AmjSyy'i8P89arm'}        Estimation  of  Hypophosphites.  331 
weight  of  the  magnesium  pyrophosphate  the  hypophosphite  can  be 
calculated  by  use  of  the  factors  : 
For  H3P02  multiply  by  0'5946 
"  NaH2P02  "  "  07928 
"  KH2P02  "  "  0-9378 
"  Ca(H2P02)2  "  "  0-7658 
"    Fe2(H2P02)6    «      «  0-7534 
It  is  to  be  understood  that  if  the  salt  examined  contains  phosphoric 
acid  or  phosphate  this  must  be  determined,  and  the  amount  of  mag- 
nesium pyrophosphate  due  to  it  subtracted  from  the  total  magnesium 
pyrophosphate  before  the  above  calculations  are  made. 
In  writing  out  the  reactions  for  the  oxidation  of  hypophosphites 
and  phosphites  by  means  of  bromine,  it  was  noticed  that  by  neutraliz- 
ing with  sodium  hydrate,  results  identical  with  those  from  the  reduc- 
tion method  with  mercuric  chloride  were  to  be  obtained. 
NaH2P02+(Br2)2+2H20=]SraH2P04+4HBr 
2Na2HP03-f-(Br2)2+2H20=2Na2HP04+4HBr. 
Both  reactions  yield  products  which  will  require  for  neutralization 
six  molecules  sodium  hydrate ;  and,  as  in  the  case  of  the  mercuric 
chloride  method,  two  molecules  phosphite  will  be  calculated  as  one 
molecule  hypophosphite.  Should  phosphite  be  present  the  hypophos- 
phite deduced  from  the  phosphoric  acid  determination  will  exceed 
that  found  by  this  volumetric  method,  the  excess  representing  one 
molecule  hypophosphite  derived  from  two  molecules  phosphite. 
This  method  will  allow  of  a  rapid  determination  of  the  reducing 
value  and  at  the  same  time  prepare  the  solution  for  the  phosphoric 
acid  estimation,  thus  combining  the  essential  points  in  the  analysis  of 
the  hypophosphites.  The  determination  is  effected  as  follows  :  0*2  to 
0.3  gm.  of  the  hypophosphite  are  mixed  with  100  cc.  water  in  a  covered 
beaker  and  bromine  added,  a  few  drops  at  a  time,  until  the  color  no 
longer  disappears  even  after  application  of  a  moderate  heat ;  the  ex- 
cess of  bromine  is  removed  by  boiling  the  solution  until  free  from 
color  (no  fear  need  be  entertained  of  a  loss  of  acid  as  a  very  dilute  acid 
solution,  such  as  this,  loses  upon  boiling  only  water  until  the  acid  be- 
comes so  concentrated  as  to  contain  47  per  cent.  HBr),  15  cc.  of  a 
neutral  10  per  cent,  calcium  chloride  solution  and  a  few  drops  of  phe- 
nolphthalein  solution  added  and  then  titrated  with  normal  sodium 
hydrate.  By  multiplying  the  number  of  cc.  of  NaOH  required  by 
the  following  factors,  which  represent  the  quantities  of  hypophos- 
