CHEMISTRY  OF  OIL  PAINTS. 
259 
ture  of  paint,  and  the  chemical  changes  involved  in  the  drying 
of  oils.  As  regards  linseed  oil,  we  are  told  that  the  essential 
constituent  is  "linolein,"  a  compound  of  glycerin  and  linoleic 
acid.  The  latter  body  the  author  could  not  obtain  quite  pure, 
but  he  decides  that  its  formula  is  HO,C32H2703.*  When  ex- 
posed to  air,  linoleic  acid  rapidly  oxidises,  first  to  "  linoxic  acid," 
a  sticky  body  resembling  turpentine.  On  longer  exposure, 
"  lynoxyn  "  is  produced.  This  is  a  tough,  leathery  substance, 
sharing,  we  may  say,  many  of  the  properties  of  caoutchouc.  It 
is  soluble  in  the  same  menstrua,  and  can  be  vulcanised  like 
india-rubber.  It  is  manufactured  in  considerable  quantities  in 
this  country  (United  States),  and  is  the  binding  material  used  to 
consolidate  emery  wheels.  It  forms  also  the  surface  of  linoleum 
cloth.  According  to  Mulder,  there  are  two  linoxyns,  the  white 
and  red  ;  the  white  modification  becomes  red  on  exposure  to 
80°  Centigrade,  and  the  red  again  turns  white  on  exposure  to 
sunlight.  The  browning  of  white  paint  in  dark  places  the  author 
ascribes  to  the  gradual  change  of  white  linoxyn  into  red.  Oxi- 
dation does  not  end  with  the  production  of  linoxyn.  It  still 
proceeds  to  the  complete  decay  of  the  material,  as  is  seen  in 
very  old  paint. 
One  useful  result  of  Mulder's  labor  is  a  simple  process  for  pre- 
paring a  good  colorless  drying  oil.  For  this  purpose  it  is  only 
necessary  to  boil  linseed  oil  for  two  hours  with  three  per  cent,  of 
red  lead,  filter  it,  and  then  expose  it  to  sunlight  in  large  shallow 
vessels,  frequently  renewing  the  air  above.  Another  result  is  a 
denial  of  the  existence  of  albuminous  and  gummy  matter  in 
linseed  oil,  to  which  are  ascribed  the  slowness  of  drying  of  un- 
boiled oils.  For  these  matters  Mulder  searched  in  vain,  and  at 
last  came  to  the  conclusion  that  they  had  no  existence.  Oxides 
and  acetates  of  lead,  he  tells  us,  act  as  driers,  not  by  precipita- 
ting albuminous  matters,  but  by  forming  a  little  linoleate  of  lead, 
which  rapidly  oxidises  and  communicates  its  activity  to  the  oil. — 
Chemist  and  Druggist,  March,  1868,  from  Journ.  Chem.  Soc. 
vol.  xviii,  p.  117. 
*This  agrees  with  the  formula  given  in  Watt's  Dictionary,C  j  6^2  802, 
in  which  the  modern  atomic  weights  of  carbon  and  oxygen  are  adopted. 
