ON  THE  RANCIDITY  OF  FATS. 
57 
Shortly  after  the  use  of  benzoinated  lard  had  been  recom- 
mended for  the  preparation  of  zinc  ointment,  which  it  is  well 
known  to  preserve  against  rancification,  I  applied  with  success 
the  same  idea  to  other  ointments  of  similar  composition,  viz. : 
those  containing  metallic  oxides,  whose  presence  had  been 
found  to  act  unfavorably  on  the  keeping  qualities  of  the  fats 
with  which  they  were  associated.  These  were  calamine  cerate 
and  oxide  of  mercury  ointment.  I  have  found  that  M.  De- 
schamps,  in  1843,  recommended  the  same  proceedings  in  making 
oxide  of  mercury  ointment,  and  also  the  ointments  of  iodide  of 
potassium  and  acetate  of  lead.  For  ointment  of  tutty  and  blue 
ointment,  where  a  little  extra  color  would  not  be  objectionable, 
he  directs  the  use  of  "  graisse  populinee,  the  keeping  qualities 
of  which  are  really  extraordinary.  M.  Deschamps  states  that 
whilst  the  "graisse  benzinee  "  will  keep  good  for  one  year,  the 
''graisse  populinee"  will  keep  good  for  an  unlimited  time.  He 
suggests  its  use  for  greasing  machinery  even.  I  intended  to 
make  some  of  this  preparation,  but  could  not  get  the  poplar  buds. 
The  French  perfumers,  in  preparing  the  base  of  their  pomades, 
adopt  a  process  somewhat  similar,  viz.,  digestion  with  benzoin 
after  a  preliminary  washing,  and  boiling  with  solution  of  salt 
and  alum.  Their  method  yields  a  stable  fat,  but  it  is  too 
troublesome  to  be  be  frequently  performed,  and  succeeds  best 
on  the  large  scale, — consequently  is  not  well  adapted  for  the 
pharmaceutist. 
For  experiment  on  the  nature  of  the  preservative  power  exer- 
cised on  fats  by  bodies  like  benzoin,  the  oxide  of  mercury  oint- 
ment was  evidently  well  adapted,  as  the  progress  of  rancifica- 
tion is  marked  by  alteration  of  color — the  oxide  being  reduced 
pari  passu  with  the  oxidation  of  the  fat. 
It  was  my  impression  that  the  essential  oil  had  more  to  do  in 
the  matter  than  any  other  constituent  of  the  gum,  though  it  had 
been  asserted  that  benzoic  acid  answered  equally  well.  But 
the  acid  of  commerce  contains  ah  abundance  of  the  odorous 
principle. 
To  test  the  truth  of  the  surmise,  and  at  the  same  time  ascer- 
tain what  degree  of  effect,  if  any,  was  produced  by  various  es- 
sential oils,  I  prepared,  on  December  5th,  1861,  a  quantity  of 
red  precipitate  ointment,  using  ordinary  lard  and  wax  in  the 
