LIQUOR  OPII  COMPOSITUS. 
53 
The  process  of  assay  consists  simply  in  precipitating  the  mor- 
phia from  an  aliquot  part  of  this  solution  by  means  of  ammonia, 
— drying  and  weighing  the  morphia,  and  applying  the  result,  by 
multiplication,  to  the  remainder  of  the  solution,  so  as  to  ascer- 
tain the  quantity  of  morphia  which  this  contains.  By  this,  of 
course,  the  farther  dilution  and  adjustment  are  made.  Although 
this  process  of  assay  does  not  pretend  to  be  critically  accurate, 
yet  it  will  be  so  in  proportion  to  the  care  and  nicety  with  which 
the  different  steps  are  followed  as  now  to  be  described  ;  and 
whilst  without  any  extraordinary  degree  of  skill  it  may  be  so 
conducted  as  to  indicate  within  three  or  four  tenths  of  a  per 
cent,  of  the  morphia  value  of  the  opium  used,  it  can  hardly  be 
so  mismanaged  as  not  to  come  within  one  per  cent,  of  the  true 
value. 
Take  one-seventeenth  part,  or  463  grains  =  30  grammes,  or 
about  1  f§,  =30  cc.  of  the  solution,  and  put  it  into  a  small  tared 
capsule,  and  set  the  capsule  in  a  saucer  or  plate  which  contains 
a  shallow  stratum  of,  or  is  about  half  filled  with,  water.  Then 
make  a  mixture  of  equal  parts  of  officinal  water  of  ammonia 
and  stronger  alcohol,  and  take  of  this  mixture  about  77  grains  or 
5  grammes,  or  5  cc,  rather  more  than  less, — and  add  it  to  the 
contents  of  the  capsule.  Stir  the  mixture  and  then  cover  the 
capsule  with  a  large  beaker  or  other  glass  vessel,  inverted  so 
that  the  edge  of  the  beaker  or  vessel  rests  on  the  saucer  or  plate 
in  the  water,  and  allow  the  whole  to  stand  at  rest  during  two 
days  or  thereabouts.  If  there  be  no  alcohol  added  to  the  water 
of  ammonia,  it  will  sometimes  precipitate  a  portion  of  the  mor- 
phia at  once,  and  with  it  an  undue  proportion  of  coloring  matter. 
When  diluted  with  alcohol  and  in  a  somewhat  alcoholic  solution 
the  morphia  goes  down  gradually  and  slowly  in  the  form  of  a 
crystalline  crust  of  a  chestnut-brown  color,  which  adheres  to 
the  bottom  and  sides  of  the  capsule.  The  precipitation  is  gen- 
erally complete  in  24  hours,  often  in  12  hours,  but  is  occasion- 
ally retarded  by  unknown  causes.  It  rarely  increases  after  48 
hours,  however,  and  this  period  is  fixed  in  order  to  render  the 
result  pretty  secure.  The  quantity  of  ammonia  used  may  vary 
considerably  without  materially  affecting  the  result.  The  quan- 
tity indicated  is  quite  enough  for  opium  of  the  best  quality,  but 
