216  Value  of  Certain  Salts  of  Iron,  etc.  {A^vTimf^ 
iodine  are  first  combined  with  metallic  iron,  in  the  usual  way  to  ob- 
tain the  proto-iodide  of  iron  ;  this  is  filtered,  and  63  grs.  (J  eq.)  of 
iodine  are  dissolved  into  it.  Then,  a  solution  of  201  grs.  (1  eq.)  of 
citric  acid  saturated  with  a  fixed  alkali,  such  as  potassa,  for  instance,, 
is  added  by  small  portions  to  the  sesqui-iodide  of  iron.  The  ferru- 
ginous solution  which  is  at  first  of  a  ruby  red  color  and  has  a  strong 
smell  of  iodine,  becomes  lighter  by  degrees,  till  as  the  last  drop  of 
citrate  is  added,  it  takes  a  bright  apple  green  color  ;  at  the  same  time,, 
all  smell  of  iodine,  all  taste  of  iron  have  disappeared  ;  the  solution 
strikes  no  color  on  starch  paper,  and  gives  no  precipitate  with  either 
tannin  or  ferrocyanide  of  potassium.  It  may  be  then  evaporated  at 
a  low  heat,  with  gentle  stirring  to  dryness,  when  it  gives  a  green  mass 
formed  of  very  small  acicular  crystals,  looking  somewhat  like  cauli- 
flowers. It  is  tasteless,  perfectly  stable,  unless  exposed  to  direct  sun- 
light, and  may  be  exhibited,  in  the  shape  of  syrup,  elixir,  solution., 
tincture,  pills,  etc.  The  dose  of  it  need  not  be  more  than  one-half  of 
that  of  the  proto-iodide  of  iron,  as  it  is  absorbed  much  more  readily. 
Chemically,  this  iodide  of  iron  seems  to  be  a  combination  in  which 
sesqui-iodide  of  iron  plays  the  part  of  an  acid  and  the  alkaline  citrate 
that  of  a  base  ;  but  the  subject  requires  further  investigations  before 
it  can  be  decided  with  complete  certitude. 
The  other  alkaline  citrates  may  be  used  instead  of  citrate  of  potas- 
sa ;  similar  combinations  may  also  be  obtained  with  the  alkaline  tar- 
trates, oxalates,  and  malates,  but  none  are  so  tasteless,  and  especially 
none  so  stable  as  the  one  just  mentioned. 
I  must  add  a  few  words  on  this  subject  which  is  a  most  important 
one,  for  the  same  remarks  may  be  applied  to  all  the  other  analogous 
iron  combinations,  pyrophosphate  included.  On  reading  the  above 
process,  some  may  think  that,  after  all,  the  product  is  only  a  mixture 
of  citrate  of  iron,  iodide  and  iodate  of  potassium.  But,  aside  of  the 
fact  that  the  different  ingredients  are  not  in  proportion  to  form  such 
combinations,  chemical  tests  show  that  such  is  not  the  case.  Citrate 
of  iron,  for  instance,  is  of  a  ruby  red  color  and  turns  immediately  ink 
black  on  the  addition  of  tannin,  while  tasteless  iodide  of  iron  is  bright 
green  and  is  not  colored  black  by  tannin,  but  only  turned  to  a  light 
purple  hue,  after  some  time.  Iodide  of  potassium  dissolves  iodine 
freely :  the  new  salt  dissolves  it  but  sparingly,  unless  when  in  a  con- 
centrated solution.  Iodate  of  potassium  is  colored  red  by  solutions, 
of  morphia  :  no  coloration  is  produced  by  them  in  solutions  of  the  new 
