41 8  The  Commerce  in  Vegetable  Oils.  {An^S,S!"m* 
demand  for  oil  there,  as  an  article  of  diily  diet,  to  counteract  the 
binding  qualities  of  rice  and  other  cereal  foods  in  pastry-making, 
etc.,  has  led  to  the  manufacture  of  oil  from  all  sorts  of  sources. 
Vegetable  fixed  oils  are  usually  contained  in  the  seeds  of  plants, 
though  olive  oil  and  palm  oil  are  extracted  from  the  pulp  which 
surrounds  the  stone.  They  are  commonly  of  a  thickish  consistence 
and  unctuous  feel,  and  differ  from  volatile  oils  in  leaving  a  greasy 
stain  on  paper,  which  cannot  be  removed  by  heat  alone.  They  are 
sometimes  colorless,  occasionally  of  a  greenish  or  yellowish  hue ; 
when  pure,  semi-transparent,  with  little  smell  and  a  mild  taste. 
Fixed  oils  are  those  which  require  an  intense  heat  before  they 
give  out  vapor.  The  fixed  vegetable  oils  are  chiefly  expressed,  the 
seeds  or  raw  material  being  previously  ground  or  bruised,  and  the 
pulpy  matter  subjected  to  pressure  in  hempen  bags ;  a  gentle  heat 
being  generally  employed  at  the  same  time,  to  render  the  oil  more 
liquid.  Those  which  retain  their  transparency  after  they  have 
become  solid,  as  linseed,  nut,  poppy  and  hemp  seed,  are  called 
drying  oils,  while  others  which  assume  the  appearance  of  tallow  or 
wax  and  become  opaque,  as  olive,  almond,  rape  and  benne  are  called 
fat  oils. 
The  former  are  mostly  used  for  paints,  varnishes  and  printers' 
ink;  the  latter  are  consumed  as  food,  in  medicine,  soap-making 
and  other  branches ;  several  of  each  kind  being  likewise  exten- 
sively employed  in  the  arts  and  in  the  lubrication  of  machinery. 
The  division  of  oils  into  drying  and  non-drying  is  due  to  the  oleine 
which  alters  in  oxidizing.  The  product  of  this  alteration  is,  in  non- 
drying  oils,  an  acid  of  a  disagreeable  odor,  which  irritates  the 
throat ;  in  the  drying  oils  it  forms  an  actual  resin. 
India  and  Africa  are  the  chief  producing  countries  of  oil-yielding 
plants.  There  are  over  300  plants  known  in  India  to  yield  oils  or 
perfumes,  while  those  of  many  other  countries  also  furnish  fixed  or 
volatile  oils.  Some  are,  however,  not  articles  of  any  commercial 
importance. 
The  port  and  town  of  Marseilles,  from  its  facilities  for  obtaining 
supplies  from  Africa  and  India,  is  regarded  as  the  principal  Euro- 
pean centre  for  oil-crushing  and  the  utilization  of  oils. 
The  receipts  of  oil  seeds  and  their  manufacture  at  Marseilles,  in 
1887  and  1893,  were  as  follows,  in  metrical  quintals  of  2  cwt.: 
