ON  LIQUOR  FERRI  IODIDI. 
177 
iodine,  and  then  the  solution  of  arsenite  slowly,  and  towards  the 
end  drop  by  drop,  until  the  blue  color  of  the  starch  all  at  once 
disappears.  The  difference  in  the  weight  of  arsenite  of  potassa 
is  then  an  accurate  measure  of  the  quantity  of  pure  iodine. 
One  hundred  grains  of  the  solution  are  equivalent  to  1-269 
grains  of  pure  iodine. 
The  solution  of  hyposulphite  of  soda  is  prepared  by  dissolving 
350  grains  of  the  salt  in  water,  and  dilute  to  one  quart  or  two 
pounds  avoirdupois.  The  iodine,  when  to  be  examined  by  this 
test,  must  first  be  dissolved  in  iodide  of  potassium,  after  which 
the  reaction  goes  on  as  with  arsenite  of  potassa ;  one  hundred 
grains  being  equivalent  to  1-269  grains  of  pure  iodine.  These 
solutions  are  very  dilute,  and  by  the  comparative  largeness  of 
the  dose  needed  for  small  quantities  of  iodine,  a  great  margin  is 
left.  The  above  solution  of  arsenite  serves  as  a  measure  for 
hypochlorite  of  soda,  chlorine  and  chloride  of  lime.  It  is  added 
to  a  known  quantity  of  these  substances,  until  a  drop  of  the 
mixture  ceases  to  produce  a  blue  spot  on  white  paper  sized  with 
iodide  of  potassium  and  starch. 
Regarding  the  qualitative  tests  of  iodide  of  potassium  treated 
on  in  the  Dispensatory,  it  must  be  added  that  the  solution  of 
the  salt  must  be  dilute  when  tested  with  sulphuric  acid  and 
starch ;  for  strong  solutions  disengage  the  iodine  at  once.  The 
test  described  for  chlorine  contained  in  iodine  is  equally  as  well 
applied  to  iodide  of  potassium.  The  persalt  of  iron  must  be 
perfectly  free  from  chlorine.  The  resulting  solution  of  iron 
treated  with  chlorine  water  and  ether  shows  bromine,  if  present. 
In  Personne's  test  for  bromide,  the  sulphurous  acid  is  advan- 
tageously replaced  by  hyposulphite  of  soda.  Iodate  of  potassa 
is  present  when,  on  the  addition  of  pure  hydrochloric  acid,  free 
iodine  makes  its  appearance. 
The  quantitative  test  of  Marozeau,  as  described  by  Mr.  Maisch 
some  years  ago,  is  sufficiently  accurate  for  the  purposes  of  the 
pharmaceutist.  The  quantity  of  iodate  in  a  sample  is  found  by 
adding  some  hydrochloric  acid,  and  determining  the  quantity  of 
iodine  set  free  by  the  solution  of  hyposulphite  of  soda,  described 
above.  For  each  six  equivalents,  or  7-6  (seven  x60)  parts  of  iodine 
found,  put  2-14  parts  of  iodate  of  potassa. — Proc.  Am.  Pharm. 
Assoc.,  1859. 
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