CLEANING  AND  PRESERVATION  OF  ENGRAVINGS.  399 
which  resists  the  penetration  of  the  water,  and  motion  is  neces- 
sary to  remove  this  as  well  as  to  allow  the  colored  solutions 
formed  to  pass  away.  This  motion  may  be  given  by  holding 
the  supporting  sticks  and  passing  the  mass  from  end  to  end 
of  the  bath,  or  slowly  up  and  quickly  down,  enabling  the  sheets 
to  become  separated  momentarily.  Discolored  water  may  be 
drawn  off,  the  apron  and  contents  resting  on  the  bottom  and 
sides,  and  fresh  water  be  slowly  admitted  to  replace  it.  Cold 
water  can  be  substituted  for  warm,  longer  time  being  allowed 
for  its  action.  When  the  prints  no  longer  add  color  to  the 
water  after  being  agitated,  the  water  must  be  withdrawn  and 
replaced  by  such  a  portion  as  will  barely  cover  the  paper. 
Half  a  pound  of  bleaching  powder  (chloride  of  lime)  mixed  to  a 
paste  first  in  cold  water,  and  then  added  to  two  quarts  of  cold 
water  and  well  stirred  from  time  to  time  for  six  hours,  will  afford 
a  nearly  clear  fluid  resting  on  a  white  deposit  in  the  earthenware 
vessel.  A  portion  of  the  clear  part  of  this  fluid  must  be  added 
to  the  water  in  the  bath,  until  both  taste  and  odor  denote  the 
presence  of  chlorine  in  the  water.  Motion  being  given  to  the 
paper,  the  bleaching  effect  of  chlorine  will  be  perceived,  or  its 
odor  in  the  water  will  have  been  lost,  when  more  must  be  added 
so  that  the  odor  or  taste  of  chlorine  must  be  present  in  the  water 
two  or  three  hours. 
The  action  of  the  chlorine  on  the  parts  previously  wet  with 
the  aeid  will  remove  nearly  every  kind  of  discoloration,  while 
the  brown  hue  of  the  paper  giving  place  to  perfect  whiteness, 
the  light  and  shadows  of  the  engraving  become  of  their  original 
perfectness,  and  the  picture  will  be  as  distinct  as  when  it  was 
first  impressed.  It  has  happened  in  a  few  trials,  when  the  prints 
were  long  stained,  and  they  did  not  yield  to  the  weak  chlorine 
water,  that  resort  was  to  have  a  little  mineral  acid  to  develope  free 
chlorine  in  the  bath.  One  ounce  of  muriatic  acid  was  added  to 
one  pint  of  cold  water,  and  the  weak  acid  thus  formed,  mixed  in 
the  water  of  the  bath,  soon  caused  the  bleaching  of  every  fibre 
in  the  paper. 
After  the  bleaching  the  water  must  be  drawn  off,  the  paper 
drained,  fresh  clear  water  admitted,  and  the  paper  moved  through 
the  water  to  thoroughly  wash  away  all  adhering  chlorine.  Seve- 
ral quantities  of  water  may  be  used,  the  paper  being  each  time 
drained ;  and  finally,  the  whole  mass,  raised  by  the  handles, 
