DULOS'  PROCESSES  OF  ENGRAVING. 
325 
cumstanccs  arsenic  is  easily  attacked,  giving  arsenious  acid  and 
a  little  arsenic  acid  ;  antimony,  on  the  contrary,  is  attacked 
with  more  difficulty.  However  that  may  be,  if  ammonia  is 
looked  for  in  the  liquids  obtained  it  will  be  found  that  these  two 
bodies  have  behaved  like  phosphorus,  with  this  difference,  that 
phosphorus  gives  more  ammonia  than  does  arsenic,  and  arsenic 
more  than  antimony. 
Whe  phenomenon  of  the  formation  of  ammonia  by  the  decom- 
position of  water  under  the  influence  of  nitric  acid  has  hitherto 
been  observed  only  with  metals  of  the  third  and  fourth  section, 
as  iron,  zinc,  tin,  &c. 
The  above  observations  show  that  this  phenomenon  is  not 
limited  to  these  metals,  but  belongs  equally  to  the  metalloids  of 
the  phosphorus  group. — Lond.  Oheni.  News,  May  21, 1864,  from 
Bulletin  de  la  Societe  Ghimique,  vi.  163. 
DULOS'  PROCESSES  OF  ENGRAVING. 
A  copper  plate,  on  which  the  design  has  been  traced  with 
lithographic  ink,  receives,  by  the  action  of  the  pile,  a  deposit 
of  iron  on  the  parts  untouched  by  the  ink  ;  the  ink  having  been 
removed  by  means  of  benzine,  the  white  portions  of  the  design 
are  represented  by  the  layer  of  iron,  and  the  black  by  the  cop-, 
per  itself ;  the  plate  is  then  plunged  into  a  bath  of  cyanide  of 
silver,  under  a  galvanic  current,  and  the  silver  is  deposited  on 
the  copper  only.  In  this  condition  mercury  is  poured  over  the 
plate,  which  attaches  itself  to  the  silvered  portions  only,  appear- 
ing in  relief,  and  taking  the  place  of  the  lithographic  ink.  Then 
take,  in  plaster  or  melted  wax,  an  imprint,  the  cast  of  which 
presenting  the  counterpart  of  the  projections  of  mercury,  gives 
a  kind  of  copper  plate  engraving.  This  cast  has  not  sufficient 
strength  to  bear  the  press  ;  but  by  metallising  the  mould,  and 
depositing  upon  it,  electro  chemically,  a  layer  of  copper,  we 
obtain  an  exact  reproduction  of  the  original  projections  of  mer- 
cury, and  in  some  sort  a  matrix  by  means  of  which  impressions 
of  the  plate  may  be  produced  ad  infinitum. 
For  typographic  engraving  (figures  in  relief),  the  plate  of 
copper  should  receive,  on  leaving  the  hands  of  the  designer,  a 
layer  of  silver,  deposited  only  on  the  part?  untouched  by  the 
