230 
Calcium  Iodide. 
f  Am. .lour.  Phainon 
t      May,  1883. 
which  cannot  be  properly  filtered  through  paper  in  an  undiluted  con- 
dition. Its  destructive  action  upon  the  paper  results  in  soluble  colored 
products,  which  interfere  with  the  whiteness  of  the  dried  salt.  The 
affinity  of  calcium  iodide  for  water  is  so  great  that  when  a  very 
concentrated  solution  of  it  is  mixed  with  an  equally  strong  solution  of 
dipotassic  carbonate,  no  double  decomposition  occurs,  but  the  potassic 
carbonate  separates  as  a  gelatinous  magma.  No  calcium  carbonate 
results  until  more  water  is  added,  when  the  calcium  is  immediately 
thrown  down  as  white  carbonate. 
The  calcium  iodide  on  evaporation  of  its  solution  is  obtained  as  a 
white  or  colorless  crystalline  salt  containing  water.  The  solution  must 
be  concentrated  until  a  dense  pellicle  forms  over  the  surface.  The  fused 
mass  is  then  poured  on  a  smooth  surface  and  well-covered  to  prevent 
deliquescence.  On  cooling,  the  salt  is  readily  detached  in  large  frag- 
ments. These  may  then  be  broken  into  smaller  pieces  and  preserved 
in  well-stopped  bottles.  Large,  shallow  capsules  or  ordinary  dinner 
plates  with  bright  smooth  surfaces,  are  the  most  suitable  vessels  for 
cooling  the  fused  salt.  During  this  part  of  the  operation  it  is  essential 
that  moist  air  be  excluded  to  prevent  deliquescence.  For  this  reason 
the  salt  is  best  dried  under  a  bell-glass  over  sulphuric  acid. 
In  the  preparation  of  calcium  iodide  the  use  of  iron  filings  is  not 
admissible,  because  of  the  large  amount  and  the  peculiar  form  of  the 
carbon  contained  in  them.  In  this  instance,  a  yellow  organic  acid  is 
generated,  which  yields  colorless  ferrous  salts  and  orange  ferric  salts 
not  precipitable  by  calcium  carbonate,  but  decomposable  by  a  calcium 
hydrate.  The  resulting  calcium  salt  of  this  acid  is  also  orange  tinted, 
but  is  destroyed  on  fusion  of  the  iodide,  the  carbonaceous  residue  im- 
parting to  this  a  greyish,  unsightly  appearance.  Re-solution  of  the 
fused  mass  and  filtration  of  the  solution  now  produces  a  colorless  salt. 
Iron  wire  also  contains  some  carbon,  but  in  a  dinerent  state  of  combi- 
nation, so  that  none  of  the  peculiar  acid  is  produced.  With  its  use  the 
iron  is  wholly  precipitated  by  calcium  carbonate,  even  in  the  presence  of 
excess  of  iodine,  and  a  white  salt  is  directly  obtained  on  evaporation. 
The  contact  of  organic  matter  must,  however,  be  carefully  prevented 
in  the  manipulation,  and  the  filtration  of  a  too  concentrated  solutions, 
through  paper  must  be  avoided. 
From  these  considerations,  the  following  formula  is  derived : 
Iron  in  fine  wire,         ...  56  parts. 
Iodine,   381  " 
Calcium  carbonate,      .         .         .  150  *' 
Water  sufficient. 
