210  Note  on  Ointment  of  Mercuric  Nitrate.  {^l^Xm™' 
speedy  absorption  is  such  that  many  physicians  dilute  the  ointment 
with  fatty  diluents  in  all  cases,  save  th*ose  requiring  strong  stimula- 
tion. Whether  the  elaidin  of  the  ointment  is  of  any  value  in  pro- 
moting absorption  or  not  has  not  been  determined. 
Not  alone  from  the  medical  standpoint,  however,  has  the  ointment 
been  of  interest,  but  its  making  has  been  the  fruitful  source  of  much 
study  by  pharmacists.  Under  the  title  of  "  Unguentum  Hydrargyri 
Nitratis,"  an  able  paper  by  P.  W.  Squire,  has  been  published  in  the 
Pharmaceutical  Journal  of  London  (February  27,  1897,  172),  in 
which  are  given  the  results  of  experiments  upon  the  nature  of  the 
fat,  the  relative  quantity  of  nitric  acid,  and  the  manipulation  used 
in  making  the  ointment.  Especial  attention  is  paid  to  the  differ- 
ences between  the  processes  of  the  British  and  United  States  Phar- 
macopoeias. It  is  not  necessary  to  here  dwell  upon  these,  save  only 
in  a  general  way. 
Regarding  the  fat  to  be  used,  Mr.  Squire  prefers  the  British 
Pharmacopoeia  mixture  of  lard  and  olive  oil,  rather  than  the  lard  oil 
of  the  United  States  Pharmacopoeia.  He  says  that  with  lard  oil  the 
oxidation  takes  place  at  a  lower  temperature  than  with  lard  and 
olive  oil,  the  resulting  product  being  somewhat  darker;  otherwise, 
he  frankly  adds,  there  is  not  much  to  choose  between  the  two  fatty 
bases. 
The  relative  quantity  of  nitric  acid  used  in  the  B.P.  process  is 
considerably  more  than  in  the  U.S. P.,  and  while  the  U.S.P.  treats  the 
lard  oil  with  a  part  of  the  nitric  acid  previous  to  the  addition  of  the 
solution  of  mercuric  nitrate,  the  B.P.  directs  that  the  acid  solution  of 
mercuric  nitrate  be  added  to  the  ointment  base  without  any  previous 
treatment  with  acid.  The  advantage  of  the  first  procedure  over  the 
sceond  Mr.  Squire  admits,  giving  an  alternative  formula  based  on  the 
B.P.  formula,  in  which  the  fatty  base  is  treated  with  half  the  nitric 
acid  before  the  mercurial  solution  is  added. 
Mr.  Squire  finds  that  the  temperature  at  which  effervesence  takes 
place  varies  with  the  nature  of  the  mixture  of  acid  and  fat.  With 
nitric  acid  and  lard  oil  the  reaction  is  slight  at  ioo°  C.  (21 2°  F.)  and 
brisk  at  no0  C.  (2300  F.)  ;  with  nitric  acid,  lard  and  olive  oil,  the 
reaction  takes  place  at  1200  C.  (248 0  F.) ;  with  acid  solution  of 
mercuric  nitrate  and  lard  oil  it  occurs  at  about  900  C.  (1940  F.),  and 
with  acid  solution  of  mercuric  nitrate,  lard  and  olive  oil,  at95°  C. 
(203 0  F.).    The  relatively  higher  temperatures  of  the  first  two  in- 
