526  Ointment  of  Mercuric  Nitrate.  {^s^Sm^xm.' 
phor1 ;  still  others  have  given  their  attention  to  the  mercurial 
portion  of  the  ointment,  and  suggest  making  the  nitrate  from  the 
oxide  of  mercury  instead  of  making  it  from  the  metal.2  Some  have 
even  been  skeptical  as  to  the  reliability  of  any  process3,  but  those 
who  have  approximated  the  truth  more  nearly  are  they  who  advise 
careful  manipulation,  especially  as  regards  temperature.4 
In  regard  to  the  selection  of  Lard  Oil  as  the  official  base  for  the 
ointment,  experiments  have  proven5  that  it  is  superior  to  all  other 
oils  suggested,  consequently  the  fault  does  not  lie  there.  The  chief 
difficulty  appears  to  lie  in  disregarding  the  temperatures  to  be 
observed  during  the  operation. 
It  is  to  be  regretted  that  so  many  good  pharmacists  neglect  the 
use  of  a  thermometer  in  the  manufacture  of  those  preparations  of 
the  Pharmacopoeia  which  require  the  use  of  this  valuable  instru- 
ment. 
The  temperatures  which  are  advised  in  the  working  formulae  of 
many  of  the  official  preparations  have  been  found  by  actual  expe- 
rience to  give  the  most  satisfactory  results  in  practice,  yet  many 
pharmacists  neglect  this  important  feature,  and  then  complain  about 
the  formulae  in  the  U.  S.  P. 
However,  in  the  case  of  Citrine  Ointment,  the  official  process 
does  not  give  uniform  results  even  with  careful  manipulation.  The 
reactions  appear  to  be  satisfactory,  but  the  finished  preparation  is 
generally  found  to  be  spongy  or  granular.  This  is  especially  the 
case  when  working  with  large  quantities,  and  constitutes  a  very 
serious  annoyance. 
While  experimenting  to  overcome  this  difficulty  a  process  was 
found  which  gives  excellent  results  with  either  large  or  small  quan- 
tities, and  it  has  been  used  for  some  time  with  satisfactory  results. 
The  official  ingredients  and  quantities  are  used,  and  the  following 
instructions  regarding  temperatures  must  be  carefully  adhered  to 
First,  heat  the  lard  oil  to  ioo°  C,  as  in  the  official  process,  remove 
heat,  add  the  nitric  acid  without  stirring,  and  reapply  heat  when  effer- 
vescence ceases,  till  all  gas  is  expelled.    It  is  best  to  use  a  vessel  of 
jAm.  Jour.  Phar.  14,  p.  no;  54,  pp.  145-232. 
2Ibid.  58,  p.  8  ;  34,  p.  394. 
3Ibid.  37>  p.  296. 
4Ibid.  4,  p.  197  ;  14,  p.  61  ;  33,  p.  119;  32,  p.  272  ;  41,  p.  21  r. 
5Ibid.  55,  p.  438. 
