296         Atropine  Per  iodides  and  Todomer curates.  {AmA™im&rm' 
The  enneaiodide,  obtained  as  described,  being  unstable  while 
moist  and  when  removed  from  its  mother-liquor,  the  precipitate  has 
to  be  collected  quickly  by  means  of  a  pump,  washed  a  few  times 
with  cold  water  and  dried  first  on  porous  plates  and  then  in  vacuum 
over  sulphuric  acid.  As  thus  obtained  it  is  a  very  dark  brown 
almost  black  powder,  quite  permanent  in  dry  air  and  has  only  a 
slight  odor  of  iodine.  It  is  very  difficultly  soluble  in  ether,  chloro- 
form, benzene  or  carbon  disulphide,  but  is  soluble  in  alcohol,  very 
freely  when  hot.  In  cold  water  it  is  insoluble  ;  hot  water  decom- 
poses it  quickly ;  it  is  also  decomposed  by  concentrated  solutions  of 
potassium  iodide.  At  90°  C.  it  commences  to  give  up  iodine  vapors 
and  at  140°  C.  melts  to  a  dark  liquid. 
To  obtain  it  in  crystalline  form  it  is  first  washed  with  a  little  cold 
alcohol  to  remove  traces  of  free  iodine  and  then  dissolved  in  warm 
alcohol.  On  cooling  it  crystallizes  out  in  dark-green  prisms  and 
leaflets,  having  the  same  properties  as  the  non-crystallized  body. 
In  this  enneaiodide  one-ninth  of  the  total  iodine  is  firmly  com- 
bined just  as  in  normal  hydriodides,  while  eight-ninths  is  easily 
removed  by  reducing  agents,  such  as  sulphur  dioxide  and  sodium 
thiosulphate.  The  compound  therefore  may  be  considered  an  atro- 
pine hydriodide  octaiodide. 
The  additive  iodine  we  estimated  volumetrically  and  the  total 
iodine  both  gravimetrically  and  volumetrically. 
To  estimate  the  additive  iodine  a  small  quantity  of  the  enneaiodide 
is  dissolved  in  very  little  alcohol,  an  excess  of  a  standardized  solu- 
tion of  sodium  thiosulphate  added  and  the  excess  titrated  back  with 
a  standard  solution  of  iodine,  using  starch  as  the  indicator. 
For  total  iodine  the  substance  is  covered  with  an  excess  of  pow- 
dered metallic  zinc  and  some  water  and  then  boiled  gently  for  ten 
or  fifteen  minutes,  taking  care  to  prevent  loss  by  spurting  :  the  mix- 
ture is  then  thrown  upon  a  filter,  and  the  containing  flask  and  the 
filter  thoroughly  washed  with  hot  water.  The  iodine  in  the  zinc 
iodide  thus  formed  can  either  be  estimated  by  precipitation  with 
silver  nitrate  and  nitric  acid  and  weighing  as  silver  iodide,  or  it  is 
precipitated  with  an  excess  of  a  standardized  solution  of  silver  nitrate 
and  the  excess  titrated  back  with  a  standard  solution  of  ammonium 
thiocyanate,  using  ferric  nitrate  as  indicator. 
Having  obtained  the  enneaiodide  of  atropine  it  was  natural  to 
suppose  the  existence  of  a  heptaiodide,  with  probability  of  a  com- 
