AmMa°rUch.Sym'}     Molybdate  Test  for  Hypophosphites.  129 
NOTE  ON  THE  MOLYBDATE  TEST  FOR  HYPOPHOS- 
PHITES.1 
By  E.  J.  Millaed,  Pharmaceutical  Chemist. 
In  several  text-books  of  pharmaceutical  chemistry,  and  also  in  the 
National  Dispensatory  by  Stille  and  Maisch,  amnionic  molybdate  is 
stated  to  give  a  blue  precipitate  with  hypophosphorons  acid  and  the 
hypophosphites.  No  details  of  the  reaction  are  given,  although  it  is 
recommended  as  a  test. 
As  far  as  I  have  been  able  to  ascertain,  the  test  is  founded  on  the 
observations  of  "Winkler,2  at  least  he  is  the  earliest  authority  on  the 
subject,  for  in  1850  he  mentions  that  hypophosphites  are  colored  blue 
by  molybdate  of  ammonium,  and  that  a  mixture  of  phosphate  with 
hypophosphite  yields  a  green  coloration,  owing  to  the  combination  of 
yellow  phosphomolybdate  with  the  blue. 
Now,  in  common  with  many  others,  I  have  never  been  able  to  get 
a  blue  precipitate,  when  solutions  of  the  two  bodies  are  mixed,  and 
only  a  faint  coloration  appears  after  standing  some  considerable  time, 
nor  does  the  fact  of  the  solution  of  the  molybdate  being  acid,  neutral 
ol'  alkaline,  make  any  difference  in  this  result. 
Whilst  experimenting  with  solutions  of  amnionic  molybdate  and 
hypophosphites,  I  noticed  that  the  addition  of  a  small  quantity  of  sul- 
phurous acid  rendered  the  inoperative  test  a  most  delicate  one.  More- 
over, the  ordinary  nitric  acid  solution  of  molybdate  of  ammonium, 
used  as  a  test  for  phosphoric  acid,  answers  even  better  than  a  neutral 
or  alkaline  solution.  For,  if  to  a  solution  of  hypophosphorous  acid 
or  any  of  the  hypophosphites  the  acid  solution  of  ammonic  molybdate 
be  added,  and  then  a  few  drops  of  sulphurous  acid,  a  blue  precipitate  is 
immediately  formed,  or  if  the  solution  be  dilute,  a  blue  colorationis  pro- 
duced which  is  considerably  intensified  by  agitation  or  gentle  warming. 
Phosphoric  acid  and  the  phosphates,  phosphorous  acid  and  the  phos- 
phites similarly  treated  do  not  react,  neither  do  pyrophosphates. 
The  reaction  is,  I  believe,  due  to  the  partial  reduction  of  Mo03  to 
Mo3Os  by  the  hypophosphorous  acid,  which  is  completed  by  the  sul- 
phurous acid.  This  blue  oxide  has  been  shown  by  Pfordten3  to  exist 
between  colorless  Mo03  and  brownish  Mo02. 
1  Reprint  from  the  Phakmaceutical  Journal,  Jan.  26,  1889  :  communicated 
by  the  author. 
2  PoggendorfFs  "  Annalen  d.  Physik  u.  Chemie,"  Band  cxi.,  p.  443. 
3  Joum.  Chem.  Soc,  Abstracts,  1884,  page  559. 
