418 
OINTMENT  OF  MERCURIC  NITRATE. 
When  these  mercurial  solutions  come  in  contact  with  the  heated 
glycerides,  the  complicated  reaction  which  immediately  ensues 
commences  with  two  distinct  phases.  One  of  these  is  charac- 
teristic only  for  the  so-called  non-drying  oils  ;  the  other  is  pretty 
general  with  all.  The  first  of  these  is  determined  by  the  cata- 
lytic action  of  the  nitrogen  tetroxide  (which  is  always  present  in 
the  mercurial  solution  prepared  without  heat,  and  should  it  not 
be  present,  as  would  be  the  case  by  employing  a  solution  con- 
taining the  mercuric  nitrate  only,  it  wouM  of  course  simulta- 
neously result  from  the  mutual  decomposition  of  the  nitric  acid 
and  the  fats),  and  consists  in  the  transformation  of  the  liquid 
triolein  into  its  white  concrete  and  crystalline  isomere  elaidin. 
But  the  second,  which  is  characterized  by  the  violent  evolution 
of  volatile  products,  consists,  according  to  the  prolongation  of 
the  reaction  or  its  intensity,  favored  by  external  causes,  and  the 
relative  quantity  of  nitric  acid,  of  the  destruction  of  part  of  the 
oleic,  palmitic  and  stearic  acid  contained  in  the  glycerides  that 
are  usually  employed. 
But  the  complete  dissociation  of  the  original  compounds  is 
effected  with  difficulty.  Pure  lard,  heated  with  8  and  10  times 
the  quantity  of  strong  nitric  acid  until  the  latter  w"as  dissipated, 
still  was  attacked  by  a  fresh  portion.  In  this  case,  all  of  the  9 
volatile  acids  of  the  series  GJl^'fi-z^  from  acetic  to  capric  inclu- 
sive, are  produced  together  with  fixed  acids  of  the  series  GJI^^ — - 
2O4,  of  which  suberic  and  succinic  acid  are  more  abundantly  pro- 
duced from  glycerides  containing  chiefly  palmitin.  A  peculiar 
and  undetermined  substance  is  invariably  generated  in  quantity, 
and  resists  the  destructive  action  of  the  nitric  acid  with  remark- 
able obstinacy.  This  is  an  intensely  yellow  oil,  which  saponifies 
with  potassium  hydrate,  with  the  formation  of  a  deep  red  color; 
and  it  is  this  compound  to  which  the  ointment  of  mercurial  ni- 
trate owes  its  yellow  color.  It  is  supposed  that  the  discoloration 
of  the  officinal  ointment  occurs  more  particularly  when  the 
oxidation  of  the  fatty  matter  has  not  been  sufficient,  and  that 
subsequently  the  avidity  of  these  bodies  robs  the  mercurial  salts 
of  their  oxygen  and  reduces  them  to  the  metallic  state  ;  but  in 
the  officinal  ointment  the  greater  part  of  the  mercury  no  longer 
exists  as  normal  nitrate,  but  chiefly  as  basic  nitrate  and  raer- 
