AmoZ*x87h8arm'}      Blue  Solution  of  Molybdic  Acid.  493 
THE  BLUE  SOLUTION  OF  MOLYBDIC  ACID  AS  A 
REAGENT. 
By  O.  Maschke. 
If  calcium  molybdate  is  moistened  with  a  quantity  of  dilute  hydro- 
chloric acid  sufficient  to  produce  a  clear  solution  on  the  application  of 
a  gentle  heat,  a  deep  blue  coloration  quickly  appears  in  the  liquid.  In 
place  of  calcium  molybdate  those  of  ammonium,  sodium  or  potassium 
may  be  used,  adding  so  much  hydrochloric  acid  that  the  liquid  if  poured 
upon  a  plate  of  polished  marble  may  produce  a  visible  but  very  slight 
effervescence.  If  after  cooling  a  concentrated  solution  of  sodium  or 
calcium  chloride  is  poured  into  the  liquid  there  is  formed  a  blue-black 
precipitate,  not  easily  distinguished  in  the  liquid,  and  which  may  be 
regarded  as  a  compound  of  molybdic  acid  and  molybdic  oxide.  It  dis- 
solves with  great  ease,  not  merely  in  water  but  also  in  alcohol,  and 
produces  a  coloration  of  extraordinary  intensity.  The  author  prepares 
the  solution  as  follows:  3  grams  calcium  molybdate,  250  cc.  of  water, 
and  enough  of  hydrochloric  acid  to  effect  the  solution  of  2  grams  of 
cane-  or  grape-sugar.  When  the  deep  blue  coloration  is  apparent  the 
ebullition  is  continued  for  five  minutes.  When  the  precipitate  has 
been  produced  with  sodium  or  calcium  chloride,  it  is  washed  upon  the 
filter  first  with  the  precipitant  and  then  with  a  little  water.  As  soon  as 
the  liquid  begins  to  run  through  of  a  deep  blue  color,  the  filter  with 
its  contents  is  placed  in  distilled  water  and  the  solution  finally  made  up 
to  250  cc.  This  blue  solution  is  decolorized  with  extreme  ease  by 
caustic  alkalies  and  oxidizing  agents,  such  as  chlorine,  nitrous  acid, 
hydrogen  peroxide  and  permanganic  acid.  Hydrochloric  acid  of  spec, 
grav.  1*24  produces  in  this  solution  a  blue  precipitate,  the' supernatant 
liquid  being  colorless.  Sulphuric  acid  of  spec.  grav.  1*840  does  not 
give  a  precipitate,  but  the  color  of  the  liquid  is  altered.  Nitric  acid  of 
spec.  grav.  1*185  produces  a  rapid  decoloration.  Dilute  solutions  of 
ferric  salts  decolorize,  and  those  of  ferrous  salts  occasion  turbidity. 
The  author  has  endeavored  to  employ  the  blue  solution  to  detect  nitrous 
acid  in  spring  waters.  The  water  under  examination  is  mixed  with  a 
little  caustic  soda  ;  after  filtration,  so  much  acetic  acid  is  added  that 
the  liquid  may  have  but  a  very  feeble  acid  reaction.  A  test-tube  is 
three-fourths  filled  with  this  liquid  and  about  6  to  10  drops  of  dilute 
acetic  acid  and  1  to  2  drops  of  the  blue  molybdic  solution  are  added, 
so  that,  in  placing  the  tube  upon  a  white  surface  and  viewing  it  longi- 
