ASSAY  OF  ALKALOIDS. 
9 
Mr.  Groves'  alkaloids  vary  with  the  equivalent  between  one, 
and  four-tenths  of  one  per  cent.,  and  the  quantities  with  which 
he  has  compared  and  by  which  he  would  subvert  my  numbers  are 
one  hundred  grains  of  these  liquids,  a  large  sized  teaspoonful. 
These,  morphia  and  all  others,  he  compares  with  a  test  liquor  of 
exactly  the  strength  of  my  original  (l-5th)  troy  solution. 
As  a  consequence,  wherever  I  have  prescribed  dilute  solutions 
in  both  cases,  as  less  than  one-half  per  centum  of  strychnia, 
and  allow,  as  in  this  instance,  the  weak  mercuric  solution,  the 
numbers  agree  well  enough  to  receive  Mr.  Groves'  approbation. 
But  mark  the  difference  in  the  case  of  morphia : 
Of  his  test  liquor. 
Mr.  Groves  supposes,  according  to  his  theory,  that 
he  requires  100  grains. 
He  actually  requires  70  " 
Reduced  to  his  numbers,  my  metrical  solution  is 
consumed  to  the  extent  of  75§  « 
Reduced  to  his  numbers,  my  strong  troy  solution 
with  Groves'  solution  of  morphia  is  consumed  to 
the  extent  of  78  « 
My  theory  requires  75  " 
The  strength  of  the  solution  of  morphia,  I  have  stated  in  my 
assay  of  opium,  should  be  such  that  after  precipitation  with  the 
reagent  the  whole  bulk  of  precipitate  and  liquid  when  diluted 
for  filtering  and  testing  with  silver  may  represent  not  less  than 
0*3  gramme  of  morphia  in  100  c.  c. ;  that  is,  1  c.c.  is  equal  to 
the  filtrate  from  0-003  gramme  of  morphia  after  precipitation ; 
the  space  of  0-3  c.  c,  supposed  to  be  occupied  in  the  100  c.c. 
by  the  dry  precipitate,  is  not  counted.  This  is  almost  precisely 
the  dilution  of  Mr.  Groves'  original  solution  (=0-303  grain  in 
100).  The  difference  between  the  two  modes  of  assaying  then 
is,  that  he  measures  a  dilute  solution  with  a  test  liquor  of  one- 
fifth  the  strength  of  mine,  while  I  have  assayed  with  mercury 
a  more  concentrated  solution  (1  p.  c),  and  after  reducing  the 
liquid  to  the  strength  of  the  original  one  of  Mr.  Groves,  measure 
it  again  with  silver.  If  any  cause  for  error  may  arise,  dilution 
for  instance,  it  is  existing  in  his  solution  from  the  beginning,  in 
mine  only  after  removal  of  the  precipitate ;  and  while  the 
former  is  constantly  growing  weaker  by  the  addition  of  test- 
