332  Estimation  of  Hypophosphites.        {Am j^£arm- 
phites  corresponding  to  1  cc.  NaOH,  the  quantity  of  hypophosphite 
will  be  obtained  : 
For  Ca(H2P02)2  multiply  by  0  014166 
"  NaH2P02  "  "  0-014666 
"   KH2P02  "         "  0-016850 
"    Fe2(H2P02)6       "         "  0-013940 
The  sodium  hydrate  solution  must  be  accurately  standardized  as  a 
slight  error  will  make  a  considerable  difference  if  expressed  as  per- 
centage of  hypophosphite. 
The  addition  of  the  calcium  chloride  is  made  to  correctly  indicate 
the  reaction  of  the  solution ;  phosphoric  acid  titrated  with  sodium 
hydrate  solution  will  indicate  an  alkaline  reaction  before  all  of  it  has 
been  changed  into  Na2HP04,  although  this  is  an  acid  salt ;  by 
the  addition  of  CaCl2  there  is  formed  the  acid  salt,  CaHP<34, 
which  has  an  acid  reaction,  and  which  by  addition  of  NaOH  is 
changed  into  the  normal  calcium  phosphate  with  neutral  reaction. 
This  method  must  only  be  applied  in  neutral  solutions ;  should  the 
hypophosphite  have  an  acid  or  alkaline  reaction,  the  amount  of  acid 
or  alkali  required  to  neutralize  must  be  ascertained  and  allowed  for  in 
the  above  method.  For  this  reason  hypophosphorous  acid  was  not 
placed  in  the  above  list ;  its  estimation  is  easily  effected  by  subtracting 
the  number  of  cc.  of  NaOH  required  for  neutralization  of  the  acid  from 
the  total  number  of  cc.  of  NaOH  required  after  oxidation  with  bromine 
and  multiplying  the  remaining  number  of  cc.  of  NaOH  by  0*011. 
The  change  of  a  pure  hypophosphite  into  a  phosphite  must  be  at- 
tended by  the  production  of  an  acid  reaction  for  the  reason  that 
H3P02  is  a  monobasic  acid  while  the  product  of  oxidation,  H3P03,  is 
a  diabasic  acid,  hence,  a  pure  hypophosphite  will  not  be  able  to  neu- 
tralize the  additional  acidity.  In  the  examination  of  hypophos- 
phorous acid,  the  neutralization  figures  play  an  important  part. 
After  using  the  various  methods  it  is  but  proper  to  recommend  the 
one  found  to  be  the  best ;  this  is  undoubtedly  the  volumetric  method 
after  oxidation  with  bromine,  for  as  accurate  results  as  with  the  mer- 
curic chloride  method  are  obtained  in  one-fourth  of  the  time.  For  a 
method  to  be  carried  out  in  a  retail  store,  possibly  the  mercuric  chloride 
would  answer  better  as  there  are  no  objectionable  vapors  generated. 
In  the  examination  of  the  hypophosphorous  acids  and  the  hypo- 
phosphites  probably  more  determinations  were  made  with  the  mer- 
curic chloride  method,  owing  to  the  fact  that  most  of  the  work  had 
been  done  before  the  value  of  the  volumetric  method  was  recognized. 
