10         METHOD  OF  PREPARING;  PROTIODIDE  OF  MERCURY. 
rections  in  the  book."  Of  this* I  had  some  doubts,  owing  in  part 
to  the  time  occupied  in  the  operation. 
I  therefore  concluded  that  the  calomel  and  iodide  of  potassium 
had  not  been  thoroughly  triturated  together,  and  that  decompo- 
sition had  not  fully  taken  place  before  the  addition  of  hot  water. 
I  am  confirmed  in  this  opinion,  as  another  quantity  prepared 
from  the  same  materials  and  by  the  same  person,  but  with  a 
longer  and  more  perfect  trituration,  gave  no  such  result,  but 
yielded  a  perfect  protiodide,  in  which  metallic  mercury  could 
not  be  distinguished  even  with  the  aid  of  a  microscope. 
I  think  the  same  opinion  will  hold  good  in  Mr.  Bullock's  case; 
that  from  the  large  quantity  of  materials  used,  and  the  great 
difficulty  of  reducing  the  iodide  of  potassium  to  a  powder  fine 
enough  for  each  particle  to  be  acted  upon  by  a  particle  of  calo- 
mel, is  a  great  deal  in  favor  of  my  theory,  that  double  decom- 
position had  not  fully  taken  place  prior  to  the  addition  of  hot 
water;  and  owing  to  the  large  quantity  of  iodide  of  potassium 
found  in  the  washings,  it  seems  to  me,  was  another  proof  that 
the  process  of  decomposition  was  arrested  by  the  too  early  ad- 
dition of  the  hot  water. 
The  metallic  mercury  I  account  for  as  follows :  A  portion  of 
the  calomel  having  parted  with  its  chlorine,  the  base  had  not 
had  time,  as  it  were,  to  combine  with  the  iodine  of  the  iodide  of 
potassium ;  the  mercurial  salt  in  solution,  I  presume,  was  a  por- 
tion of  the  protiodide  of  mercury  held  there  by  the  iodide  of 
potassium  ;  but  as  these  are  only  suppositions,  not  having  time 
to  look  into  the  matter  more  fully,  I  give  them  for  what  they  are 
worth. 
I  have  never  found  any  difficulty  in  making  the  protiodide 
of  mercury  according  to  M.  Boutigny's  process  in  small  quanti- 
ties, and  taking  care  to  use  a  great  deal  of  trituration ;  and  I 
doubt  much  whether  it  can  be  prepared  perfectly  in  large  quanti- 
ties, such  as  those  used  by  Mr.  Bullock,  which  would  require  a 
very  large  mortar  and  a  great  deal  of  labor.  All  the  forms  of 
M.  Boutigny  I  have  seen,  give  the  proportions  in  drachms, 
which  is  as  much,  I  think,  as  can  be  prepared  at  once. 
New  York,  Nov.  1,  1856 
