Amju0nuer,'i89h8arm'}    Atropine  Pericdides  and  lodomer curates.  299 
In  the  gravimetric  estimation  of  total  iodine,  0-2031  gramme  gave 
0-30035  silver  iodide. 
Calculated  for 
C17H23N03.HI.I8.  Found. 
Total  iodine   7974  79*9° 
Analyses  of  the  Double  Salts  of  Atropine  Hydriodide  and  Mercuric 
Iodide:  0-2632  gramme  of  the  monoatropine  hydriodide  mercuric 
iodide  gave  0-0699  gramme  mercuric  sulphide,  and  0  30445  gramme 
of  the  substance  gave  0  24785  gramme  silver  iodide. 
Calculated  for 
Atrop.  HI.Hglo.  Fouud. 
Mercury  23-03  22*89 
Iodine   43  7  4  43  "98 
Of  the  diatropinehydriodide  mercufic  iodide,  0-1798  gramme  gave 
o  032  gramme  mercuric  sulphide,  and  0  257  gramme  of  the  substance 
gave  0-18885  gramme  silver  iodide. 
Calculated  for 
(Atrop.  HI)2.HgI2.  Found. 
Mercury    .  .    15-58  15*34 
Iodine  39'46  397o 
III.  ATROPINE  ESTIMATION  AS  PERIODIDE. 
The  formation  of  atropine  enneaiodide  under  the  conditions 
described  above  affords  a  convenient  method  for  estimating  the 
strength  of  atropine  solutions  by  means  of  a  standard  solution  of 
iodine  and  titrating  back  with  a  standard  solution  of  sodium  thio- 
sulphate.  The  way  to  operate  is  as  follows  :  The  atropine  solution, 
whose  strength  is  approximately  determined  by  a  preliminary  experi- 
ment, operating  in  the  way  described  below,  is  diluted  with  water 
so  as  to  contain  at  most  four-tenths  to  five-tenths  per  cent,  of  the 
alkaloid,  and  in  so  doing,  the  solution  is  made  up  to  a  given  volume. 
Twenty  or  thirty  cubic  centimeters  of  a  decinormal  iodine  solution 
are  now  put  into  a  measuring  flask  holding  100  c.c,  diluted  with  a 
little  water,  and  acidulated  with  a  few  drops  of  diluted  sulphuric 
acid ;  the  atropine  solution  is  now  run  in  from  a  burette  slowly,  and 
in  small  portions  at  a  time,  shaking  the  flask  thoroughly  after  each 
addition  and  observing  whether  the  supernatant  liquid  commences 
to  clear  up.  If  not,  a  little  more  of  the  atropine  solution  is  added, 
and  the  mixture  again  shaken  for  a  minute  or  two.  In  this  way 
the  addition  of  atropine  is  slowly  continued  till  after  a  few  shakings 
the  supernatant  liquor  commences  to  become  transparent,  still  hav- 
