540 
OZONE  AS  A  MEANS  OF  RESTORINa  ENGRAVINGS. 
ameter,  the  surface  of  which  has  been  scraped  bright,  in  a  wide 
necked  glass  carboy,  or  other  large  hollow  vessel,  pouring  in  as 
much  water,  at  about  30^  (C),  as  will  half  cover  the  phospho. 
rus,  closing  the  vessel  with  a  cork,  and  allowing  the  whole  to 
stand  until  the  jar  is  charged  as  strongly  as  possible  with  ozone, 
which  ordinarily  occurs  after  12  or  18  hours.  Then  without 
removing  the  phosphorus  or  water,  the  paper  to  be  bleached, 
which  has  been  moistened  with  water,  rolled  up,  and  fastened  to 
a  platinum  wire  in  a  suitable  manner,  is  hung  in  the  middle  of 
the  vessel.  The  cork  is  now  restored  and  the  apparatus  left  to 
itself.  The  roll  of  paper  is  soon  surrounded  with  the  fumes 
arising  from  the  phosphorus,  and  the  stains  gradually  disappear. 
The  rapidity  of  the  operation  of  course  depends  upon  the  nature 
of  the  substance  to  be  discharged — three  days  having  been  the 
longest  time  required  in  any  of  the  experiments.  Prints  which 
had  merely  become  brown  by  age  and  those  stained  with  cofiPee 
usually  became  perfectly  white  and  clean  in  the  course  of  48  hours. 
The  action  of  the  ozone,  however,  must  not  be  continued  too  long 
lest  some  of  the  finer  lines  of  the  engraving  should  be  injured. 
After  all  the  spots  have  disappeared,  the  paper  is  strongly  acid, 
and  if  allowed  to  dry  when  in  this  condition  would  become  ex- 
ceedingly brittle  and  also  dark  colored.  It  is  consequently 
necessary,  to  remove  the  acid  completely.  In  order  to  accom- 
plish this  the  paper  is  placed  in  water  which  is  frequently 
renewed  and  allowed  to  lie  there  until  a  bit  of  blue  litmus  paper 
pressed  against  it  is  no  longer  reddened.  The  paper  is  then 
passed  through  water  to  which  a  few  drops  of  a  solution  of  soda 
have  been  added  and  is  spread  upon  a  glass  plate,  this  is  slightly 
inclined,  and  a  fine  stream  of  water  is  allowed  to  flow  over  the 
paper  during  24  hours.  After  the  paper,  on  exposure  to  the 
air,  has  become  dry  enough  to  remove  from  the  glass  without 
danger  of  tearing,  it  is  taken  off  and  pressed  dry  between  folds 
of  filter  paper. 
The  author  remarks  that  in  case  the  process  were  attempted 
on  a  larger  scale  it  would  probably  be  well  to  have  glass  troughs 
or  boxes  blown  of  the  desired  form,  since  it  is  not  easy  to  pre- 
pare suitable  vessels  by  any  process  of  fastening  together  pieces 
of  glass,  the  cement  being  attacked  by  ozone. 
