364     ON  PREPARING  RED  OXIDE  OF  MERCURY  OINTMENT. 
the  binoxide  has  been  directed  to  be  prepared  in  the  British  and 
in  the  preceding  London  Pharmacopoeias. 
In  the  British  Pharmacopoeia,  under  the  name  of  red  oxide 
of  mercury,  it  is  directed  to  be  prepared  by  the  action  of  nitric 
acid  on  metallic  mercury,  and  the  subsequent  application  of  heat 
to  a  mixture  of  the  resulting  nitrate  with  metallic  mercury. 
In  the  last  London  Pharmacopoeia,  under  the  name  of  nitric 
oxide  of  mercury,  it  is  prepared  by  the  application  of  heat  to  the 
nitrate. 
In  the  last  London  Pharmacopoeia  but  one,  two  different  pro- 
cesses are  given :  the  one  is  almost  identical  with  the  process 
last  mentioned,  and  its  product  is  called  the  nitric  oxide ;  the 
other  is  the  decomposition  of  a  solution  of  corrosive  sublimate 
by  a  solution  of  potash,  and  its  product  is  termed  the  binoxide. 
The  ointment  in  this  last-mentioned  Pharmacopoeia  is  prepared 
from  the  nitric  oxide,  the  binoxide  being  used  only  in  the  prepa- 
ration of  the  bicyanide  of  mercury.  It  is  my  object  this  evening 
to  show  that  the  binoxide  should  have  been  chosen  for  the  oint- 
8  ment  rather  than  the  nitric  oxide,  and  to  give  what  I  trust  may 
be  thought  sufficient  reasons  for  advocating  the  revival  of  the 
former  in  the  British  Pharmacopoeia,  not  indeed  for  the  purpose 
for  which  it  was  formerly  introduced,  but  as  an  infinitely  better 
substance  than  that  now  used  for  the  preparation  of  the  red 
oxide  of  mercury  ointment. 
Oxide  of  mercury  ointment  appears  always  to  have  been  pre- 
pared with  the  nitric  oxide ;  it  is  so  directed  not  only  in  the 
British  Pharmacopoeia,  but  in  the  London  Pharmacopoeias  of 
1851,  1836,  1824  and  1809. 
One  possible  reason  for  this  preference  for  the  nitric  oxide  is, 
that  in  the  condition  of  scales,  the  oxide  of  mercury  is  less 
capable  of  adulteration,  since  its  physical  properties,  e.  g.  the 
reflection  of  light  from  the  glittering  scales,  enable  it  to  be  more 
readily  recognized. 
But  one  can  readily  understand  how  the  so-called  binoxide 
should  be  a  more  active  remedy. 
A  mere  comparison  of  the  naked-eye  appearance  of  the  one 
with  that  of  the  other  will  suffice  to  show  how  much  smaller  the 
particles  of  the  binoxide  are :  theirs  is  a  paler  and  a  duller  color. 
