60 
ON  THE  RANCIDITY  OF  FATS. 
specimens,  viz. :  lard  well  stirred,  lard  mixed  with  oil  of  pimen- 
to in  the  proportion  of  two  drops  to  the  ounce,  lard  mixed  with 
oxide  of  mercury  one  drachm  to  the  ounce, — and  placed  them 
where  the  temperature  ranged  between  70°  and  80°. 
On  the  21st  of  April  (ninety  days)  I  first  observed  a  change 
in  the  lards  mixed  with  oxide  of  mercury, — No.  1,  strained  at 
140°,  being  the  least,  and  No.  3,  strained  at  220°  the  most  al- 
tered. The  scented  and  plain  lards,  tested  with  iodide  of  po- 
tassium, all  produced  slight  coloration  after  half  an  hour,  but 
the  scented  lards  less  than  the  plain.  No.  3  appeared  to  better 
advantage  than  the  less  heated  specimens.  After  thirty  hours' 
exposal  on  the  slab  to  light  and  air,  a  most  extraordinary 
change  was  observed.  Nos.  1  and  2  of  the  plain  lards  had  as- 
sumed an  orange  color,  No.  3  a  similar  tint,  but  only  half  as 
dark,  whilst  the  scented  lards  had  lost  rather  than  acquired 
color, — in  fact  produced  an  ointment  at  that  time  perfectly 
saleable.  The  contrast  was  most  striking,  and  continued  so 
for  two  months ;  by  which  time  all  the  specimens  were  of  an 
orange  color,  but  the  scented  lards  only  externally, — probably 
affected  by  the  fumes  of  the  laboratory. 
These  same  lards  were  again  examined  July  7.  Those  mixed 
with  oxide  of  mercury  were  all  hopelessly  bad.  The  rest  were 
tested  with  iodide  of  potassium,  and  after  eight  hours'  exposure 
presented  the  following  appearances : — Nos.  1,  2,  and  3  of  the 
plain  were  of  a  lemon  color,  the  tint  of  No.  1  being  less  than 
that  of  No  2. ;  of  No.  2  less  No.  3.  The  scented  lards  still 
maintained  their  superiority,  Nos.  1  and  3  being  quite  useable, 
No.  2  not  so. 
August  26th,  I  again  examined  them,  with  the  same  results. 
I  therefore  conclude  that  oil  of  pimento,  which,  of  those  that 
had  maintained  the  neutrality  of  oxide  of  mercury  ointment, 
appears  the  best  adapted  for  the  purpose,  is  a  useful,  agreeable 
and  easily  applied  remedy  for  preventing  or  very  much  retard, 
ing  rancification  in  fats  and  fatty  mixtures. 
I  think  I  am  also  justified  in  adding  this  corollary — that  it 
is  advisable  when  preparing  ointments  with  a  view  to  their  pre- 
servation, to  use  ingredients  retaining  unaltered  the  odorous 
principles  with  which  nature  has  for  obvious  purposes  endowed 
them ;  that  is  to  say,  I  would  use  yellow  wax  instead  of  white 
