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Modern  Paint  Vehicles. 
Am.  Tour.  Pharm. 
May,  1919. 
serves,  within  limitations,  as  a  measure  of  the  relative  serviceability 
of  oils  for  use  in  paints.  It  is  expressed  in  terms  of  per  cent,  by 
weight  of  iodine  absorbed ;  an  iodine  number  of  185  therefore  signi- 
fies that  the  oil  will  absorb  185  per  cent.,  or  almost  twice  it  own 
weight  of  iodine. 
Paint  and  oil  chemists  become  so  familiar  with  the  relative  iodine 
values  that  an  oil  is  instinctively  classified,  at  least  to  some  extent, 
as  slow  or  quick  drying,  as  soon  as  its  iodine  number  is  given. 
These  iodine  numbers  will  vary  slightly,  even  for  the  same  oil, 
depending  on  when  the  seed  was  gathered,  where  it  was  grown,  etc., 
at  least  in  the  case  of  linseed  and  soya  bean  oils. 
The  iodine  values  of  the  various  drying  oils,  with  the  highest 
given  first,  range  in  order  roughly  as  follows : 
Oil.  Jodine  Number. 
Perilla    190-212 
Linseed    175-200 
Menhadden  fish    155-175 
China  wood    150-170 
Candlenut  or  Lumbang    135-165 
Poppyseed   135-145 
Soya  bean   120-140 
These  represent  pretty  nearly  the  extreme  variation,  although  T 
have  seen  a  sample  of  lumbang  oil,  probably  impure,  which  showed 
the  extremely  low  iodine  number  of  115. 
The  half  hundred  odd  samples  of  linseed  oil,  representing  ship- 
ments received  in  1918  by  John  Lucas  &  Co.,  ranged  from  182.3 
minimum  to  185  maximum  iodine /value".  Since  the  specifications 
of  the  American  Society  for  Testing  Materials  require  that  pure  raw 
linseed  oil  from  North  American  seed  shall  show  a  minimum  iodine 
value  of  not  less  than  180,  all  of  the  above  shipments  represented 
pure  raw  linseed  oil,  as  far  as  could  be  told  from  a  determination 
of  the  iodine  value. 
During  the  same  period,  the  samples  of  soya  bean  all  ranged 
from  132.1-136.9,  indicating  very  good  quality  oil  also,  since  prime 
soya  oil,  of  paint  making  quality,  should  show  an  iodine  number  of 
about  133.  One  sample  of  perilla  oil  showed  an  iodine  number  of 
190.4  and  a  sample  of  lumbang  162.8.  Properly  refined  menhaden 
oil  shows  an  iodine  value  closely  approximating  linseed  oil.  These 
figures  are  given  as  indicative  only,  but  they  serve  to  show  that  all 
of  these  oils  have,  to  some  extent  at  least,  one  of  the  properties  that 
makes  linseed  oil  valuable. 
