240 
PREPARATION  OF  IODIDE  OP  AMMONIUM. 
of  combination  at  all,  or  merely  in  intimate  mixture,  remains 
unascertained*. 
It  would  appear  that  during  that  remarkable  change  which 
has  resulted  in  the  formation  of  these  "  casts  "  of  minute  marine 
animals,  which  the  researches  of  Ehrenberg  and  the  late  Prof. 
Bailey  have  shown  these  green  grains  to  be,  the  silica  has  been 
deposited  in  the  cavity  of  the  shell  upon  or  during  the  decay  of 
the  animal ;  while  the  green  colored  matter,  consisting  of  iron, 
alumina,  potassa,  &c,  has  been  gradually  deposited  in  the  shell 
around  it  by  a  kind  of  petrifactive  process  during  the  removal 
of  its  carbonate  of  lime. — Proceed.  Amer.  Pharm.  Assoc.,  1863, 
ON  THE  PREPARATION  OF  IODIDE  OF  AMMONIUM.* 
By  Dr.  Jacobsen. 
The  author  dissolves  equivalent  weights  of  pure  iodide  of  po- 
tassium and  pure  sulphate  of  ammonia  in  the  smallest  possible 
quantity  of  boiling  distilled  water.  One  part  of  sulphate  of 
ammonia  will  require  about  one  and  one-third  of  its  weight, 
and  iodide  of  potassium  about  half  its  weight  of  boiling  water 
for  solution.  The  two  solutions  are  then  mixed  and  well  stirred. 
After  the  mixture  has  cooled,  water  containing  15  per  cent,  of 
alcohol  is  added,  and  the  whole  is  allowed  to  stand  twelve 
hours.  In  very  cold  weather  less  alcohol  will  suffice  to  separ- 
ate the  sulphate. of  potash  formed.  According  to  Schiff,f  100 
parts  of  water  and  10  parts  of  alcohol  at  15°  C.  only  dissolve 
3-9  parts  of  sulphate  of  potash. 
The  iodide  of  ammonium,  in  consequence  of  its  greater  solu- 
bility, remains  in  the  solution,  which  is  now  drained  from  the 
precipitated  sulphate  of  potash,  filtered,  and  evaporated  until  a 
pellicle  forms.  As  the  solution  is  very  concentrated,  the  evap- 
oration is  quickly  effected. 
After  the  crystals  of  iodide  of  ammonium  are  formed,  they 
are  drained  from  the  mother  liquor,  which,  together  with  the 
residue  of  sulphate  of  potash,  is  again  treated  with  dilute  alco- 
hol, and  the  liquor  evaporated  for  a  further  yield  of  sufficiently 
pure  iodide.  Care  must  be  taken  to  exclude  all  acid  vapors 
from  the  chamber  in  which  the  evaporation  is  carried  on ;  and 
it  is  well  to  add  to  the  solution,  from  time  to  time,  a  few  drops 
of  ammoniated  alcohol. — Lond.  Chem.  News,  April  9,  1864. 
*  News  Jahrbuch.  fur  Pharmacie,  bd.  cxx.  vii.,  s.  256.  ' 
f  Ann.  der  Chem.  und  Pharm.,  bd.  cxviii.,  s.  365. 
