  H3P03  will  always  be  expressed  as 
one  molecule  H3P02.  By  oxidation,  however,  the  two  molecules  of 
H3P03  will  form  two  molecules  of  H3P04,  which  by  the  first  method 
will  then  be  calculated  as  two  molecules  of  H3P02 ;  so  by  this  deter- 
mination a  larger  amount  of  H3P02  will  be  obtained  compared  with 
that  found  by  the  reducing  action,  and  this  excess  will  represent  one 
molecule  of  H3P02  formed  from  two  molecules  of  H3P03 ;  the  calcu- 
lation as  H3P03  can  then  be  made  by  the  proportion : 
H3P02  :  2  H3PO3  :  :  the  difference :  x. 
A  better  method  of  determining  the  reducing  action  it  was  thought 
could  be  found  by  using  an  acid  solution  of  permanganate  of  potas- 
sium ;  this  method,3  has  at  various  times  been  mentioned  as  a  good 
one  for  the  estimation  of  hypophosphites,  but  matters  apparently  rested 
with  the  mentioning,  as  no  account  of  the  details  could  be  found  after 
a  careful  search.  In  the  following  experiments  calcium  hypophosphite 
was  used  ;  the  K2Mn208  solution  was  made  by  dissolving  5  gm.  in  a 
liter  of  distilled  water,  and  this  solution  was  standardized  by  means 
of  the   normal   solution  of  oxalic  acid.    From   0*1  to  0*2  gnu 
1  Fresenius  :  Qualitative  Analysis. 
2  Watts'  Dictionary  of  Chemistry. 
3  Amer.  Jourx.  Pharm.,  1882,  138  and  1887,  246. 
