VARIETIES. 
469 
and  when  nearly  dry  immersed  in  nitrate  of  silver  or  otherwise,  so  as  to 
prepare  them  for  receiving  the  deposit  of  copper.  This  done,  they  are 
plunged  into  cold  water,  and  carefully  dried  in  a  suitable  kiln,  after  which 
they  are  placed  in  sawdust  for  twenty  four  hours  to  prevent  oxidation. 
The  next  operation  is  to  remove  any  roughness  on  the  surface  which  the 
articles  may  have  contracted.  This  is  done  by  means  of  sand  paper  or 
silver  s^nd,  and  brushing  with  a  scratch-brush  till  they  are  made  perfectly 
smooth,  care  being  taken  to  remove  any  greasy  matter  from  the  surface. 
The  copper  and  silver  have  now  to  form  one  alloy,  so  as  to  unite  them 
firmly  together.  For  this,  a  film  of  quicksilver  is  employed,  dissolved  in 
nitric  acid.  This  is  set  aside  to  crystallize,  and  the  crystals  are  dissolved 
to  form  the  desired  solution  ;  the  articles  are  then  dipped  therein,  passed 
through  water,  and  introduced  into  the  vat  containing  the  silver  solution. 
The  silver  solution  consists  of  metallic  silver  dissolved  in  nitric  acid 
diluted  with  water,  with  the  addition  of  certain  cyanides,  till  a  given  result 
is  obtained.  This  is  followed  by  a  repetition  of  the  copper  process  only 
with  the  solution,  and  the  articles  in  due  time  appear  in  their  silver  garb, 
ready  to  receive  the  chasing. 
Gold  is  prepared  by  being  dissolved  in  nitro-muriatic  acid.  This  chloride 
is  digested  with  calcined  magnesia,  and  the  whole  precipitated  into  an 
oxide.  The  oxide,  boiled  in  strong  nitric  acid,  dissolves  the  magnesia,  and 
when  washed  forms  a  cyanide  of  gold  and  potassium. 
The  films  of  gold  are  deposited  in  the  vessels  by  means  of  voltaic  electri- 
city, a  process  requiring  careful  observation,  both  to  insure  an  adequate 
coating  and  the  proper  color;  if  defective,  it  will  have  to  be  repeated. 
The  time  of  exposure  to  the  heat  depends  upon  its  intensity,  and  the  color 
desired  to  be  produced  ;  these  must  be  the  fruits  of  experience,  and  will 
not  fail  to  be  acquired  by  practice. 
The  finishing  process  is  the  burnishing,  which  is  the  same  as  with  the 
silver,  and  requires  no  further  illustration. — F.  List.  Jour.,  from  Journal  of 
the  Society  of  Arts. 
Metallic  Cement. — According  to  Serbat,  a  metallic  cement,  which  answers 
for  all  purposes  and  becomes  hard  in  the  heat,  may  be  obtained  in  the  fol- 
lowing way : — 100  parts  of  oxide  of  zinc,  with  the  same  quantity  of  sul- 
phate of  lead,  are  triturated  with  30  parts  of  linseed  oil,  and  then  a  mixture 
consisting  of  100  parts  of  black  oxide  of  manganese  and  100  parts  of  per- 
oxide of  iron  added  until  the  mass  forms  a  stiff  dough.  This  is  beaten  in 
a  mortar  for  twelve  hours,  during  which  the  remainder  of  the  above  mix- 
ture of  iron  and  manganese  is  added  by  degrees.  The  goodness  of  the 
cement  may  be  recognized  by  its  not  crumbling  when  rolled  out  between 
the  fingers. — Annals  of  Pharmacy,  July,  1853,  from  Le  Genie  Industriel. 
Electro-Tele  graphic  Development. — The  extent  of  telegraphic  communication 
completed  and  in  operation  throughout  the  world  at  the  beginning  of  the 
present  year  may  be  estimated,  as  far  as  can  be  gathered  from  the  returns,  at 
