Am April!  f897arm  }    Note  on  Ointment  of  Mercuric  Nitrate,  211 
stances  have  no  practical  bearing  if  there  be  no  mercuric  salt 
present. 
The  important  practical  point  to  observe  is  that  the  temperature 
be  kept  low  after  the  addition  of  the  mercuric  solution,  when  the 
tendency  to  blacken  increases  as  the  temperature  rises.  This  change 
will  occur  even  if  the  ointment  be  kept  at  ioo°  C.  (21 2°  F.)  for  any- 
thing like  an  hour,  and  possibly  in  much  less  time. 
The  interesting  nature  of  Mr.  Squire's  communication  suggested 
to  the  writer  the  advisability  of  reporting  its  data  to  American 
pharmacists,  and  also  of  making  a  few  practical  suggestions  regard- 
ing the  present  U.S. P.  process. 
The  following  formula  is  suggested  for  trial : 
Grammes. 
Red  mercuric  oxide   75  5 
Nitric  acid  .  „  175- 
Iyard  oil  760* 
Heat  the  lard  oil  in  a  glass  or  porcelain  vessel  to  ioo°  C.  (21 2°  F.), 
withdraw  heat,  and  gradually  add  75  grammes  of  nitric  acid.  When 
the  reaction  moderates,  reapply  the  heat  until  brisk  effervescence 
takes  place,  and  then  withdraw  heat  until  active  effervescence  sub- 
sides. Then  gently  heat  until  effervescence  ceases.  (During  the 
effervescence  stir  the  mixture  with  a  wooden  spatula  or  paddle.) 
Allow  the  mixture  to  cool  to  about  60  0  C.  (1400  F.).  Having  dis- 
solved the  red  oxide  of  mercury  in  100  grammes  of  nitric  acid,  with 
the  aid  of  sufficient  heat,  add  the  solution  gradually  to  the  oxidized 
fat,  and  stir  the  product  until  cold.  When  nearly  cold,  add  50 
grammes  of  glycerin,  and  admix  thoroughly. 
The  advantage  in  using  red  mercuric  oxide  over  mercury  rests  in 
the  fact  that  small  quantities  of  it  are  more  easily  weighed,  and  it  is 
probably  purer  than  commercial  mercury.  If  it  be  desirable  to  employ 
red  mercuric  oxide  for  making  the  official  solution  of  mercuric  nitrate, 
it  should  be  equally  useful  in  making  the  ointment.  The  small 
quantity  of  water  formed  in  the  reaction  is  of  no  practical 
moment. 
In  the  U.S.P.  process,  no  directions  are  given  for  stirring  the 
fatty  mixture  during  oxidation,  and  the  inference  is  that  such  a 
practice  is  to  be  tabooed.  As  a  matter  of  fact,  a  diligent  stirring  of  fat 
and  oxidizing  material  facilitates  oxidation,  and  in  the  writer's  opin- 
ion is  of  decided  advantage  in  hastening  the  end- reaction.    If  the 
