Am.  Jour.  Pharm.  \ 
Jan.  1, 1873.  J 
Chromic  Acid. 
23 
The  subchloride  in  the  other  samples,  although  in  one  instance  it 
amounts  to  as  much  as  6'5  per  cent.,  I  consider  to  be  rather  the  work 
of  careless  manufacture  than  an  adulteration.  It  would  appear  that 
after  the  bismuth  is  dissolved,  the  silver,  which,  as  we  have  seen,  must 
be  frequently  present,  is  precipitated  as  chloride  bj  hydrochloric  acid, 
and  removed  by  decantation.  If  this  is  done  carefully,  there  could 
be  no  objection  to  such  a  process,  but  that  it  is  not  generally  done 
carefully  is  sufficiently  proved  by  the  presence  of  varying  quantities 
of  subchloride,  and  in  seven  samples  out  of  fifteen,  of  chloride  of  sil- 
ver. Samples  7,  9  and  11,  which  are  very  pure,  I  find,  on  inquiry, 
were  manufactured  by  Howards  &  Sons,  Stratford. — Pharm.  Journ. 
and  Trans. ,  Nov.y  16,  1872. 
NEW  METHOD  OF  PREPARING  CHROMIC  ACID  * 
By  E.  Duvillier. 
The  chromate  of  barium  is  decomposed  at  a  boiling  beat,  with  an 
excess  of  nitric  acid.  The  almost  insoluble  nitrate  of  barium  is  pre- 
cipitated in  a  crystalline  form,  and  chromic  acid  remains  in  solution. 
The  latter  is  purified  by  successive  evaporations,  and  by  finally  treat- 
ing with  a  suitable  quantity  of  dilute  sulphuric  acid. 
The  process  is  as  follows  :  Boil  for  ten  minutes  100  parts  chromate 
of  barium,  100  parts  water,  110  parts  nitric  acid,  sp.  gr.  40°  B. 
The  water  should  first  be  poured  on  the  chromate  of  barium  to  form 
a  kind  of  magma,  and  the  nitric  acid  added  afterward.  This  is  im- 
portant, because,  if  the  opposite  order  is  followed,  the  result  is  not 
as  good,  and  the  nitrate  of  barium  formed  incloses  in  it  chromate  of 
barium. 
To  the  red  liquor  add  200  parts  of  water,  and  allow  it  to  boil  for 
ten  minutes.    The  nitrate  of  barium  settles  rapidly  when  left  quiet. 
The  supernatant  liquid,  when  cold,  contains  4  parts  of  nitrate  of 
barium  to  100  of  soluble  substances.  This  is  decanted  and  evaporated 
to  nearly  the  volume  of  the  acid  used.  During  this  operation  the 
greater  part  of  the  dissolved  nitrate  of  barium  is  precipitated,  and 
when  the  liquid  cools  chromic  acid  is  obtained,  containing  only  0'5  per 
cent,  of  nitrate  of  barium. 
The  excess  of  nitric  acid  is  expelled  by  evaporating  nearly  to  dry- 
*  Translated  for  the  Journal  of  Applied  Chemistry  from  Dingler's  Polytech- 
nisches  Journal. 
