420 
OINTMENT  OF  MERCURIC  NITRATE. 
substances,  even  in  the  presence  of  a  large  excess  of  free  nitric 
acid,  which  seems  to  indicate,  in  this  instance  at  least,  that  the 
replacement  of  the  hydrogen  atom  of  the  acid  molecule  through 
the  mercurial  atom  renders  it  more  unstable  in  the  presence  of 
organic  matter,  and  therefore  a  more  powerful  oxidizer. 
The  evolution  of  nitrogen  dioxide  during  the  solution  of  the 
resinous  remnant  insoluble  in  chloroform  would  also  indicate 
that  the  body  contained  either  metallic  mercury  or  the  suboxide. 
This  supports  the  supposition  that  the  mercurous  compounds  are 
less  stable  than  the  mercuric  under  similar  circumstances.  It 
also  affords  incontrovertible  evidence  that  in  the  officinal  oint- 
ment the  smallest  portion  of  the  mercury  exists  as  nitrate,  and 
that  the  greater  portion  can  be  present  in  an  indefinite  variety 
of  forms.  Therefore,  the  only  form  in  which  the  metal  should 
be  combined  is  as  mercuric  nitrate,  and  the  title  should  designate 
it  accordingly. 
Secondly — A  portion  of  the  fatty  substance  which  the  formula 
demands  cannot  be  obtained  unless  the  pharmaceutist  prepares 
it  himself,  because  an  officinal  neat's  foot  oil  does  not  exist  in 
the  market,  but  a  rank  and  disgusting  semi-fluid  grease,  which 
possesses  none  of  the  officinal  characteristics.  But  pure  lard 
can  always  be  readily  obtained,  and,  since  it  furnishes  an  ex- 
cellent ointment,  should  invariably  be  used. 
Thirdly — The  manner  of  executing  the  officinal  operation  is 
the  very  embodiment  of  failure.  In  this  process  it  is  of  the 
utmost  necessity  to  employ  vessels  of  immense  proportionate 
size.  It  is  a  point  of  great  importance  to  retain  the  tempera- 
ture of  the  heated  fats  within  certain  limits,  which  is  an  exceed- 
ingly difficult  office  to  perform  after  a  violent  reaction  has  set 
in  ;  and  even  with  all  these  precautions  the  ointment  may  over- 
flow or  its  color  be  impaired  from  reduction  of  the  metal  by  too 
great  a  heat.  The  production  of  a  good  ointment  by  this  pro- 
cess is,  therefore,  a  matter  of  chance,  and  depends  upon  circum- 
stances that  seem  rather  the  good  luck  of  the  operator  than  a 
well-defined  pharmaceutical  process. 
Now  all  these  difficulties  can  be  readily  overcome  by  an 
entire  change  in  the  operation  itself,  regardless  of  the  compo- 
.nent  elements  of  the  formula.    The  new  process  rests  upon  a 
