V 
Am"  Dec  "'iS5arm' }  Tests  for  Hypophosphites.  609 
TESTS  FOR  HYPOPHOSPHITES. 
By  Frank  X.  Moerk,  Ph.G. 
Contribution  from  the  Chemical  Laboratory  of  the  Philadelphia  College  of  Pharmacy. — 
No.  81. 
As  stated  in  an  article  upon  "  The  Estimation  of  Hypophosphorous 
Acid  and  the  Hypophosphites,"1  there  are  three  tests  obtainable 
with  this  acid  and  its  salts,  which  are  said  to  be  characteristic:  (1) 
The  cuprous  hydride  precipitate  changing  upon  boiling  into  metallic 
copper  and  hydrogen,  this  test  answering  only  in  comparatively 
concentrated  solutions ;  (2)  the  blue  color  or  precipitate  with  acid 
solution  of  ammonium  molybdate  after  the  addition  of  a  few  drops 
of  sulphurous  acid ;  (3)  the  blue  color  with  tungstates  under  the 
same  conditions.  The  last  two  tests  are  obtainable  in  dilute  solu- 
tions. The  molybdate  test,  according  to  E.  J.  Millard,2  is  best 
applied  as  follows :  "  To  a  solution  of  hypophosphorous  acid  or  any 
of  the  hypophosphites  the  acid  solution  of  ammonium  molybdate  is 
added,  and  then  a  few  drops  of  sulphurous  acid  ;  a  blue  precipitate 
is  immediately  formed,  or,  if  the  solution  be  dilute,  a  blue  coloration 
is  produced  which  is  considerably  intensified  by  agitation  or  gentle 
warming."  Millard  further  states  that  H2S  and  SnCl2,  as  reducing 
agents,  do  not  give  the  reaction  because  they  carry  the  reduction 
too  far,  namely,  to  the  brown  state.  Of  salts  interfering  with  the 
reaction,  he  says :  Chlorates  prevent  it,  sulphides  produce  a  brownish- 
black  precipitate  that  would  completely  hide  it,  and  thiosulphates 
reduce  the  molybdate  to  the  brown  state. 
For  several  years  prior  to  the  publication  of  the  above,  it  was 
noticed  in  the  Chemical  Laboratory  of  the  College  that  students 
occasionally  obtained  a  blue  color  with  ammonium  molybdate  in  a 
solution  containing  thiosulphate ;  although  I  often  made  the  test 
with  the  same  solutions  and  occasionally  obtained  the  blue  color ; 
still  the  number  of  times  I  was  successful  in  this  bears  a  very  small 
ratio  to  the  number  of  times  I  was  unsuccessful,  even  though  the 
reagents  were  added  in  the  same  quantities  and  in  the  same  order. 
After  a  large  number  of  experiments,  the  difficulty  in  always 
obtaining  the  blue  color  was  found  to  be  due  to  the  excess  of  nitric 
acid  present  in  the  solution  of  ammonium  molybdate  ;  for  if  the 
Am.  Jour.  Pharm.,  1889,  326. 
Pharm.  Journal,  Jan.  26,  1889.  Reprinted  in  Am.  Journ.  Pharm.,  1889,  129. 
