8 
ASSAY  OF  ALKALOIDS. 
the  laughable  side  of  this  incident,— -in  attempting  to  bring 
into  discredit  my  assay  of  atropia  by  controverting  its  results, 
he  entirely  overlooks  the  fact  that  in  so  doing  he  also  upsets 
one  of  his  own  formulae,  that  of  atropia  +  HI  +  2HgI.  I  have 
never  used  any  other  for  it. 
In  my  original  paper  I  recommended  measuring  in  the  liquid 
portion  of  the  mixture  holding  the  precipitate,  the  excess  of 
iodine  and  chlorine  by  a  solution  of  silver,  and  without  filtering. 
The  latter  is  quite  practicable  in  the  case  of  atropia  and  some 
bases  where  the  precipitates  form  a  resinous  mass,  but  is  not 
generally  applicable,  and  was  withdrawn  by  me  in  my  paper  on 
opium.  Mr.  Groves  falls  foul  of  this  non-filtration,  but  admits 
that  there  are  a  few  exceptions  in  which  it  may  be  done,  and 
that  I  had  myself  directed  filtration  ;  yet  he  omits  to  state  that 
atropia  is  one  of  his  eases  of  exception. 
Something,  I  am  sure,  altogether  unheard  of  in  reviewing  a 
method  in  chemistry,  and  especially  a  volumetric  process,  is  that 
the  critic  does  not  in  the  least  pretend  to  work  with  the  same 
solutions  as  the  original  author,  but  uses  liquids  of  a  degree  of 
dilution  which  he  imagines  better  adapted  for  the  purpose. 
Now,  whether  this  be  so  or  not,  there  are  certain  alkaloids 
which  show  variations  according  to  dilution  similar  to  those  pro- 
duced in  Bunsen's  iodine-assay,  according  to  whether  differ- 
ent solutions  of  sulphurous  acid  are  employed.  My  equiva- 
lents of  iodohydrargyrate  are  all  taken  with  a  tenth  normal 
liquid  against  one  percentum  of  alkaloid  in  solution.  I  also 
gave  a  grain  or  troy-test  liquid  of  one-fifth  the  strength  of  my 
metrical  solution.  But  in  the  paper  on  opium  I  stated  that 
owing  to  the  solubility  of  the  precipitate  with  morphia,  the 
former  troy-liquid  was  too  weak  to  give  accurate  results,  and 
that  one  of  five  times  the  strength  was  to  be  used,  that  is,  of 
the  same  strength  as  the  metrical  solution.  For  the  assay  of 
strychnia  and  brucia,  however,  I  retained  the  original  weak  so- 
lution as  sufficiently  accurate  for  pharmaceutical  purposes. 
My  solutions  of  alkaloid  contain  either  one-half  or  one  per 
cent.,  at  least,  in  those  cases  where  I  have  published  detailed 
researches.  In  these  I  never  use  less  than  10  cubic  centimeters, 
about  225  drops,  but  in  most  cases  20,  30,  or  40  c.  c,  repeat- 
edly and  in  succession. 
