174 
ON  LIQUOR  FERRI  IODIDI. 
acid,  qualitatively  and  quantitatively.  It  showed  no  formation 
of  iodine  by  the  addition  of  hydrochloric  acid,  but  some  was 
set  free  by  sulphuric  acid.  The  first  test  is  conclusive  as  to  the 
absence  of  iodic  acid,the  latter  reaction  takes  place  with  all  iodides, 
whether  an  iodate  be  present  or  not.  I  determined  the  quanti- 
ty of  iodine  present  by  oxidation  with  a  graduated  solution  of 
hypochlorite  of  soda.  The  amount  found  corresponded  precise- 
ly with  the  quantity  of  the  silver  contained  in  the  precipitate. 
I  conclude  from  this  absence  of  iodic  in  the  decolorized  liquor 
prepared  from  pure  iodine,  that  the  sample  examined  by  my  friend 
Maisch,  had  been  made  from  iodine  containing  a  small  portion 
of  chlorine.  This  is  a  very  common  admixture,  and  very  few 
samples  of  iodine  will  be  found,  which,  when  water  is  poured 
on,  do  not  at  once  give  a  brownish  solution,  owing  to  the  pre- 
sence of  chloride  of  iodine. 
The  change  which  takes  place  on  exposing  Liquor  Ferri  Iodi- 
di  to  the  air  is  owing  to  the  action  of  atmospheric  oxygen  on  the 
protoxide  in  solution,  precipitating  a  basic  hydriodate  of  the 
sesqui- oxide  of  iron,  and  setting  free  some  hydriodic  acid, 
which  in  connection  with  the  acid  of  the  solution,  partly  decom- 
poses again  some  of  the  sesqui-oxide,  forming  protoiodide  and 
free  iodine.  When  this  brown  liquor  is  heated  in  a  porcelain 
dish,  its  color  becomes  lighter  in  the  measure  as  the  free  acid 
decomposes  the  sesqui-oxide,  and  the  iodine  is  dissipated.  It 
turns  colorless  if  hydriodic  acid  or  iodine  be  added  while  boiling. 
It  may  be  evaporated  to  dryness  in  a  salt  bath,  allowing  a  slight  ex- 
cess of  iodine  to  be  present  during  the  ivhole  of  the  evaporation,  and 
it  will  again  be  perfectly  soluble  in  water,  yielding  a  green  precipi- 
tate with  potassa.  During  the  heating,  most  if  not  all  the  cane 
sugar  of  the  solution  is  converted  into  glucose.  A  similar  re- 
action takes  place  when  the  stoppered  bottle  containing  the 
brown  liquor  is  exposed  to  the  direct  rays  of  the  sun.  Here 
the  formation  of  glucose  by  hydriodic  acid  takes  place,  though 
not  as  complete  as  in  the  open  dish ;  but  it  super-induces  the 
action  of  the  acid  on  the  suspended  sesqui-oxide,  which  is  thereby 
completely  converted  into  protoxide,  its  oxygen  and  the  hydro- 
gen of  the  acid  being  taken  up  by  the  sugar. 
That  sesquioxide  of  iron  is  dissolved  by  hydriodic  acid  and 
converted  into  protoxide  by  heating  the  solution,  is  an  old  fact, 
and  a  number  of  very  delicate  volumetric  methods  are  founded 
