234  Ointment  of  Mercuric  Nitrate.  {AmMa^"ifo5.arm' 
invariably  accompanied  by  the  concrete  principles  of  oils,  either 
stearin  or  palmitin,  or  both.  A  glance  at  the  empirical  formula  of 
olein  C3H5  (OC18K330)3  at  once  reveals  to  us  the  fact  that  it  is  an 
oleate  of  the  triad  radical  glyceryl,  C3H5. 
By  reaction  with  nitric  acid,  or  more  exactly  speaking,  under  the 
influence  of  nitrous  acid  fumes,  olein  is  converted  into  a  deep  yellow, 
butyraceous  mass.  If  this  be  treated  with  hot  alcohol,  a  deep 
orange-red  oil  is  dissolved,  and  a  peculiar  fatty  matter  remains,  called 
elaidin.  This  is  white,  crystalline,  fusible  at  340  C,  and  appears  to 
be  isomeric  with  olein.  The  solid  fat  then  which  forms  the  base  of 
our  ointment  is  elaidin,  accompanied  by  red  oil.  The  result  of  the 
action  of  nitric  acid  upon  lard  oil,  then,  is  a  mutual  decomposition 
of  the  acid  and  the  fat,  producing  nitrogen  dioxide,  this  becoming 
the  tetroxide,  and  the  transformation  of  triolein  into  its  isomer 
elaidin.  In  the  next  place  the  reaction  is  characterized  by  a  violent 
evolution  of  volatile  products.  These  volatile  products  are1  a 
number  of  the  volatile  fatty  acids  of  the  series  CnH2n02,  from  acetic 
to  capric  inclusive,  together  with  the  dibasic  acids,  adipic  and 
sebacic,  of  the  series  CnH2n.204.  Unquestionably  the  most  desira- 
ble  starting  point  for  the  production  of  elaidin  and  red  oil  is  olein 
of  animal  origin,  and  recognized  in  the  United  States  Pharmacopoeia 
as  lard  oil. 
The  higher-priced  fats  frequently  suffer  adulteration  with  cheaper 
ones,  and  owing  to  the  similarity  of  composition,  such  admixtures 
are  difficult  to  recognize.  The  fact  that  dealers  in  petroleum  oils 
sell  large  quantities  of  lard  oil  has,  no  doubt,  led  many  pharmacists 
to  look  about  for  substitutes  for  lard  oil  in  the  preparation  of  this 
ointment,  presuming  that  lard  oil  would  be  adulterated  to  a  shame- 
ful degree;  but  this  oil,  and  that,  too,  of  excellent  quality,  is  to  be 
had  notwithstanding  that  fact. 
Several  years  ago  I  set  out  to  procure  samples  of  lard  oil  to  be 
used  in  making  citrine  ointment,  since  up  to  this  time,  and  I  be- 
lieve for  twenty-five  years,  this  ointment  had  been  made  with  fresh 
unsalted  butter  by  Dr.  Geo.  Ross  &  Co.  The  very  first  sample, 
upon  critical  examination,  proved  of  excellent  quality  ;  whereupon  I 
procured  a  larger  quantity  of  the  oil.  Lard  oil  is  defined  by  the 
Pharmacopoeia  as  "  A  fixed  oil  expressed  from  lard  at  a  low  tem- 
1  Witthaus,  Manual  of  Chemistry,  p.  266. 
