518  RECOVERY  OF  GOLD  AND  SILVER  IN  ELECTRO-PLATING. 
be  added,  into  a  deep  dark  red.  By  this  method  the  failure  of 
this  reaction  is  entirely  removed,  and  the  research  may  be  in 
such  way  quite  as  easily  and  certainly  conducted  as  the  well- 
known  reactions  on  strychnine  with  chromic  acid,  or  with  perox- 
ide of  lead  and  sulphuric  acid  Annals  of  Pharmacy,  Aug. 
1853,  from  Annalen  der  Qhemie. 
ON  THE  RECOVERY  OF  GOLD  AND  SILVER  FROM  THE  FLUIDS 
EMPLOYED  FOR  ELECTRO-PLATING  AND  GILDING. 
By  Prof.  Bolley. 
The  cyanide  of  gold  dissolved  in  an  excess  of  cyanide  of  potas- 
sium, resists  most  means  of  separation  ;  even  sulphuretted  hydro- 
gen produces  no  precipitate  in  it.  The  complete  separation  of 
the  gold  cannot  be  effected  in  the  humid  way  ;  and  this  has  given 
rise  to  the  propositions  of  Bottcher,  Hessenberg,  Eisner  and 
others,  to  evaporate  the  fluid,  mix  the  dry  residue  with  an  equal 
quantity  of  litharge,  fuse  the  mixture  at  a  strong  red  heat,  and 
dissolve  the  lead  from  the  fused  mass  by  hot  dilute  nitric  acid  ; 
by  this  means  the  gold  is  left  as  a  loose  sponge.  A  more  recent 
proposition  is  that  of  Wimmer,  by  which  the  mass  left  by  evapo- 
rating the  fluid  to  dryness  on  the  water-bath  is  mixed  with  one 
and  a  half  times  its  weight  of  nitrate  of  potash,  and  thrown  in 
small  portions  into  a  red-hot  Hessian  crucible.  The  explosions 
must  be  waited  for,  and  the  process  continued  until  the  entire 
mass  runs  smoothly.  The  first  process  has  nothing  against  it, 
except  the  necessity  of  a  strong  fire  and  the  employment  of  ni- 
tric acid  ;  the  second,  on  the  contrary,  is  very  unpleasant  and  un- 
safe in  its  performance.  It  is  sufficiently  well  known  that  there 
is  no  substance  with  which  nitrate  of  potash  detonates  so  violent- 
ly when  heated  as  with  cyanide  of  potassium.  If  the  portions 
of  the  mixture  employed  be  only  a  little  too  large,  very  violent 
explosions  are  produced,  which  cannot  take  place  without  loss. 
The  following  process  may  be  adopted  in  small  operations 
with  a  platinum  crucible  over  a  spirit-lamp.  The  dried  mass  of 
salts  is  mixed  with  an  equal  quantity  of  powdered  muriate  of 
ammonia,  and  gently  heated.  The  ammoniacal  salts  decompose 
the  cyanides  of  the  metals,  forming  cyanide  of  ammonium,  which 
is  decomposed  and  volatilized,  whilst  the  acid  of  the  ammoniacal 
