AmSSm'}  Method  for  Estimating  Morphia  in  Opium.  119 
pour  the  contents  of  the  tube  into  a  clean  one.  Take  next  100  grain 
measures  of  the  standard  solution  of  morphia,  and,  using  a  fresh  tube, 
repeat  the  operation  just  described.  Compare  now  the  two  rose- 
tinted  liquids  by  holding  the  tubes  side  by  side  between  the  eye  and 
a  white  cloud,  or  placing  them  against  thin  white  paper  attached  to  a 
window-pane.  If  the  colors  are  equal  in  intensity,  the  powdered 
sample  contains  10  per  cent,  of  morphia.  If  unequal,  add  to  the 
deeper  one  carbon  disulphide  in  small  successive  measured  quanti- 
ties— say  of  5  or  10  grain  measures  at  a  time,  as  may  seem  necessary 
— gently  mixing  it  in  with  a  glass  rod.  When  by  this  means  the  tints 
have  been  rendered  equal  in  depth,  the  calculation  is  simple. 
Let  v  =  volume  in  grain  measures  of  standard  color ; 
Let  v'  =  volume  in  grain  measures  of  sample  color  ; 
vf  X  10 
then   =  x  —  percentage  of  morphia  in  powdered  sample. 
*  j  •  p  *  i  <-  i  ,  •  j  •  100  —  w  x  x 
And  it  w  =  percentage  Joss  ot  weight  in  drying,   100" ~ 
=  percentage  of  morphia  in  moist  sample. 
Precaution. — The  carbon  disulphide  used  must  remain  colorless 
when  shaken  with  solution  of  iodic  acid. 
In  order  to  test  the  ability  of  the  eye  to  discern  slight  inequalities 
of  tint,  the  relative  quantities  of  iodine  in  the  standard  and  sample 
colors  were  sometimes  estimated  at  the  end  of  an  experiment  by  Du- 
pre's  method.  This  was  done  by  removing  the  supernatant  aqueous 
liquid  with  a  pipette,  washing  the  solution  of  iodine  with  distilled 
water,  transferring  it  to  a  stoppered  bottle,  and  adding,  with  vigorous 
shaking,  weak  chlorine  water  from  a  burette  until  the  color  just  dis- 
appeared. The  results  are  given  in  the  subjoined  table,  and  show,  I 
think,  that  the  eye  has  a  fair  claim  to  be  trusted.  When  a  number 
of  morphia  determinations  have  to  be  made,  the  use  of  this  iodi metric 
process  is  convenient,  as  only  a  single  daily  reference  to  the  standard 
is  then  needed. 
The  time  required  for  determining  the  morphia  value  of  opium  on 
the  above  plan  is  about  two  hours  and  a  half.  As  regards  accuracy 
and  reliability,  I  may  state,  that  so  far  as  my  experiments  have  gone 
— and  they  have  not  been  few — the  results  have  appeared,  after  care- 
ful  scrutiny,  to  be  nearer  approximations  to  the  truth  than  those  ob- 
tained by  the  ordinary  methods  by  precipitation.  I  have,  therefore, 
much  confidence  in  the  process.    Nevertheless,  I  am  ready  to  admit 
