AmNovUr'i9i8arm '}       Determination  of  Morphine.  791 
Remarks  on  the  Foregoing  Method. 
Calculation  of  Results. — The  calculation  of  results  is  made 
strictly  according  to  the  stoichiometrical  relations  involved.  It  is 
not  necessary  to  adhere  strictly  to  the  quantities  and  aliquot  parts 
laid  down  above,  but  they  are  those  which  experience  has  shown  to 
be  most  often  convenient.  There  are  no  conventional  "  correc- 
tions "  to  be  applied,  as  in  most  standard  methods  for  the  assay  of 
opium,  so  that  much  greater  flexibility  of  detail  is  possible. 
Possible  Objections  to  the  Method. — The  most  obvious  objection 
that  can  be  raised  is  to  the  repeated  taking  of  aliquot  parts  as 
involving  an  increasing  possible  error.  Of  course,  the  'measure- 
ments thus  involved  must  be  made  with  due  care,  and  properly 
graduated  vessels  must  be  used.  Under  such  conditions  even  the 
theoretical  errors  involved  become  insignificant.  In  practice,  the 
results  obtained  are  excellent,  as  shown  under  the  heading  "  Experi- 
mental Data." 
The  chemical  accuracy  of  every  step  has  been  shown  in  Part  I, 
so  that  these  favorable  results  cannot  be  wholly  attributed  to  a 
"  balancing  of  errors." 
Special  Precautions. — Experience  has  shown  that  certain  pre- 
cautions are  necessary  to  ensure  complete  extraction  of  morphine 
and  to  avoid. the  formation  of  emulsions  during  the  process. 
1.  The  volume  of  the  aqueous  solution  to  be  extracted  should  be 
somewhat  less  than  that  of  the  chloroform-alcohol  mixture  with 
which  it  is  to  be  shaken. 
2.  The  amount  of  inorganic  salts  in  this  solution  should  be  as 
small  as  possible.  For  this  reason  the  addition  of  acids  and  alkalis 
following  the  precipitation  of  the  barium  sulphate  should  be  made 
as  sparingly  as  possible. 
3.  The  evaporation  should  be  conducted  as  rapidly  as  possible. 
Some  Chinese  pills  appear  to  yield  a  soluble  substance  which,  on 
oxidation,  encourages  the  formation  of  emulsions.  No  serious 
amount  of  this  is  formed  if  the  evaporation  is  conducted  quickly, 
but  exposure  of  a  large  surface  of  liquid  during  slow  evaporation 
is  very  prejudicial.  The  use  of  a  platinum  evaporating  dish  is, 
therefore,  very  advantageous. 
4.  Should  the  pills  to  be  examined  contain  soap,  sulphates,  or 
other  substances  that  react  with  barium  hydroxide,  special  measures 
must  be  taken.  The  lines  on  which  such  pills  may  be  treated  are 
indicated  in  Experiment  30. 
