ON  THE  REVISION  OF  THE  U.  S.  PHARMACOPOEIA. 
5T 
cumstances,  gives  an  odor  of  chlorine  and  muriatic  acid,  and 
produces  a  yellow,  oily  liquid,  which  collects  around  the  edges 
of  the  surface  in  contact  with  the  bottle.  Spirit  of  nitre  be- 
comes colorless-'and  acid  in  a  few  hours.  Hoffmann's  anodyne  be- 
comes quite  acid,  and  many  tinctures  and  powders  change  their 
sensible  properties  materially. 
Hydrargyri  lodidum. 
In  a  chemical  point  of  view,  this  preparation  may  be  regarded 
as  one  of  the  most  indefinite  and  uncertain  of  the  Materia  Me- 
dica ;  whilst  therapeutically  it  is  certainly  very  far  from  being 
what  is  desired.  From  being  mild  and  manageable  at  times,  it 
varies  so  that  harsh  and  even  violent  effects  are  not  unfrequently 
encountered  from  its  use.  As  prepared  strictly  in  accordance 
with  the  Pharmacopoeia,  it  always  contains  the  red  iodide,  and 
this  in  various  proportions,  according  to  slight  variations  in  the 
management.  So  that  it  must  have  been  an  oversight  in  those 
who  constructed  the  present  formula,  that  a  careful  washing 
with  str5ng  alcohol  was  omitted.  When  made  by  the  officinal 
formula,  in  the  dark,  or  by  artificial  light,  carefully  and  tho- 
roughly washed  by  digestion  and  decantation  with  strong  alco- 
hol, dried  in  the  dark,  and  then  carefully  preserved  from  the 
light,  it  is  probably  in  its  best  condition  for  therapeutic  appli- 
cation. But  even  then,  though  free  from  red  iodide  it  contains  a 
large  preportion  of  the  yellow  or  subiodide,  and  of  metallic  mer- 
cury. And  these  proportions  vary,  probably,  every  time  it  is 
made,  even  though  made  by  the  same  person  from  the  same 
materials.  The  writer  has  occasionally  seen  it  so  free  from  me- 
tallic mercury  that  it  would  but  slightly  amalgamate  a  surface 
of  gold  foil  when  rubbed  upon  it,  but  has  never  seen  a  specimen, 
however  carefully  made,  or  by  whatever  process,  that  would  not 
very  sensibly  affect  the  gold  when  rubbed  upon  it ;  whilst  two 
specimens  made  as  far  as  practicable  in  the  same  manner,  would 
affect  the  gold  differently.  The  proportion  of  yellow  iodide 
must  of  course  vary  with  the  proportion  of  metallic  mercury, 
and  thus  the  color  of  the  preparation,  as  commonly  met  with,  is 
almost  always  different.  It  is  generally  described  as  being 
green  or  yellowish  green,  but  when  well  washed  it  is,  though 
of  varying  tint,  always  of  a  greenish  yellow  color ;  the  brighter 
