24 
LIQUOR  FERRI  IODIDI. 
metalloid  is  combined  with  the  metal ;  and  to  avoid  the  eleva- 
tion of  temperature  during  the  chemical  combination,  the  bottle 
must  be  shaken  under  a  stream  of  cold  water,  or  in  a  tub  of  ice 
water. 
When  all  of  the  iodine  is  combined  with  the  iron,  which  re- 
quires only  half  an  hour,  the  light  green  solution  is  filtered,  and 
the  filter  washed  with  a  sufficient  quantity  of  water  to  make  the 
liquid  measure  12  oz.  fluid.  To  this  the  sugar  is  added,  the 
whole  raised  to  the  boiling  point,  and  strained.  When  cold,  20 
oz.  fluid  must  be  completed  with  some  water,  then  the  liquor  is 
put  in  a  ibj.  or  4  oz.  bottle,  according  to  the  sale.  The  filtration 
requires  no  more  than  ordinary  care,  no  decomposition  takes 
place,  and  none  of  the  salt  is  left  on  the  filter,  on  which  remains 
only  a  small  portion  of  the  excess  of  the  metallic  iron. 
The  liquor  thus  made  can  be  kept  free  of  decomposition,  in 
filled  bottles,  either  in  the  light  or  in  the  dark.  When  the  bottles 
are  not  full,  if  kept  in  the  dark,  the  liquor,  after  a  while,  be- 
comes slightly  yellowish  ;  but  if  exposed  in  a  warm  place  or  to 
the  rays  of  the  sun,  its  beautiful  light  green  color  is  restored, 
and  invariably  maintained  if  kept  so  long  enough. 
When  liquor  ferri  iodidi  is  undergoing  decomposition,  I  have 
ascertained  that  the  decomposition  stops  at  a  certain  point,  and 
goes  no  farther,  even  when  placed  in  an  evaporating  dish,  simply 
covered  with  a  piece  of  paper,  and  left  in  the  dark.  Why  is 
this  ? 
Again,  when  this  same  preparation,  with  or  without  an  excess 
of  iodine  is  exposed  a  certain  length  of  time  to  the  heat  or  to 
the  rays  of  the  sun,  it  permanently  keeps  its  light  greenish  color. 
Why  is  this  also  ? 
At  present  I  am  not  fully  prepared  to  answer  these  two  ques- 
tions, but  I  may  take  another  opportunity  for  doing  so.  How- 
ever, I  may  be  allowed  to  say  here,  that  the  old  theory  of  the 
decomposition  of  iodide  of  iron,  first  into  protoxide  of  iron  and 
iodohydric  acid  by  the  decomposition  of  water,  and  afterwards 
the  transformation  of  the  proto  into  the  sesquioxide  by  the 
oxygen  of  the  air,  cannot  be  admitted  here,  except  perhaps  when 
the  iodide  of  iron  is  in  a  purely  aqueous  solution.  But  grant- 
ing the  correctness  of  the  theory,  we  would  ask  why  decompo- 
sition does  not  continue  indefinitely  in  saccharine  solutions  of 
