^°i-go^y-ig|_^^"°-}       Mayer's  Reagent  for  Alkaloids. 
489 
average  between  '0142  and  '0141,  this  would  give  us  a  percentage 
of  ( 01415  X  6-3)  X  10==0-89  per  cent,  alkaloid. 
THE  REAGENT. 
All  titrations  and  tables  in  this  paper  refer  to  a  solution  containing 
6*775  grammes  of  mercuric  chloride  and  25  grammes  of  potassium 
iodide  to  the  litre  ( n ),  and  is  consequently  a  solution  of  half  the 
strength  of  that  originally  recommended  by  Mayer. 
METHOD  OF  TITRATION. 
As  the  method  of  titration  in  some  instances  at  least  influences  the 
results,  it  is  recommended  that  all  who  may  use  these  tables  should 
pursue  the  following  convenient  course.^  Run  in  from  J  to  1  cc.  of 
reagent,  after  stirring  allow  to  stand  one  or  two  minutes  before  again 
running  in  a  like  quantity,  and  as  before,  after  stirring,  allow  to  stand 
a  minute  or  two,  finally  as  it  becomes  apparent  that  the  end  of  the 
reaction  is  nearly  reached  the  fluid  is  to  be  passed  through  a  small  dry 
filter  paper,  best  of  a  size  to  just  conveniently  hold  all  of  the  liquid, 
allowing  most  of  the  fluid  to  pass  through  before  again  testing  with  a 
drop  of  the  reagent.  The  final  end  is  best  determined  by  taking  out 
four  or  five  drops  of  the  filtrate  in  a  watch  glass  placed  on  a  dark 
surface  and  adding  one  drop  of  the  reagent.  If  a  precipitate  does  not 
appear  on  standing  half  a  minute  or  so  the  end  may  be  considered  as 
reached.  If  a  precipitate  does  appear  the  fluid  is  to  be  returned  to 
the  main  portion  and  the  operation  continued. 
ACONITINE. 
The  writer  reported  a  number  of  experiments  some  time  ago  on  this 
alkaloid.^  Results  of  titrations  are  on  the  whole  very  satisfactory,  and 
the  end  reaction  is  quite  distinct  and  well  marked.  The  alkaloid  may 
be  regarded  as  belonging  on  the  list  of  those  for  which  Mayer's  reagent 
may  be  used  advantageously  as  a  means  of  estimation.  Experiment 
shows  each  cc.  of  the  reagent  precipitates  in  faintly  acid  solutions 
amounts  as  follows  for  different  degrees  of  dilution : 
1  The  method  of  A.  B.  Lyons  slightly  modified  for  the  determination  of  the 
final  end. 
2Pharm.  Era,  ii-20  from  New  Idea,  Oct.  1887-616. 
