54 
LIQUOR  OPII  COMPOSITUS. 
it  may  be  increased  one-fourth,  or  even  one-half  without  much 
disadvantage.  The  morphia  thus  precipitated  is  not  pure,  but 
contains  coloring  matter  enough  to  give  it  a  light  brown,  or  a 
chestnut-brown  color.  The  quantity  of  coloring  matter  present 
is,  in  weight,  surprisingly  small,  and  is  fully  counterbalanced 
by  the  small  proportion  of  morphia  which  refuses  to  crystallize 
out.  The  results  are  therefore  pretty  accurate,  or  at  least  prac- 
tically accurate.  If  the  little  capsule  with  the  assay  be  allowed 
to  stand  merely  covered  with  paper  or  a  watch-glass  for  the  48 
hours,  some  of  the  solution  will  evaporate  away,  and  form  a 
hard  ring  of  dried  extractive  matter  upon  the  capsule  all  round 
the  edge  of  the  liquid,  and  this  would  be  subsequently  weighed 
as  morphia.  A  pellicle  forms  on  the  surface  too,  and  in  whole 
or  in  part  remains  in  the  capsule  when  the  mother  liquor  is 
poured  off.  By  the  simple  device  of  covering  the  capsule,  and 
preventing  all  change  of  air  by  a  water  joint,  as  described,  all 
this  inconvenience  is  avoided.  And  beside,  the  water  absorbs 
the  vapor  of  ammonia  as  the  excess  of  this  precipitant  is  given 
off"  from  the  solution,  and  diminishes  this  excess  about  as  well 
as  if  the  capsule  was  left  exposed  for  it  to  fly  off".  At  the  end 
of  the  48  hours  the  mother-liquor  is  poured  olf  clean  from  the 
adherent  crust  of  morphia  which  lines  the  capsule,  and  the  cap- 
sule is  supported  on  edge  upon  some  folds  of  bibulous  paper  for 
half  an  hour  to  drain.  It  is  then  put  in  a  larger  capsule  on  the 
water  bath  for  an  hour  to  dry,  when  it  is  ready  for  weighing. 
This  weighing  should  be  done  on  a  scale  sensitive  to  about  the 
eighth  or  the  fourth  of  a  grain,  and  with  good  weights  of  course. 
The  capsule  and  contents  are  weighed,  and  the  tare  or  weight  of 
the  capsule  is  subtracted  ;  and  the  weight  of  morphia  thus  as- 
certained will  be  in  proportion  to  the  quality  of  the  opium.  If 
the  powdered  opium  be  within  the  officinal  limit  the  morphia 
will  weigh  not  less  than  7*72  grains  or  0-5  gramme,  but  it  may 
weigh  anywhere  between  this  and  say  15*4  grains  or  1  gramme. 
Now  as  the  whole  of  the  solution  represented  the  whole  of  the 
opium,  and  as  one-seventeenth  of  the  solution  has  yielded  a 
quantity  of  morphia  which  is  now  known,  it  is  only  necessary 
to  multiply  this  quantity  by  17  in  order  to  know  what  the  whole 
solution  would  have  yielded  if  precipitated  in  this  way  ;  or  to 
