340 
ON  HYDRARGYRI  IODIDUM  VIRIDE,  B.  P. 
iodide,  and  the  mercuric  iodide.  The  first,  as  I  have  already 
mentioned,  is  stated  to  be  green,  dark  green,  or  yellowish-green ; 
the  second  yellow,  and  the  third  red.  Three  processes  are 
given  for  the  production  of  mercurous  iodide.  The  first  is  by 
direct  combination  of  mercury  and  iodine.  It  is  the  method  of 
the  Pharmacopoeia  which  I  have  examined  with  the  result  stated. 
The  second  is  to  decompose  calomel  with  iodide  of  potassium. 
In  the  third  process  mercurous  acetate  is  substituted  for  calomel. 
The  second  of  these  methods  is  stated  to  yield  "pure  green  " 
mercurous  iodide.  As  I  had  entirely  failed  to  obtain  such  a 
body  by  direct  combination,  I  made  several  careful  experiments 
with  this  process  of  double  decomposition.  235-5  grs.*  of  calo- 
mel were  triturated  with  166  grs.*  of  iodide  of  potassium  previ- 
ously dissolved  in  a  little  water.  The  mixture  was  allowed  to 
remain  for  twenty-four  hours  and  then  filtered,  the  precipitate 
washed  and  dried.  The  product  was  of  a  fine  dark  green  color, 
and  entirely  different  from  any  iodide  I  had  previously  obtained. 
Upon  testing  it,  however,  I  found  it  to  contain  a  large  quantity 
of  undecomposed  calomel.  Its  weight  was  also  much  less  than 
theory  would  indicate.  By  analysis  the  following  numbers  were 
obtained  : — 
Calomel,  41-7 
Mercurous  Iodide,  ....  35*3 
Mercury,     ,  23*0 
100-0 
Gmelin  states  that  the  ingredients  must  be  used  in  exactly 
equivalent  portions,  as  any  excess  of  iodide  of  potassium  would 
separate  metallic  mercury.  This  would  probably  occur  in  accor- 
dance with  the  equation  : — 
2HgI+KI=HgKI3+Hg. 
Soluble  salt. 
But  although  I  repeated  the  experiment  several  times,  weigh- 
ing the  ingredients  accurately,  and  digesting  them  together  for 
different  periods,  in  no  case  could  I  obtain  anything  like  com- 
*Equivalent  quantities. 
