ON  HYDRARGYRI  IODIDUM  VIRIDE,  B.  P. 
341 
plete  decomposition.  The  first  portion  of  mercurous  iodide 
formed  was  apparently  decomposed  by  the  remainder  of  the 
iodide  of  potassium  in  preference  to  the  residual  calomel. 
The  results  of  these  experiments  were  consequently  confirma- 
tory of  those  previously  obtained,  and  contributed  to  show  that 
the  green  color  was  really  due  to  a  mixture  of  mercurous  iodide 
and  metallic  mercury. 
I  then  resorted  to  the  last  process  given  by  Gmelin,  namely, 
the  reaction  of  iodide  of  potassium  on  mercurous  acetate. 
Equivalent  quantities  of  crystallized  mercurous  acetate  and 
iodides  of  potassium  were  triturated  with  water.  The  first  effect 
was  the  production  of  a  nearly  black  precipitate,  which  grad- 
ually became  green,  and,  after  digesting  a  clay  or  two,  passed 
to  a  light  yellowish  green.  The  appearance  of  this  precipitate 
was  again  different  to  that  of  either  of  the  other  iodides  I  had 
prepared.  Upon  testing  it,  I  found  it  to  contain  a  considerable 
quantity  of  undecomposed  mercurous  acetate ;  consequently 
free  metallic  mercury  was  present  in  it. 
The  imperfect  decomposition  of  the  calomel  and  mercurous 
acetate  I  thought  possibly  arose  from  employing  them  in  the  un- 
dissolved condition.  Of  course  calomel  could  not  be  dissolved, 
but  mercurous  acetate  is,  to  a  certain  extent,  soluble.  We  can- 
not employ  hot  water  for  the  purpose  without  decomposing  a 
portion  of  the  acetate,  and  converting  it  into  a  mercuric  salt.  I 
therefore  prepared  a  cold  aqueous  solution  of  the  mercurous 
acetate,  and  tried  the  effect  of  mixing  it  with  a  very  dilute  solu- 
tion of  iodide  of  potassium.  Taking  care  to  keep  the  acetate  in 
slight  excess,  I  succeeded  in  obtaining  a  pure  yellow  precipitate, 
but,  owing  to  the  very  slight  solubility  of  mercurous  acetate,  the 
quantity  of  precipitate  I  obtained  was  so  small  that  I  did  not 
submit  it  to  analysis,  and  am  therefore  unable  to  say  whether  it 
was  pure  mercurous  iodide  or  the  mercuroso-mercuric  iodide  of 
Gmelin. 
This  latter  compound  I  have  not  yet  studied  in  comparison 
with  the  yellow  mercurous  iodide,  but  I  am  making  a  few  ex- 
periments for  that  purpose. 
It  results,  then,  from  what  I  have  stated,  that  by  none  of  the 
processes  indicated  could  I  succeed  in  obtaining  pure  mercurous 
