Am'ja0nuyif87.arm"}  Mayer's  Reagent  for  Estimating  Alkaloids. 
3 
Hitherto  Mayer's  reagent  has  been  employed  almost  exclusively 
in  the  volumetric  method.  May  we  not  hope  to  find  it  more 
satisfactory  to  weigh  the  precipitates  produced,  and  so  ascertain  the 
quantity  of  alkaloid  present  ?  That  depends  of  course  on  the  con- 
stancy of  composition  of  the  precipitates  produced.  In  my  experi- 
ments I  have  given  attention  to  this  point  also.  I  find  that  most  of 
the  precipitates  vary  considerably  in  weight  under  varying  conditions. 
The  weight  of  the  precipitate  often  increases  materially  if  it  is  allowed 
to  stand  some  hours  before  collecting. 
I  have  tabulated  below  some  of  the  results  of  these  experiments.  In 
most  cases  the  precipitates  were  collected  shortly  after  they  were 
formed,  on  a  pair  of  mutually  counterpoised  filters,  washed  slightly 
with  water,  pressed  strongly  between  folds  of  blotting  paper,  dried 
at  100°  C.  and  weighed.  Some  of  the  precipitates  bear  washing 
fairly  well.  Most  of  them  begin  to  dissolve  as  soon  as  excess  of 
Mayer's  reagent  is  no  longer  present.  If  the  washing  is  continued, 
a  precipitate  begins  to  form  in  the  washings,  showing  that  the  water 
is  carrying  through  some  of  the  alkaloid,  the  precipitate  being  either 
decomposed  or  dissolved.  By  using  moderately  dilute  solutions, 
however,  and  washing  the  filters  rather  than  the  precipitate,  results 
were  obtained  which  are  believed  to  be  reasonably  near  the  truth. 
The  precipitates  were  analyzed  in  the  following  manner :  They 
were  dissolved  in  alcohol,  ammonium  sulphide  was  added  in  slight 
excess,  and  the  mercuric  sulphide  was  collected,  dried  and  weighed. 
The  solution  was  then  treated  with  a  drop  or  two  of  solution  of  ferric  sul- 
phate to  precipitate  the  excess  of  sulphur,  filtered,  and  the  iodine  esti- 
mated volumetrically  with  silver  nitrate.  In  a  few  instances  the  silver 
iodide  was  also  collected  and  weighed,  the  result  generally  coinciding 
with  that  obtained  by  titration,  although  in  some  cases  it  seemed  proba- 
ble from  the  discrepancy  in  weight  that  the ,  precipitate  contained 
chlorine  as  well  as  iodine. 
It  is  expected  that  the  color  of  the  precipitate  of  mercuric  sulphide 
will  be  black  when  an  excess  of  reagent  has  been  employed  to  produce 
it.  In  all  but  one  of  my  experiments  such  was  the  fact ;  in  the  ex- 
ceptional instance,  the  precipitate  remained  persistently  red,  a  bright 
brick-red,  like  native  cinnabar.  Which  of  the  alkaloids  it  was  that 
gave  this  anomalous  reaction,  I  cannot  now  remember,  but  there  is  a 
suggestion  in  the  observation  of  a  possible  new  method  of  preparing, 
vermilion. 
