290 
Modern  Pai-nt  Vehicles. 
Am.  Tour.  Pharm. 
May,  1919. 
resolves  itself  into  "What  is  good  oil?"  and  finally  "What  is  a 
paint  oil,  and  when  is  an  oil  a  paint  oil  ?  " 
In  general,  when  we  speak  of  a  paint  •"  vehicle,"  we  mean  all 
the  liquid  portion  of  the  paint. 
This  vehicle  can,  in  all  cases,  be  split  into  two  fairly  distinct  parts : 
the  "  volatile  oils  or  thinners  "  and  the  "  non-volatile  or  fixed  oils," 
which  form  the  bulk  of  the  vehicle. 
Among  the  "  volatiles  "  (which  can  be  distilled  off  from  the  rest 
of  the  paint  in  a  current  of  steam  and  examined  separately)  we  in- 
clude turpentine  (both  wood  turpentine  and  gum  spirits),  the  various 
turpentine  substitutes  and  benzine  or  naphtha. 
The  only  comparatively  new  materials  here  are  the  turpentine 
substitutes,  which  possess  many  valuable  properties,  and  which  for 
the  last  ten  or  fifteen  years  have  been  distilled  from  petroleums  either 
of  asphaltic  or  paraffine  bases.  They  are  bought  and  sold  under 
very  rigid  requirements  and  specifications  as  regards  flash  point, 
distillation,  specific  gravity,  etc. 
By  far  the  largest  part  of  the  vehicle  consists  of  the  non-volatile 
or  fixed  oil  portion.  This  usually  consists  of  pure  linseed  oil,  except 
in  the  flat  wall  paints  and  the  enamels,  which  in  one  case  may  con- 
tain China  wood  oil,  and  in  the  other  contain  varnishes. 
The  non-volatile  or  fixed  oils  fall  naturally  into  two  great  classes : 
(1)  vegetable  and  (2)  animal  oils  and  fats.  These  two  groups  are 
both  further  sub-divided  by  chemists  into  four  sub-groups :  ( 1 )  solid 
fats;  (2)  non-drying  oils ;  (3)  semi-drying  oils;  (4)  drying  oils. 
The  solid  fats  are  not  of  interest  to  us.  The  non-drying  oils 
(even  when  vegetable  or  animal,  and  not  mineral),  are  not  of 
interest  either  to  the  conscientious  manufacturer  or  master  painter. 
The  last  class  (the  drying  oils)  and  sometimes  a  mixture  of  one 
or  more  of  ithem  with  a  properly  balanced  percentage  of  one  of  the 
third  class  of  semi-drying  oils,  is  the  only  group  which  is  really 
wiprth  our  attention.  Drying  oils  suitable  for  use  in  paint  may  be 
either  vegetable  (linseed,  soya,  perilla)  or  animal  (fish  or  men- 
haden) oils.  Experiments  and  tests  have  even  been  made  on  whale 
oil  and  porpoise  jaw  oil,  to  indicate  the  breadth  and  scope  of  the 
field  of  investigation,  but  they  were  not  very  satisfactory.' 
The  next  questions  which  naturally  come  to  mind  at  this  point 
are:  "How  does  a  drying  oil  dry?"  and  "Why  does  it  dry  to  an 
elastic  film,  while  some  other  oils  do  not;  and  some  (the  heavy 
mineral  oils)  never  dry?" 
