AmDecuy■lSarm•}   *         Tests  for  Hypophosphites.  611 
molybdate.  It  was  found  that  thiosulphate  and  sulphite  alone  give 
no  blue  color,  and  stannous  chloride  produces  only  a  greenish  color 
or  precipitate.  Hence,  of  the  two  tests,  this  one  appears  to  be  the 
most  characteristic  of  hypophosphites.  To  obtain  this  test  the  solu- 
tion of  sodium  tungstate  in  distilled  water  (I  :  100)  is  acidified  (rather 
strongly)  with  nitric  acid,  then  the  hypophosphite  and  sulphite 
solutions  added  and  moderately  warmed ;  the  blue  color  resembles 
that  of  Fehling's  solution  and  more  rapidly  intensifies  than  the  cor- 
responding test  with  molybdate.  Experiments  made  to  ascertain 
how  delicate  these  two  tests  were  proved  that  solutions  containing 
one  part  calcium  hypophosphite  in  5,000  parts  of  water  still  gave 
very  distinct  blue  colorations ;  in  this  dilution  the  molybdate  test  is 
frequently  obtained  of  a  greenish-blue  color,  while  the  tungstate  is 
a  very  fine  blue ;  solutions  containing  one  part  in  10,000  parts  of 
water  failed  to  respond.  Millard  does  not  find  the  molybdate  test 
quite  as  delicate,  he  stating  that  one  part  in  2,000  can  still  be 
detected ;  in  mixtures  he  finds  I  in  300  to  be  the  limit. 
Experiments  were  next  made  to  ascertain  if  it  was  possible  to 
detect  with  both  the  molybdate  and  the  tungstate  tests  the  hypo- 
phosphite in  presence  of  the  interfering  salts,  sulphides,  thiosulphates 
and  chlorates.  Solutions  containing  one  per  cent,  of  these  salts 
were  mixed  with  equal  volumes  of  a  solution  containing  o-i  per 
cent,  of  calcium  hypophosphite,  so  the  solution  contained  hypophos- 
phite I  :  2000 and  10  :  2000  of  the  other  salts.  The  chlorate  prevented 
not  only  the  molybdate  but  also  the  tungstate  test  for  the  hypophos- 
phite (even  in  solutions  containing  one  per  cent,  each  of  'chlorate 
and  hypophosphite)  ;as  previously  stated,  by  boiling  such  a  solution 
with  hydrochloric  acid,  the  hypophosphite  is  completely  and  rapidly 
converted  into  phosphate.  After  numerous  experiments,  the  follow- 
ing procedure  allowed  the  detection  of  the  hypophosphite :  To  the 
mixture  of  chlorate  and  hypophosphite  an  equal  volume  of  one  per 
cent,  sodium  tungstate  solution  is  added,  then  a  crystal  of  sodium 
sulphite  and  nitric  acid  to  acid  reaction  (should  the  odor  of  S02  dis- 
appear, another  crystal  of  Na2SOs  must  be  added);  on  slight  warm- 
ing the  blue  color  develops ;  the  blue  color  is  as  fine  as  though 
obtained  from  a  pure  hypophosphite  solution.  This  test  is  probably 
successful  because  the  liberated  chloric  acid  or  its  decomposition  pro- 
duct oxidizes  first  the  S02  without  acting  upon  the  hypophosphite 
and,  hence,  the  caution  that  the  odor  of  S02  must  be  apparent 
before  warming. 
