24        CHEMICAL  AND  PHARMACEUTICAL  MANIPULATIONS. 
can  be  made  also  with  sealing-wax,  which  takes  the  minutest  lines  of  the 
original.  Reverses  may  be  procured  in  lead  by  forcing  the  matrix  into  a 
bright  surface  of  it,  either  by  pressure  or  blows. 
Non-conducting  Substances. —As  gutta  percha,  wax,  plaster  of  Paris,  and 
many  of  the  materials  used  for  making  moulds  are  non-conductors,  it  is 
necessary  to  coat  the  surface  on  which  it  is  desired  to  deposit  metal  with 
some  conducting  substances.  The  best  and  easiest  of  application  is  plum- 
bago or  black  lead.  A  copper  band  or  wire  is  fastened  around  the  edge  of 
the  mould,  and  the  ends  formed  into  a  hook,  or  punched  with  holes,  to 
make  the  connection  with  the  battery.  A  fine  brush  is  dipped  into  the 
plumbago  and  passed  thoroughly  over  the  face  of  the  mould,  all  excess  of 
black  lead  being  carefully  removed,  and  the  brushing  continued  until  every 
part  is  covered  and  brightly  polished.  This  treatment  will  insure  a  quick 
and  even  deposit.  In  wax  moulds  it  is  only  necessary  to  insert,  in  the  edge 
of  the  mould,  a  piece  of  copper  by  which  to  attach  it  to  the  battery-pole.  In 
every  case,  however,  the  conducting  coating  must  extend  to  and  be  in  con- 
tact with  the  battery  connection.  In  using  metal  moulds,  those  parts  on 
which  metal  is  not  to  be  deposited  should  be  covered  with  wax  or  some  kind 
of  varnish. 
The  battery  connection  is  most  conveniently  and  perfectly  formed  by 
soldering  a  copper  wire,  flattened,  at  one  end  to  the  metal  mould. 
Bronze  powder  is  sometimes  used  instead  of  plumbago  and  in  the  same 
manner.  Flowers,  and  other  objects  to  which  plumbago  is  not  applicable, 
may  be  rendered  conducting  by  a  film  of  gold  or  silver.  This  is  applied 
through  the  medium  of  a  solution  of  phosphorus  in  bi-sulphuret  of  carbon. 
The  solution  is  made  by  dissolving  1  ounce  of  phosphorous  in  15  ounces  of 
bi-sulphuret  of  carbon,  and  adding  thereto  1  ounce  of  wax,  1  ounce  of  as- 
phalte,  1  ounce  of  spirits  of  turpentine,  and  1  drachm  of  india-rubber.  The 
india-rubber  must  be  dissolved  in  turpentine,  and  the  asphalte  in  the  phos- 
phorous solution.  The  wax  is  melted  first,  the  turpentine  and  india-rubber 
stirred  in,  and  then  the  asphalte  and  phosphorous  solution  added. 
This  should  be  done  with  caution  over  a  water-bath,  as  the  components 
are  highly  inflammable.  The  bi  sulphuret  of  carbon  being  very  volatile,  the 
eolation  should  be  kept  in  a  well-stoppered  bottle.  "  The  solution,  as  above 
prepared,  is  applied  to  the  surfaces  of  non-metallic  substances  by  immer- 
sion or  brushing  ;  the  article  is  then  dipped  in  a  dilute  solution  of  nitrate 
of  silver  or  chloride  of  gold  ;  in  a  few  minutes  the  surface  is  covered  with  a 
fine  film  of  metal,  sufficient  to  insure  a  deposit  of  any  required  thickness  on 
the  article's  being  connected  with  a  battery.  The  solution  intended  to  be 
used  is  prepared  by  dissolving  1  ounce  of  silver  in  nitric  acid,  and  after- 
wards diluting  with  3  gallons  of  water ;  the  gold  solution  is  made  by  dis- 
solving 2  pennyweights  of  gold  in  aqua  regia,  and  then  diluting  with  a  gallon 
of  water." 
Gold  Solution. — Convert  a  half  ounce  of  gold  into  terchloride,  dissolve  the 
