UNGUENTUM  HYDRARGYRI  NITRATIS. 
213 
?15. — Pharmacopoeia  U.  S.  America,  1840.  Pharmacopoeia  U.S.America, 
1850. 
^16. — Pharmacopoeia  London,  1851. 
^17. — Pharmacopoeia  U.  S.  America,  1860. 
^18. — Pharmacopoeia  British,  London,  1864. 
|19, — Pharmacopoeia  British,  London,  1867. 
^20. — Process  in  use  by  the  writer,  Thos.  J.  Covell,  since  1863,  and  detailed 
in  experiment  ^4. 
Only  two  of  the  nineteen  formulas  were  selected  for  experi- 
ment, the  first  being  that  of  the  British  Pharmacopoeia,  1867, 
and  the  second  that  of  the  United  States  Pharmacopoeia,  1860. 
The  formula  of  the  British  Pharmacopoeia  is  §19  of  the  table, 
and  the  directions  are  thus  given : 
Dissolve  the  mercury  in  the  nitric  acid  with  the  aid  of  a  gen- 
tle heat  (query,  what  temperature  ?) ;  melt  the  lard  in  the  oil  by 
a  steam  or  water  bath,  in  a  porcelain  vessel  capable  of  holding 
six  times  the  quantity ;  and  while  the  mixture  is  hot  (what 
temp.  ?)  add  the  solution  of  mercury  (query,  all  at  once,  or 
gradually  ?),  also  hot  (what  temp.  ?),  mixing  them  thoroughly. 
If  the  mixture  does  not  froth  up,  increase  the  heat  till  this 
occurs.    Keep  it  stirred  until  cold. 
Experiment  §1. — The  quantities  of  Br.  Ph.,  §19,  were  taken. 
The  mercury  was  allowed  to  dissolve  by  the  aid  of  the  heat, 
generated  by  the  reaction,  about  125°  F. 
The  lard  and  oil  were  heated  to  200°  F.,  when  the  solution  of 
mercury,  125°  F.,  was  gradually  added,  in  portions  of  fl.^ii,  at 
intervals  of  two  to  five  minutes,  that  the  reaction  might  not  be 
too  violent,  and  easily  controlled.  The  temperature,  after  the 
first  addition,  rose  rapidly  to  230°  F.  ;  after  the  second  it  fell 
to  226°  ;  and  after  each  succeeding  addition  of  the  mercurial  so- 
lution fell  to  219°,  216°,  214°,  then  rose  to  220°,  then  fell  to 
218°,  200°,  190°,  at  which  it  remained  until  the  reaction  had 
apparently  ceased.  It  was  constantly  stirred  throughout  the 
entire  process.    (Loss  in  weight  13*63  per  cent.) 
Experiynent  §3. — The  quantities  of  the  U.  S.  Pharm.,  §17, 
were  taken,  the  directions  of  which  are  as  follows  : 
Dissolve  the  mercury  in  the  acid  (hot  or  cold  ?) ;  then  heat  to- 
gether the  oil  and  lard  in  an  earthen  vessel  (how  long  ?)  and, 
