METHOD  OF  PREPARING  PROTIODIDE  OF  MERCURY.  517 
REMARKS  ON  BOUTIGNY' S  METHOD  OF  PREPARING 
PROTIODIDE  OF  MERCURY, 
By  Charles  Bullock. 
The  Pharmacopoeia  of  the  United  States  directs  proto-iodide 
of  mercury  to  be  prepared  by  direct  combination  of  its  elements. 
When  thus  prepared,  it  soon  loses  its  original  green  hue.  passing 
to  that  of  an  ochry  yellow.  This  change  occurs  equally  when 
the  salt  is  exposed  to  light,  or  when  protected  from  it.  Whether 
the  chemical  or  therapeutical  character  of  the  salt  is  affected  by 
this  change  I  have  not  been  able  to  determine.  It  has  been  our 
custom  not  to  dispense  it  after  it  assumed  the  yellow  tinge.  In 
order  to  obtain  a  proto-iodide  which  would  not  be  liable  to  this 
change,  I  was  induced  to  try  the  formula  recommended  by  M. 
Boutigny,  as  described  in  the  8th  vol.  of  this  Journal,  p.  326. 
Its  preparation  is  here  recommended  by  double  decomposition 
between  iodide  of  potassium  and  calomel.  A  specimen  made 
after  this  process  retained  its  original  green  hue  for  a  long  time. 
Pleased  with  the  result,  I  essayed  its  manufacture  on  a  larger 
scale,  when  some  unexpected  results  were  obtained.  Fifteen 
ounces  of  iodide  of  potassium  in  powder,  and  twenty-one  and 
three  eighth  ounces  of  calomel,  were  used.  These  are  the  pro- 
portions of  M.  Boutigny,  and  are  nearly  those  of  the  atomic 
weights  of  the  two  salts.  The  iodide  of  potassium  and  calomel 
were  rubbed  together.  On  the  addition  of  hot  water,  large 
globules  of  mercury  made  their  appearance.  The  water  decanted 
from  the  proto-iodide  was  examined,  and  found  to  contain  mer- 
cury in  solution.  A  drop  placed  on  light  copper  foil  did  not 
give  a  mercurial  stain  till  a  fragment  of  iodide  of  potassium  was 
added.  Supposing  some  biniodide  of  mercury  might  have  been 
formed  during  the  process,  and  dissolved  by  the  chloride  of 
potassium  present,  asmall  quantity  was  allowed  to  evaporate  in  a 
watch  glass,  no  bin-iodide  was  deposited,  but  crystals  resembling 
iodo-hydrargyrate  of  potassium.  A  solution  of  iodide  of  potas- 
sium added  to  the  mother  water  produced  no  change,  while  a  so- 
lution of  bi-chloride  of  mercury  produced  a  copious  red  precipitate. 
In  this  way  I  obtained  six  and  one-fourth  ounces  of  bin-iodide  of 
mercury  from  the  washings. 
