422  Bleaching  Agents  and  Writing  Inks,  {^^au-^i^*"™' 
Xickel  salts  behave  similarly,  but  the  addition  of  sodium  tartrate 
prevents  the  reprecipitation  with  acetic  acid. 
Ferrous  salts  yield  a  precipitate  soluble  in  excess,  but  completely 
reprecipitated  on  addition  of  acetic  acid. 
Ferric  salts  give  a  precipitate  soluble  in  excess  and  not  precipitated 
by  acetic  acid;  on  addition  of  acetic  acid  and  sodium  sulphite,  repre- 
cipitation is  complete. 
Aluminium  salts  give  a  precipitate  soluble  in  excess,  but  completely 
reprecipitated  by  adding  acetic  acid  and  boiling ;  the  addition  of  sodium 
tartrate  prevents  reprecipitation. 
Uranic  salts  give  a  precipitate  soluble  in  excess  and  not  reprecipitated 
by  acetic  acid. 
Chromic  salts  give  a  bright  green  precipitate  which  is  scarcely  solu- 
ble in  excess  even  on  boiling.  Acetic  acid  prevents  the  precipitation 
of  chromic  salts,  but  the  solution  becomes  turbid ;  the  addition  of 
sodium  tartrate  prevents  the  turbidity. 
From  the  above  results  it  will  be  seen  that  by  means  of  sodium 
pyrophosphate  copper  can  be  separated  from  cadmium,  cobalt  from 
nickel,  manganese  and  zinc  from  ferric  salts,  manganese  from  aluminium 
and  uranium,  and  ferrous  salts  from  aluminium  and  uranium,  possibly 
also  from  chromium  and  ferric  salts.  Cadmium,  zinc,  manganese, 
cobalt,  nickel,  possibly  also  ii'on  and  aluminium,  can  be  estimated  as 
pyrophosphates. 
ACTION  OF  BLEACHIXG  AGEXTS  ON  WRITING  INK.^ 
By  E.  Ietine. 
The  author  made  a  series  of  experiments  to  ascertain  whether  it  is 
possible  to  tell  the  age  of  writing,  and  if  writing  has  been  executed  at 
one  and  the  same  time,  and  if  so,  at  what  time.  He  selected  writing 
one  day,  six  months,  12  months,  2  years,  6  years,  14  years,  and  22 
years  old,  and  exposed  these  writings  to  the  action  of  a  very  dilute 
solution  of  bleaching  powder,  sp.  gr.  1*001.  In  six  minutes,  the  new- 
ly-written matter  had  disappeared  ;  in  from  nine  to  twelve  minutes,  the 
writing  of  six  months  ago  had  disappeared ;  in  twenty  minutes,  the 
writing  of  two  years  had  partly  disappeared,  whilst  in  a  like  time  the 
writing  of  six  years  ago  was  not  greatly  affected,  of  14  years  ago  very 
^Jour.  Chem.  Soc.,  1888,  764;  /.  Soc.  Chem.,  lad.,  VI,  807—808. 
