i;f874RM'}  Preparation  of  Biniodide  of  Mercury,  etc.  17 
Am.  Jour.  Pharm. 
Feb 
uct  be  obtained  (a)  of  the  best  quality ;  (6)  at  the  lowest  cost :  (c) 
with  the  least  trouble.  As  a  general  rule,  the  relative  importance  of 
these  conditions  is  indicated  by  the  order  in  which  they  are  given  ; 
quality  is,  or  should  be,  the  great  essential,  while  cost  and  conveni- 
ence are  of  secondary  consequence.  Too  often,  however,  this  order 
is  reversed,  and  all  considerations  are  made  subordinate  to  that  of 
cost;  but,  in  no  case,  can  this  be  justifiable;  it  is  only  when  the  mat- 
ter of  quality  is  satisfactorily  settled  that  we  are  at  liberty  to  decide 
in  favor  of  that  process  which  promises  to  be  the  most  economical. 
The  question  of  economy  is,  however,  to  the  pharmacist,  a  most  im- 
portant one,  and,  in  cases  of  scarcity  of  material  or  high  prices,  merits 
his  best  attention. 
A  case  in  point  is  that  of  the  red  iodide  of  mercury — a  compound 
which  is  almost  invariably  prepared  by  the  pharmacist.  The  recent 
inflation  in  the  price  of  iodide  of  potassium,  and  the  high  figure  which 
it  at  present  maintains,  demand  the  utmost  economy  in  its  use.  In 
view  of  this  it  may  be  opportune  to  review  the  various  processes  which 
have  been  devised  for  the  preparation  of  the  biniodide  of  mercury,  so 
that  we  may  be  able  to  obtain  the  best  results  with  the  least  possible 
expenditure  of  materials. 
The  first  process  which  might  be  noticed  is  that  in  which  the  binio- 
dide is  formed  by  a  direct  union  of  the  elements  composing  it.  Mer- 
cury and  iodide  are  triturated,  or  agitated  together,  a  little  alcohol 
being  added  to  control  the  reaction.  In  inexperienced  hands  this 
process  yields  an  imperfect  product ;  is  exceedingly  wasteful  and 
troublesome,  and  may  be  so  dismissed. 
A  better  process  is  that  of  the  British  Pharmacopoeia,  4  parts  of 
perchloride  of  mercury,  dissolved  in  60  parts  of  boiling  water,  are 
mixed  with  5  parts  of  iodide  of  potassium,  in  20  parts  of  boiling  water. 
The  iodide  is,  theoretically  and  practically,  one-tenth  of  one  part  in 
excess  of  that  actually  required  for  the  decomposition.  Its  object  is 
to  prevent  contamination  of  the  product  with  the  mercuric  salt.  This 
excess  appears  useless,  first,  because,  with  any  ordinary  care,  the 
operator  can  ascertain  the  moment  the  decomposition  is  complete ; 
and,  again,  if  any  slight  excess  of  mercuric  salt  happened  to  be  pre- 
sent, it  would  certainly  be  removed  in  the  subsequent  copious  wash- 
ings to  which  the  biniodide  is  subjected.  This  excess  is  not  only 
wasteful  as  far  as  the  iodide  of  potassium  is  concerned,  but  of  the 
biniodide  also,  as  the  latter  salt  is  soluble  in  the  former.    The  use  of 
