224 
INCOMPATIBILITIES  OF  IODIDE  OP  POTASSIUM. 
as  no  evolution  of  hydrogen  is  apparent.  The  same  occurs  more 
slowly  without  heat.  In  every  instance,  a  drop  of  the  above  so- 
lution put  on  bright  copper,  instantly  precipitates  mercury  and 
causes  a  silvery  stain. 
Now  it  is  well  known  that  iodide  of  potassium  proves  useful  in 
cases  where  mercurials  have  been  taken  to  abuse ;  do  not  the 
reactions  above  detailed  show  that  in  every  ordinary  form  of  mer- 
curial, this  salt  exerts  a  solvent  power,  which,  in  connection  with 
its  ready  elimination  by  the  bladder,  may  prove  efficacious  by 
acting  as  a  collector  of  the  metal  in  whatever  form  of  combination 
it  may  exist  in  the  system  ?  Do  they  not  suggest  that  physicians 
should  observe  due  care  in  the  use  of  calomel,  protiodide  of 
mercury  and  blue  mass,  in  connection  with  iodide  of  potassium, 
as  the  iodo-hydrargyrate  of  potassium,  which  is  formed  by  this 
reaction,  exhibits  its  peculiar  effects  in  doses  of  one-twelfth  of  a 
grain  ? 
It  would  probably  repay  the  time  occupied  in  the  observations, 
if  some  of  our  medical  friends  would  watch  the  effect  on  the  com- 
position of  the  urine  in  cases  where  iodide  of  potassium  was  being 
administered,  as  in  old  syphilitic  cases,  where  mercury  had  been 
used  to  excess. 
Before  concluding,  it  is  proper  to  state  that  my  attention 
was  directed  to  the  subject  by  the  statements  of  Mr.  Morgan 
on  the  use  of  iodide  of  potassium  as  a  test  of  mercury,  (see  Am. 
Jour,  of  Pharm.,  xxiv.  pp.  177.)  This  test  is  admirably  calcu- 
lated to  discover  the  presence  of  mercury  in  any  form  in  a  medi- 
cine, as  in  pills,  powders  and  mixtures;  and  especially  for 
demonstrating  the  presence  of  the  metal  in  those  vegetable  quack 
pills  which  sometimes  act  so  much  like  the  mercurial  purgatives. 
All  that  is  necessary  is  to  take  a  penny,  dip  it  in  nitric  acid 
to  produce  a  bright,  clean  surface,  scrape  on  to  the  penny  about 
a  grain  of  the  pill  to  be  tested,  add  to  it  three  grains  of  iodide  of 
potassium  and  three  drops  of  water,  and  mix  them  with  the  point 
of  a  penknife.  If  mercury  is  present,  a  silvery  stain  will  be 
found  on  the  copper.  Where  the  metal  exists  as  blue  pill,  the 
reaction  requires  more  time,  but  it  is  equally  certain.  The 
experiment  can  easily  be  tried  with  a  compound  cathartic,  or  a 
Plummer's  pill. 
