250  On  the  Syrup  of  Ferrous  Iodide. 
only  by  taking  equivalent  proportions  of  iodine  and  iron  that  HI  will 
escape.  The  fresh  solution  of  ferrous  iodide,  even  when  shaken  with 
pulverized  iron,  turns  blue  litmus  paper  red,  not  indicating  free  HI,  but 
merely  the  characteristic  reaction  of  the  iron  groupe. 
My  researches  on  this  subject  were  made  in  the  following  way  :  10 
grams  of  dry  iodine,  2,  2  grams  of  iron  filings,  and  50  grams  of  water 
were  put  in  a  flask,  connected  by  a  bent  glass  tube  with  a  receiver  con- 
taining a  small  quantity  of  water  ;  the  flask  was  exposed  to  a  gentle 
heat  until  all  the  iodine  was  combined.  The  water  in  the  receiver  was 
found  to  contain  HI  equal  to  0*025  grams  of  iodine.  In  the  flask  re- 
mained a  brown  liquid,  yielding,  by  filtering,  a  greenish  solution  of  fer- 
rous iodide,  and  leaving  on  the  filter  ferric  oxide.  The  solution  was 
tested  and  found  to  contain  9*975  grams  of  iodine.  The  process  re- 
peated with  a  surplus  of  iron  gave  no  HI,  but  by  titre  the  full  amount 
of  iodine  taken. 
A  third  experiment  was  made  by  heating  10  grams  of  iodine,  5  grams 
of  iron  filings,  and  20  grams  of  water  in  the  same  apparatus  ;  the  re- 
maining surplus  of  iron,  well  washed,  was  dissolved  in  diluted  sulphuric 
acid,  passing  a  slow  stream  of  carbon  dioxide  in  the  meantime  through 
the  flask.  The  solution  of  ferrous  and  ferric  sulphate,  tested  volume- 
trically  with  potassium  permanganate,  gave  the  quantity  of  ferric  oxide, 
and  this  the  equivalent  HI,  which  was  generated  and  decomposed  again 
during  the  process  equal  to  0*075  grams. 
My  volumetric  tests  were  made  by  heating  10  to  15  c.c.  of  the 
liquid  ferrous  iodide  with  4  to  5  grams  of  dry  ferric  chloride.  The 
iodine  evolved  was  led  in  a  solution  of  potassium,  iodide,  and  this 
was  tested  with  a  volumetric  solution  of  sodium  hyposulphite.  The 
liquid  in  the  flask  containing  the  iron  salts  was  immediately  diluted  with 
cold  distilled  water  and  tested  with  a  volumetric  solution  of  potassium 
permanganate.  As  i  equivalent  of  ferric  chloride  and  i  of  iron  form 
3  equivalents  of  ferrous  chloride,  only  one-third  of  the  iron  found  was 
contained  in  the  liquid  ferrous  iodide. 
These  results  differ  entirely  from  Mr.  Mayer's  experiments,  as  he 
could  not  find,  in  a  single  instance,  the  liquid  ferrous  iodide  to  contain 
the  full  amount  of  iron  corresponding  to  the  quantity  of  iodine  em- 
ployed. The  deficiency  is  only  explainable  by  the  impurities  of  the 
iodine,  especially  its  moisture,  but  where  allowance  is  made  for  these, 
the  amount  of  iron  in  the  liquid  will  correspond  equivalently  with  the 
iodine  employed. 
