Am  Jour.  Pharm.  1 
May,  1883.  j 
Calcium  Iodide. 
229 
As  there  are  always  new  medicinal  agents  coming  into  use  which  are 
not  often  found  in  the  market  until  the  demand  becomes  quite  general, 
the  pharmacist  is  occasionally  called  upon  to  exercise  the  primitive 
function  of  preparing  compounds  obtainable  in  no  other  way.  For 
such  and  similar  cases  only,  the  Pharmacopoeia  gives  processes,  in  con- 
nection with  those  that  are  pre-eminently  pharmacopoeial.  These  are, 
however,  rapidly  improved  in  most  cases,  so  that  the  early  official 
method  is  not  always  the  best  after  a  ten  years'  period  of  general  pro- 
Stress. 
Calcium  iodide  is  one  of  those  compounds  occasionally  called  for, 
which  is  not  generally  kept  nor  very  easily  prepared  in  a  proper  form. 
When  caustic  lime  is  triturated  with  iodine,  a  peculiar  black  combina- 
tion is  obtained  in  which  chemical  union  of  some  kind  is  exerted. 
Similar  compounds  are  produced  when  dry  iodides  are  mixed  with 
iodine  in  a  like  manner.  Some  of  these  bodies  are  soluble  in  alcohol, 
and  then  yield  crystals  of  definite  superiodide  even  of  the  monad 
metals.  Water  decomposes  them,  however,  with  the  liberation  of 
iodine.  On  boiling  the  black  calcium  oxide  and  iodine  compound  with 
water,  a  colorless  solution  of  calcium  iodide  and  iodate  is  obtained, 
whilst  the  excess  of  lime  remains  as  hydrate.  There  is  no  convenient 
way  of  separating  these  salts,  neither  is  the  reduction  of  the  attendant 
iodate  practicable.  Hence  this  process  does  not  answer  for  the  prepar- 
ation of  calcium  iodide. 
Calcium  iodide  may  be  prepared  by  dissolving  calcium  hydrate,  or 
better,  carbonate  in  iodhydric  acid.  The  difficulty  in  this  case  is  the 
preparation  of  the  acid  by  a  practical  and  convenient  method,  which  so 
far  has  not  been  found.  The  usual  process  for  preparing  calcium  iodide 
consists  in  decomposing  ferrous  iodide  or  ferric  iodide  with  calcium 
hydrate.  In  the  first  instance  the  iron  is  precipitated  as  ferrous  hydrate, 
and  in  the  second  as  ferric  oxy-hydrate.  Both  precipitates  are  exces- 
sively bulky,  and  require  much  washing  to  secure  all  of  the  generated 
calcium  iodide.  A  correspondingly  large  volume  of  water  will  then 
have  to  be  evaporated. 
The  process  which  embodies  the  most  advantage,  consists  in  decom- 
posing ferric  iodide  with  calcium  carbonate.  In  this  case  the  iron  is 
precipitated  as  the  compact  nongelatinous  ferric  hydrocarbonate,  accord- 
ing to  the  following  reaction  : 
2  (Fel3)  +  3  (CaC03)  +  2  (OH,)  =  3  (Cal,) + Fe,  CO,  (OH),  +  2  (CO,). 
A  very  concentrated  solution  of  calcium  iodide  is  thus  obtained, 
