128 
LIQUOR  OPII  COMPOSITUS. 
it  will  generally  be  safest  to  perform  two  assays,  because  from 
the  heterogeneous  and  varying  character  of  opium,  the  process 
of  morphiornetry  is  rather  unusually  difficult.  The  method  of 
assay  adopted  is  not  the  most  accurate  one,  and  always  gives 
results  a  little  too  high,  though  the  amount  of  narcotine  color- 
ing matter,  &c,  weighed  as  morphia,  is  nearly  counterbalanced 
by  the  portion  of  morphia  held  by  the  mother  liquor.  It  is, 
however,  beyond  all  measure  the  most  simple  and  the  most 
easy,  and  most  susceptible  of  a  definite  practical  description, 
while  it  is  sufficiontly  accurate  to  accomplish  in  great  measure 
the  object  of  uniformity.  Through  some  disturbing  influence 
of  the  ether  and  oil  of  wine  the  finished  solution  is  much  more 
difficult  to  assay  by  the  same  process.  The  solution  requires  to 
be  evaporated  at  a  low  temperature  for  twenty-four  hours  before 
the  attempt  to  precipitate  it. 
The  management  directed  in  the  assay,  by  which  the  alcohol 
added  is  divided,  and  one-half  mixed  with  the  ammonia,  is  neces- 
sary in  order  that  the  morphia  shall  be  slowly  precipitated  in 
the  form  of  dense  crystals,  and  these  be  tolerably  free  from 
coloring  matter;  and  the  slowness  with  which  it  is  deposited 
makes  it  necessary  that  the  full  time  directed  be  given  to  this 
step.  Then  the  morphia  is  almost  all  crystallized  out,  and  is  in 
such  a  form  that  the  mother  liquor  may  be  poured  off  from  it 
generally  to  the  last  drop  without  disturbing  the  crystals,  and 
thus  the  complication  of  a  filter  is  avoided.  The  capsule  used 
should  be  shallow,  and  should  not  be  covered  during  the  time  of 
depositing  the  morphia,  because  solutions  of  ammonia  are  very 
variable  in  strength  ;  and  if  an  excess  of  ammonia  be  used  within 
certain  limits,  it  will  pass  off  during  twenty-four  hours'  expo- 
sure, and  allow  the  morphia  to  be  deposited  more  perfectly. 
The  drying  and  weighing  of  the  contents  of  the  capsule,  while 
still  undisturbed  within  it,  is  easily  performed,  and  avoids  sources 
of  loss  and  error.  The  four  hundred  and  sixty-four  grains  of 
the  solution  directed  for  the  assay  is  exactly  one  fluid  ounce, 
and  the  eighty-five  parts  directed  as  the  standard  of  dilution  for 
the  solution  before  assaying  is  exactly  equal  to  eighty  parts  by 
measure ;  that  is,  eighty-five  avoirdupois  ounces  of  the  solution 
measures  exactly  eighty  fluid  ounces.  One  fluid  ounce,  then, 
having  been  taken  for  assay,  leaves  seventy-nine  fluid  ounces  or 
