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UNG.   HYDRARGYRX  NITR. 
slowly  during  the  night.  The  next  morning  I  melt  the  lard/ 
and  after  the  acid  solution  is  added  I  watch  the  chemical  action 
during  the  day.  The  following  morning  the  preparation  is 
finished  in  the  manner  hereafter  described. 
As  the  nitrous  acid  is  the  most  essential  agent  in  the  forma- 
tion of  the  ointment,  I  effect  the  solution  of  the  mercury  so  as 
to  lose  as  little  of  this  acid  as  possible.  I  therefore  allow  the 
solution  of  the  mercury  to  go  on  spontaneously  in  the  cold  and 
in  a  tall  covered  jar.  I  avoid  hereby  trouble  and  inconveni- 
ence ;  and  in  the  morning  I  find  a  complete  solution,  cold  and 
ready  for  use.  In  the  morning  I  melt  the  lard  on  a  water  bath, 
strain  it  into  an  open  glazed  pan,  and  add  the  oil  to  it  cold  to 
lower  the  temperature.  I  stir  the  two  well  together,  and  wait 
until  the  mixture  is  about  130°  Fahr.,  when  I  pour  the  mercurial 
solution  gently  into  it,  and  allow  the  whole  to  stand  undisturbed 
for  some  time.  When  the  ointment  begins  to  set  at  the  sides 
of  the  vessel,  and  on  the  surface,  I  move  these  solid  portions 
gently,  and  guide  them  into  the  warmer  part,  and  wait  again 
until  it  is  necessary  to  repeat  this  operation,  now  and  then  draw- 
ing the  spatula  backwards  and  forwards  through  the  entire  mass. 
As  the  whole  becomes  firmer  and  firmer,  I  increase  the  stirring, 
and  continue  it  at  intervals  through  the  whole  day.  The  next 
morning  I  find  a  spongy  mass  with  a  high  raised  crust,  rather 
harder  than  the  interior  portion,  and  generally  a  small  quantity 
of  acid  liquid  at  the  bottom  of  the  pan.  I  now  stir  and  beat  the 
mass  vigorously  for  some  time  until  the  spongy  ointment  softens 
under  the  spatula,  and  the  liquid  becomes  thoroughly  mixed, 
when  the  color  becomes  of  a  beautiful  canary  yellow,  and  my 
care  and  trouble  are  rewarded  with  an  ointment  everything 
that  can  be  desired  in  appearance  and  consistence.  I  have 
still  to  add  a  few  words  on  the  ingredients  and  materials  which 
concern  this  ointment.  First  of  all  I  select  the  finest  and  best 
lard,  as  the  goodness  of  the  ointment,  its  color  and  keeping 
properties,  depend  a  good  deal  on  the  quality  of  this  article. 
Next,  I  avoid  the  use  of  all  materials  which  are  likely  to  be 
acted  on  by  the  acid  solution.  Even  the  wooden  spatula  of  the 
laboratory  I  suspiciously  discard  for  one  of  stone  ware ;  and 
when  I  have  my  lard  and  oil,  mercury  and  nitric  acid  in  proper 
condition,  my  last  look  is  to  see  that  my  vessels  are  really  per- 
fectly clean.— Chem.  Neivs,  Feb.  11,  I860. 
