PreparciHon  of  the  MelaU  to  be  Nick'
elled.  The  treatment  of  iron  and  steel
requires  no  further  explanation.  We
advise  to  first  immerse  the  articles  for
some  time  in  a  boiling  hot  solution  of
caustic  soda  or  potash,  next  to  rub  them
thoroughly  witn  a  brush,  then  to  rinse
with  cold  water,  and  finally  to  dip
them  into  an  acid  pickle  consisting  of
1  part  of  sulphuric  acid  and  2  of  hydro-
chloric acid  to  10  of  water,  after  which
thev  are  again  rin8ed,thoroughly  rubbed
witn  fine,  washed  pumice-stone  or  Vi-
enna lime,  rinsed  off,  and  at  once  brought
into  the  oath.  Fine  polished  instru-
ments of  iron  and  steel  for  surgical,
dental,  and  other  purposes,  scissors,
knives,  and  telegraphic  instruments  are
treatea  in  the  same  manner,  but  in
place  of  the  washed  pumice-stone  they
should  be  brushed  with  whiting  or  trip-
oil,  or,  what  is  still  better,  with  infu-
sorial earth.  Brass,  bronze,  Britannia
metal,  etc.,  are  also  treated  with  a  hot
solution  of  caustic  soda  or  potash,  then
rubbed  and  brushed^  rinsed  with  water,
and  at  once  placed  in  a  solution  of  cy-
anide of  potassium.  They  are  then
cleansed  with  a  bristle  brush  kept  for
that  purpose,  carefully  rinsed  in  water,
and  at  once  brought  into  the  bath .  The
variegated  colors  produced  upon  brass
by  the  action  of  the  solution  of  caustic
soda  disappear  almost  instantaneously
in  the  solution  of  cyanide,  and  a  bright
surface  of  the  metal  is  sure  to  be  ob-
tained. Special  attention  must  be  paid
to  the  careful  rinsing  of  the  articles,
especially  if  they  have  hollow  places
and  depressions,  after  thev  have  been
treated  in  the  solution  of  cyanide  of

Eotassium,  to  prevent  the  nickelling
ath  from  being  contaminated  by  the
cyanide.  For  many  articles  of  brass
having  more  or  less  matt  and  polished
places,  it  is  Sufficient  to  dip  them  (after


having  been  freed  from  all  fiitfy  sub-
stances by  boUing  potash  and  sabse-
quently  rinsing  in  water)  into  the  mixt-
ure of  acids,  then  to  rinse  them  again,  and
to  bring  tnem  at  once  into  we  bath.
