OINTMENT  OF  MERCURIC  NITRATE. 
421 
scientific  basis  whose  characteristic  feature  pervades  it  in  every 
detail,  and  which  must  therefore  invariably  yield  a  uniform  and 
definite  result.  Two  parallel  operations,  separate  and  distinct, 
unite  their  perfect  results  to  one  complete  and  unchangeable 
whole.  The  formation  of  mercuric  nitrate  is  effected  with  the 
requisite  quantity  of  nitric  acid,  and  the  remainder  is  completely 
consumed  in  the  oxidation  of  the  fats.  This  insures  the  ultimate 
existence  of  but  one  compound  of  mercury  in  the  finished  pro- 
duct, and  that  is,  as  the  title  implies,  the  mercuric  nitrate.  It 
likewise  admits  of  the  oxidation  of  the  fatty  matter  to  the  utmost 
capacity  of  all  the  available  nitric  acid,  so  that  when  the  last 
vestige  of  this  has  disappeared  the  mercurial  solution  can  be 
mixed  with  the  nearly-cooled  product  without  causing  any  far- 
ther reaction.  A  very  decided  advantage  of  this  process  is  that 
the  enormously  large  vessels  can  be  dispensed  with.  The  nitric 
acid  is  added  to  the  melted  fat,  and  the  heat  continued  until 
brisk  ebullition  sets  in.  This  occurs  mainly  in  the  centre  of  the 
mixture,  and  without  frothing.  It  is,  however,  of  the  utmost 
necessity  not  to  disturb  the  liquids  by  stirring.  If  the  reaction 
becomes  too  violent,  the  mixture  must  be  removed  a  short  time 
from  the  fire ;  and  if  the  action  slackens  too  much,  it  must  be 
replaced.  Finally,  when  all  the  nitric  acid  has  been  decomposed, 
the  temperature  can  be  considerably  raised  without  causing  any 
farther  effervescence.  The  boiling  then  is  analogous  to  the 
boiling  of  fatty  matters  in  general. 
From  the  foregoing  results  the  following  formula  is  deduced  : 
Take  of  Mercury    .        .        .       •    li  troyounces. 
Nitric  Acid,  sp.  gr.  1-42,   .    SJ  " 
Lard  (pure)       .        .        .  16J  " 
Dissolve  the  mercury  in  900  grains  of  the  nitric  acid,  with  the 
aid  of  heat,  and  keep  the  solution  gently  warm  to  prevent  crys- 
tallization before  it  is  used.    Melt  the  lard  in  a  suitable  vessel, 
with  a  moderate  heat ;  then  add  the  remainder  of  the  nitric  acid, 
and  continue  the  heat,  without  stirring  the  mixture,  as  long  as 
moderate  effervescence  continues  ;  but  if  this  becomes  too  violent, 
remove  the  mixture  from  the  fire,  and  only  replace  it  when  the 
action  slackens  too  much.    Finally,  when  effervescence  ceases 
and  the  liquid  only  boils  even  under  an  increased  heat,  remove 
