ON  THE  PREPARATION  OE  DRYING  OIL 
169 
when  both  the  solutions  of  sulphate  of  manganese  and  borax 
were  diluted  as  much  as  possible  and  mixed  boiling.  The  sicca- 
tive action  upon  the  oil  must  therefore  be  ascribed  to  the  oxide, 
and  not  to  the  protoxide. 
By  further  experiments  the  author  found  that  the  boracic  acid 
is  quite  superfluous,  and  that  free  oxide  of  manganese  or  its 
hydrate  is  as  efficacious  as  the  borate.  The  oil  need  only  be 
heated  for  a  very  short  time  (about  a  quarter  of  an  hour)  with 
about  one-eighth  per  cent,  of  oxide  or  hydrated  oxide  of  manganese. 
The  heat  applied,  need  not  approach  the  boiling-point  by  a  long 
way  ;  but  no  general  temperature  can  be  given,  as  new  oil  has  a 
much  higher  boiling-point  than  old.  The  siccative  quality,  how- 
ever, increases  with  the  heat.  But  as  the  oil  becomes  darker  and 
thicker  in  proportion  to  the  heat  to  which  it  is  exposed,  it  is  the 
best  plan  in  general  to  remove  it  from  the  fire  as  soon  as  it  clears 
and  begins  to  fume  very  slightly.  Streaks  of  it  now  become 
firm  in  twenty-four  hours.  To  obtain  the  drying  oil  of  a  very 
pale  color,  it  must  be  heated  still  less.  The  drying  is  thus 
retarded  several  hours,  but  the  color  has  scarcely  become  per- 
ceptibly brownish,  whilst  in  the  former  case  it  always  acquires 
a  chestnut-brown  color. 
The  author  obtained  a  wine-yellow  oil,  quite  unaltered,  without 
heat,  by  mixing  1  per  cent,  of  hydrated  lime  with  a  linseed-oil 
four  years  old,  which  dried  by  itself  in  three  days.  After  being 
frequently  stirred  for  two  days,  a  streak  of  it  was  perfectly  firm 
in  twenty-four  hours.  Oil  of  the  same  year,  however,  did  not 
become  siccative  even  by  boiling  with  lime. 
The  oil  dissolves  very  little  of  the  small  quantity  of  oxide  of 
manganese,  and  the  salt,  when  removed,  may  be  repeatedly  used 
in  the  preparation  of  drying  oil.  When  prepared  oil  is  mixed 
with  an  equal  weight  of  crude  oil,  it  requires  nearly  twice  as 
long  to  dry  ;  with  twice  the  quantity,  twenty  hours  longer ;  and 
with  three  times  the  quantity,  another  twelve  hours ;  but  the 
time  necessary  for  the  solidification  of  the  coating,  gradually 
diminishes  a  little  by  long  standing. — Ohem.  Graz.,  Nov.  15, 
1856,  from  Kunst-und  Cfewerbeblatt,  fitr  Bay  em. 
