330 
Estimation  of  Hypophosphites. 
Am.  Jour.  Pharm. 
July.  1889. 
part  of  the  reduction  to  take  place  in  the  cold  in  a  few  minutes, 
but  heating  in  a  waterbath  for  twenty  to  thirty  minutes  is  essential 
for  complete  precipitation.  As  Hg2Cl2  is  liable  to  change  by  heating 
with  moderately  strong  HC1,  the  following  manner  of  employing  the 
test  was  used  :  0*2  to  0*3  gm.  of  the  hypophosphite  were  dissolved  in 
25  cc  water  (ferric  hypophosphite  formed  an  exception  to  this  method  ; 
for  details  see  that  compound),  1  cc  HC1  and  75  cc  of  a  saturated  solu- 
tion of  mercuric  chloride  added,  heated  in  a  waterbath  for  45  to  60 
minutes,  filtered  through  a  weighed  filter,  and  the  nitrate  heated  to 
the  boiling  point  for  several  minutes ;  if  no  further  precipitation 
takes  place,  the  precipitate  is  well  washed  with  boiling  water,  dried  at 
100°  and  weighed.  Should  a  precipitate  form  the  heating  must  be 
continued  for  fifteen  minutes  and  nitration  repeated.  A  large  num- 
ber of  determinations  made  by  this  method  did  not  furnish  a  single 
case  in  which  a  second  precipitation  occurred. 
The  weight  of  mercurous  chloride  multiplied  by  the  following 
factors  (obtained  by  writing  the  reactions  and  dividing  the  molecular 
weights  of  the  hypophosphites  by  the  amount  of  Hg2Cl2  formed  from 
them),  will  give  the  amount  of  the  hypophosphite  : 
For  H3P02  multiply  by  0-070183 
"    NaH2P02     «       «  0-093577 
"    KH2P02     "       "  0-110697 
«    Ca(H2P02)2  "       u  0-090387 
"    Fe2(H2P02)6"       "  0-088934 
The  second  part  of  the  determination  consists  in  oxidizing  the  hypo- 
phosphite and  estimating  the  phosphoric  acid  formed  ;  experiments 
proved  that  bromine  is  the  best  oxidizing  agent  that  can  be  used. 
From  0'2  to  0'3  gm.  of  the  hypophosphite  are  dissolved  in  50  cc.  water, 
a  few  drops  bromine  added  and,  after  covering  the  beaker,  moderate 
heat  applied  ;  should  the  solution  become  colorless,  more  bromine  must 
be  added  and  the  heating  continued  ;  after  the  solution  has  retained 
the  bromine  color  for  half  an  hour,  it  is  heated  to  the  boiling  point, 
and  by  occasionally  lifting  the  cover  the  bromine  vapors  are  allowed 
to  dissipate.    An  excess  of  ammonium  hydrate  is  now  added,  and  if  a 
precipitation  of  phosphate  occurs  (as  there  will  be  if  the  calcium 
or  ferric  salt  has  been  used  or,  if  in  the  preparation  of  the  alkaline 
hypophosphites  all  of  the  calcium  salt  was  not  decomposed)  an  am- 
moniacal  solution  of  ammonium  citrate  is  added  to  redissolve  the  pre- 
cipitate before  the  addition  of  magnesia  mixture  is  made.    From  the 
