*  ■  . 
214  UNaUENTUM  HYDRARaYRI  NITRATIS. 
when  the  temperature  reaches  200°  F.,  remove  the  mixture 
from  the  fire. 
To  this  add  the  mercurial  solution  (hot  or  cold  ?),  and,  with  a 
wooden  spatula,  stir  constantly  so  long  as  effervescence  continues, 
and  afterwards  occasionally  until  the  ointment  stiffens. 
The  mercurial  solution  was  added  all  at  once  to  the  melted  oil 
and  lard,  temp.  200°  F.  The  temperature  fell  to  160°,  then 
rapidly  rose  to  260°,  the  ointment  undergoing  a  violent  reaction, 
and  assuming  quite  a-  dark  brown  color.  The  temperature 
gradually  fell  to  220°,  at  which  temperature  the  reaction  gradu- 
ally ceased.    (Loss  of  weight  7  per  cent.) 
Experiment  §4. — This  was  one-eighth  part  of  a  formula  which 
has  been  used  by  the  writer  for  several  years, — in  fact  is  the  re- 
sult of  experiments  made  with  the  official  formula  during  the 
autumn  of  1863,  and  is  here  given  : 
Take  of  Mercury,  12  oz. 
Nitric  Acid,  sp.  gr.  1-42,  32  oz. 
Lard  (pressed),  36  oz. 
Neats-foot  Oil,  96  oz. 
All  by  weight. 
Put  the  mercury  into  a  three-pint  flask,  and  add  thereto  28 
oz.  of  the  nitric  acid;  -  let  it  remain  at  the  ordinary  temperature 
until  all  of  the  mercury  is  dissolved,  and  the  resulting  solution 
is  of  a  beautiful  green  color. 
Place  the  oil  and  lard  in  a  suitable  earthen  vessel,  of  at  least 
four  gallons  capacity,  and  gradually  heat  the  mixture  to  180°  F. 
Now  warm  the  mercurial  solution  to  160°  F.,  and  gradually 
add  it  to  the  oil  and  lard,  at  the  above  named  temperatures,  in 
portions  of  fl.5ii  at  a  time,  constantly  stirring  with  a  glass  or 
porcelain  stirrer ;  the  temperature  gradually  rises  to  190°,  200°, 
220°,  230°,  above  which  last  degree  it  must  not  be  allowed  to 
rise.  The  stirring  must  be  continued  so  long  as  effervescence 
continues ;  and  when  it  ceases,  and  the  ointment  has  cooled  to 
200°  F.,  add  the  remaining  4  oz.  of  nitric  acid,  and  stir  occa- 
sionally until  cool.    (Loss  10  per  cent.) 
The  result  of  the  above  formula  is  shown  by  sample  marked 
§4. 
Experiment  §5. — The  quantities  of  the  U.  S.  Pharm.  1860, 
