n6  Hydrargyrum  Iodidum  Ruhrum,  etc,  {Km'^;^Xm' 
oxide  of  mercury  of  the  U.  S.  P.,  could  be  replaced  with  con- 
siderable advantage  by  some  mercurial  salt  or  preparation  pos- 
sessing the  advantages  of  ready  solubility,  and  concentration  in  small 
bulk  of  a  considerable  quantity  of  mercury.  For  this  purpose,  I  would 
suggest  the  mercuric  nitrate.  It  can  readily  be  prepared  by  dissolving 
mercury  in  a  slight  excess  of  nitric  acid,  and  then  can  be  used  either 
strong  or  diluted  with  water  to  any  degree  necessary.  For  general 
purposes,  the  officinal  liquor  hydrargyri  nitratis  answers  admirably. 
Two  troy  ounces  of  liq.  hydrarg.  nit.  (representing  384  grs.  mercury) 
were  diluted  with  an  equal  bulk  of  water,  and  then  660  grs.  of  iodide 
potassium  dissolved  in  fgiv  water  gradually  added,  until  no  farther  pre- 
cipitation took  place.  The  resulting  precipitate  of  red  iodide  of  mer- 
cury was  collected  on  a  filter,  washed  with  cold  water,  and  then  dried. 
It  weighed  868  grs.,  being  a  difference  of  only  a  few  grains  from  the 
estimated  theoretical  yield,  and  seemed  to  possess  all  the  qualities  of  a 
good  article.  The  manipulations  necessary  for  the  preparation  of  this 
salt  were  all  conducted  in  a  vessel  of  8  ozs.  capacity,  and  with  the 
expenditure  of  about  ten  minutes'  attention  ;  whereas,  if  the  officinal 
process  had  been  followed,  a  vessel  at  least  five  times  as  large  would 
have  been  required,  and  considerably  more  time  needed.  Another  ad- 
vantage can  be  also  found  in  the  fact  that  the  process  is  considerably 
cheaper  than  that  of  the  U.  S.  P.  In  practice,  I  have  found  it  neces- 
sary to  use  a  little  more  than  the  theoretical  quantity  of  iodide  potas- 
sium, in  order  to  allow  for  moisture  in  the  salt  as  well  as  to  thorough- 
ly insure  the  decomposition  of  the  mercuric  nitrate.  On  the  other 
hand,  care  must  be  taken  not  to  add  a  large  excess  of  iodide  potassium, 
on  account  of  the  solubility  of  the  mercuric  iodide.  For  preparing  the 
mercuric  iodide,  I  would  therefore  propose  the  following  formula  : 
R 
Mercury,         .  .              •              •               1000  grs. 
Nitric  acid,  .   •                          •              •         1700  grs. 
Iodide  potassium,  .              .              .    1662  grs.  or  q-  s. 
Distilled  water,  .              .              •              .               q.  s. 
(Instead  of  the  mercury  and  nitric  acid  gv  &  9ii  of  liq.  hydrarg.  nit. 
can  be  used.) 
Dissolve  the  mercury  in  the  nitric  acid  by  the  aid  of  a  little  heat  (in 
laro-e  quantities  this  is  not  necessary,  as  the  reaction  between  the  acid 
and  mercury  generates  sufficient  heat),  and  dilute  with  an  equal  bulk  of 
water.    Then  add  the  iodide  potassium,  dissolved  in  8  fluidounces  of 
