6  Mayer's  Reagent  for  Estimating  Alkaloids.  {Am  ja0™^.™' 
of  reagent.  The  quantity  of  mercury  which  combines  with  the  alka- 
loid, although  not  perhaps  absolutely  constant,  does  not  show  any 
wide  range  of  variation,  particularly  when  the  conditions  of  the  pre- 
cipitation are  similar.  Some  simple  mode  of  estimating  the  excess  of 
reagent  present  at  the  end  of  the  titration— or,  better,  after  several 
hours  have  elapsed — is  therefore  obviously  a  desideratum.  Prof. 
Mayer's  plan  of  titrating  the  excess  with  decinormal  silver  nitrate — 
apart  from  other  considerations— ignored  the  circumstance  that  the 
reagent  contains  an  excess  of  iodine  over  and  above  what  takes  part 
in  the  reaction  and  that  it  also  contains  chlorine.  Besides,  the  alka- 
loids requiring  titration  are  not  unfrequently  in  the  form  of  chlorides. 
In  order  to  obtain  any  useful  results  by  Prof.  Mayer's  method,  a 
complicated  mathematical  calculation  is  required,  of  which  the  data 
themselves  cannot  be  assumed  a  priori  to  be  known.  , 
Observing  that  the  precipitate  produced  by  silver  nitrate  in  a  fluid 
containing  Mayer's  reagent  was  at  first  bright  chrome  yellow,  while, 
on  continued  addition  of  the  silver  solution,  the  successive  portions  of 
precipitate  passed  from  a  bright  to  a  pale  yellow  color,  it  occurred  to 
me  that  it  might  be,  after  all,  possible  to  estimate  the  excess  of  mer- 
cury by  this  means,  assuming  that  the  bright  yellow  compound  is  a 
double  iodide  containing  mercury.  It  appears,  however,  that  this 
compound  is  not  formed  exclusively  at  the  beginning  of  the  reaction, 
and  the  color  fades  so  gradually  that  no  exact  conclusions  could  be 
drawn  from  the  indications  presented,  although  they  serve  as  a  rough 
measure  of  the  amount  of  the  excess. 
Incidentally,  I  desire  to  call  attention  to  the  existence  of  the  bright 
yellow  compound  in  question  which  I  regret  that  I  have  not  had  time 
to  study.  It  is  remarkable  that  it  is  not  at  all  sensitive  to  light.  Its 
composition  and  properties  are  worthy  of  investigation. 
Finding  that  strychnine  was  precipitated  more  perfectly  than  almost 
any  other  alkaloid,  and  with  less  variation  under  different  conditions, 
I  thought  it  might  be  practicable  to  estimate  the  excess  of  reagent  in 
a  solution  by  the  use  of  this  alkaloid,  and  the  plan  is  one  that  proves 
measurably  successful.  After  finishing  the  titration  in  the  ordinary 
way,  add  to  the  filtered  fluid  one,  two  or  three  cc.  of  a  solution  of 
strychnine  of  a  strength  corresponding  exactly  with  that  of  the  Mayer's 
reagent  used.  Filter  and  titrate  the  excess  of  strychnine  with  Mayer's 
reagent,  and  by  deducting  the  quantity  used  of  the  latter  from  the 
amount  of  strychnine  solution  added,  the  required  excess  is  obtained. 
