66 
Nascent  Silver  Iodide. 
[  Am.  Jour.  Pharm. 
I    February.  1906. 
ent  elements,  which  are  known  to  be  active  and  highly  efficient 
antiseptics. 
Bearing  in  mind,  then,  these  several  well-known  facts  relating  to 
silver  iodide,  the  rationale  of  the  use  of  this  salt  for  local  applica- 
tion as  an  antiseptic  is  quite  evident.  Being  itself  insoluble,  it  is 
not  caustic  or  irritating,  while  the  fact  that  it  is  readily  decomposed 
in  the  presence  of  reducing  agents  into  active  antiseptic  materials, 
would  readily  suggest  its  use  for  this  purpose  as  being  practically 
ideal. 
That  the  activity  of  the  silver  iodide  varies  with  age,  the  exposure 
to  which  it  has  been  subjected,  and  also,  in  a  measure  at  least,  to 
the  relative  fineness  of  the  precipitate,  are  facts  also  well  known  to 
photographers,  and  may  readily  be  demonstrated  by  using  as  a  test 
reagent  either  a  solution  of  one  of  the  well-known  reducing  agents 
used  for  developing  photographic  negatives,  or  a  specimen  of  alka- 
line urine. 
With  a  finely  divided  precipitate  that  has  not  been  unduly  ex- 
posed, the  reduction  takes  place  very  rapidly,  while  an  old,  or  a 
comparatively  coarse,  silver  iodide  may  require  several  minutes 
before  distinct  evidences  of  decomposition  manifest  themselves. 
This  reduction  test,  it  may  be  added,  should  and  does  offer  a  read- 
ily available  method  for  determining  the  activity,  and  therefore  the 
desirability  of  any  given  sample  of  silver  iodide. 
The  most  available  form  for  using  nascent  silver  iodide  is  that  of 
a  mixture  or  an  emulsion,  being  practically  a  simple  suspension  of 
the  freshly  precipitated  silver  iodide  in  a  viscid  liquid.  This  vehi- 
cle, or  suspending  medium,  may  be  varied  to  suit  individual  need  or 
preference,  any  one  of  the  bland,  inactive,  mucilaginous  substances, 
such  as  Irish  moss,  quince  seed,  salep  or  tragacanth,  being  readily 
available. 
A  mixture  containing  approximately  3  per  cent,  of  silver  iodide 
has  been  found  to  be  generally  most  satisfactory.  In  preparing 
such  a  mixture  it  should  always  be  borne  in  mind  that  the  result- 
ing silver  iodide  is  nearly  40  per  cent,  heavier  than  silver  nitrate, 
and  that  therefore  a  corresponding  smaller  quantity  of  the  latter  salt 
should  be  used. 
To  be  most  efficient  the  mixture  should  be  freshly  prepared,  and 
should  be  kept  in  a  cool,  dark  place.  As  noted  before,  the  degree 
of  fineness  of  the  resulting  precipitate  also  plays  a  very  important 
