2  Mayer's  Reagent  for  Estimating  Alkaloids.  { Am  jinU,riS?arm* 
The  mode  of  conducting  a  titration  must  have  an  important  influ- 
ence on  the  result.  Some  direct  to  allow  the  precipitate  to  subside 
after  each  addition  of  reagent,  and  test  a  drop  of  the  clear  supernatant 
fluid  with  a  drop  of  the  reagent.  A  more  common  practice,  and  that 
which  I  have  adopted  in  most  of  my  experiments,  is  to  filter  the  fluid 
after  each  successive  addition  of  reagent,  using  the  same  filter,  which 
must  be  only  large  enough  conveniently  to  hold  the  whole  of  the 
fluid.  The  titration  is  concluded  when  the  addition  to  the  filtered 
fluid — having  a  volume  of  10  cc. — of  two  drops  of  reagent  fails  to  pro- 
duce a  permanent  turbidity.  In  some  cases  the  reagent  as  it  drops 
into  the  fluid  produces  a  transient  turbidity,  clearing  up  at  once, 
while  addition  of  a  larger  quantity  of  the  reagent  produces  a  perma- 
nent precipitate.  The  formation  of  this  precipitate  being  obviously 
conditioned  by  the  presence  of  a  large  excess  of  reagent,  it  is  proper 
to  ignore  it. 
No  doubt  the  results  of  a  titration  will  coincide  more  nearly  with 
what  theory  requires  if  a  considerable  length  of  time  is  allowed  to 
elapse  after  each  addition  of  reagent,  but  this  manner  of  conducting 
the  operation  robs  it  of  its  single  advantage — rapidity  of  execution — 
and  is  not  to  be  recommended,  since,  after  all,  there  will  be  consider- 
able and  often  quite  capricious  departures  from  theoretical  figures. 
The  method,  however,  of  carrying  out  titrations  with  Mayer's 
reagent  that  has  been  recently  recommended  by  Frank  S.  Hereth1 
secures  the  advantages  of  the  plan  just  mentioned  without  extending 
the  time  actually  consumed  in  the  operation.  The  method  is  as  fol- 
lows: Knowing  approximately  the  alkaloidal  strength  of  the  solution 
to  be  examined,  provide  half  a  dozen  or  more  test  tubes  or  vials,  and 
into  each  measure  10  cc.  of  the  solution.  To  the  first  add  a  quantity 
of  reagent  a  little  less  than  that  likely  to  be  required ;  to  the  second  a 
somewhat  larger  quantity,  and  so  on.  Let  the  test  tubes  stand  at 
least  eight  hours,  then  test  a  portion  of  the  clear  fluid  from  each  with 
a  drop  of  Mayer's  reagent.  The  first  one  which  fails  to  react  ob- 
viously has  received  a  quantity  of  reagent  a  little  more  than  sufficient 
for  the  precipitation,  and  it  will  not  be  difficult  to  judge  by  the 
amount  of  cloudiness  produced  in  it  just  what  excess  of  reagent  is 
present.  Of  course  the  value  of  the  titration  equivalent  will  have  to 
be  determined  anew  experimentally,  if  this  method  is  to  be  adopted. 
i  Pharmaceutical  Record,  July  1, 1886. 
