RECOVERY  OF  GOLD  AND  SILVER  IN  ELECTRO-PLATING. 
519 
salt  or  the  halogen  combined  with  the  ammonium  unites  with  the 
metal  which  has  been  combined  with  the  cyanogen.  In  the  pre- 
sent case  muriate  of  ammonia  forms  chloride  of  potassium,  chlo- 
ride of  iron  (when  ferrocyanide  of  potassium  has  been  employed) 
and  chloride  of  gold.  The  latter  is  readily  decomposed,  with  for- 
mation of  metallic  gold ;  the  other,  at  least  partially,  with  sepa- 
ration of  peroxide  of  iron,  in  fine  crystalline  scales.  Undecom- 
posed  chloride  of  iron,  as  well  as  chloride  of  potassium,  may  be 
extracted  with  water  after  complete  decomposition,  for  which  a 
slight  red  heat  is  sufficient ;  the  gold  forms  a  coherent  spongy 
mass ;  the  iron,  fine  light  scales,  which  are  readily  separable  by 
mechanical  means.  If  any  gold  remain  in  the  form  of  dust  with 
the  peroxide  of  iron,  it  may  be  dissolved  out  with  nitromuriatic 
acid  (the  calcined  oxide  of  iron  long  resisting  the  action  of  the 
acid,)  and  the  gold  thrown  down  by  protosulphate  of  iron.  In 
most  cases  this  mode  of  separation  will  be  unnecessary.  The  au- 
thor has  convinced  himself,  by  the  employment  of  measured  vol- 
umes of  the  same  solution  of  gold,  evaporation,  heating  with  mu- 
riate of  ammonia,  and  so  forth,  that  even  the  quantity  of  gold  in 
such  solutions  may  be  determined  with  sufficient  exactness. 
The  same  process  may  be  adopted  with  plating  fluids  ;  chloride 
of  silver  is  obtained  together  with  oxide  of  iron  (from  the  ferro- 
cyanide of  potassium ;)  the  chloride  is  readily  dissolved  by  am- 
monia ;  metallic  silver,  of  which  however  but  little  or  none  is 
formed,  is  extracted  by  nitric  acid.  It  is  unnecessary  to  say 
that  the  residue  is  operated  upon  in  the  usual  manner  to  obtain 
the  silver ;  nevertheless,  as  the  decomposition  of  the  plating 
fluids  may  be  effected  in  the  humid  way  by  means  of  sulphuret- 
ted hydrogen,  this  process  may  not  be  so  frequently  adopted  for 
silver. 
Lastly,  it  may  be  useful  to  inform  those  persons  who  occupy 
themselves  with  electro-plastic  processes,  that  the  employment  of 
chloride  of  ammonium  or  a  salt  of  ammonia  in  this  manner,  fur- 
nishes a  ready  means  of  testing  the  composition  of  such  fluids  as 
are  used  in  the  formation  of  a  galvanic  coating.  For  solutions 
of  copper  the  author  employs  sulphate  of  ammonia,  because  when 
muriate  of  ammonia  is  employed,  chloride  of  copper  is  formed, 
which  is  partially  volatilized  with  the  undecomposed  sal  ammo- 
niac, producing  a  loss  of  copper. — Chemical  Gazette,  Sept.  1853, 
from  Polytechn.  Oentralblatt,  1853,  p.  551. 
