218      EFFFCTS  OF  SUNLIGHT  ON  SYRUPUS  FERRI  IODIDI. 
ON  THE  EFFECTS  OF  THE  SUN-LIGHT  ON  SYRUPUS  FERRI 
IODIDI. 
By  John  M.  Maisch. 
#  Several  months  since,  I  published  in  this  journal  the  results  of 
a  series  of  experiments  on  the  changes  of  syrup  of  iodide  of 
iron,  and  the  effect  of  light  on  it.  Since  then  I  have  made 
another  number  of  experiments  with  a  view  to  find  an  easy  way 
of  preserving  the  iodide  of  iron  in  a  watery  solution,  and  also 
to  ascertain  the  manner  in  which  sugar  acts  on  this  iodide  after 
its  change  by  the  oxygen  of  the  atmospheric  air. 
A  fresh  prepared  aqueous  solution,  kept  in  a  filled  and  well- 
corked  vessel,  rapidly  undergoes  a  change,  no  matter  whether 
it  had  been  kept  in  the  dark  or  was  exposed  to  the  direct  rays 
of  the  sun.  The  oxygen  of  the  air  which  has  been  absorbed 
during  filtration,  separates  the  iron  from  iodine  in  the  well  known 
way,  by  forming  under  the  aid  of  a  corresponding  quantity  of 
water,  sesquioxide  of  iron  and  hydriodic  acid,  which  again  de- 
composes, setting  some  iodine  free.  An  exposure  of  this  de- 
composed solution  to  the  sun  is  of  no  avail ;  but  after  sugar  has 
been  dissolved  in  it,  and  this  saccharated  solution  is  put  in  the 
sun-light,  it  at  first  becomes  colorless  and  afterwards  iissolves  the 
oxide  of  iron.  Repeated  experiments  with  the  same  results 
always  showed  the  presence  of  free  iodine  before  the  addition  of 
sugar,  as  I  fouud  it  likewise  in  the  syrup  which  had  undergone 
this  change.  But  after  the  aqueous  solution  had  been  kept  (in 
a  closely  stoppered  vial)  for  several  months,  sugar  and  sunlight 
did  not  produce  the  expected  effect  of  bleaching  and  dissolving  the 
separated  oxide  of  iron.  The  reason  of  this  is  doubtless  to  be 
looked  for  in  the  state  of  the  oxide,  which,  recently  precipitated, 
is  a  hydrate  easily  soluble  in  acids,  but  changes  to  a  crystalline 
state,  when  it  dissolves  with  difficulty  even  in  the  stronger  acids. 
The  more  completely,  therefore,  the  oxide  of  iron  has  become 
crystalline,  the  less  visible  will  be  the  influence  of  sugar  and  sun- 
light. A  syrup  which  has  stood  decomposed  with  its  precipitated 
oxide  of  iron  for  several  months,  may  become  lighter,  but  not 
colorless,  still  containing  free  iodine  in  solution  and  oxide  of  iron 
as  a  precipitate. 
As  it  was  interesting  to  know  in  what  chemical  way  the  sun- 
