^ebSS^T'}     Resins  and  Relations  to  Terpenes.  61 
time  the  iodine  is  all  liberated  and  there  is  left  a  resinous  mass 
composed  chiefly  of  two  substances.  This  resinous  mass  was  sub- 
jected to  distillation  in  vacuo.  The  distillate  obtained  was  a  thick, 
colorless,  stable  oil.  Its  molecular  weight  indicated  a  dipinene. 
It  contained  no  iodine,  and  from  its  remarkable  stability  it  is 
probable  that  the  pinene  radicles  are  doubly  joined  to  each  other. 
By  oxidation  it  forms  an  acid  isomeric  with  abietic  acid.  The 
residue  left  in  the  flask  after  the  dipinene  had  been  removed  was 
also  of  unusual  interest.  It  proved  to  be  a  solid  of  a  light  amber 
color.  It  had  exactly  the  same  melting  point  of  ordinary  rosin. 
Most  of  its  properties  were  also  identical  with  those  of  common 
rosin.  It  proved  to  be  a  tetra  pinene,  and,  owing  to  its  close 
resemblance  to  ordinary  colophonium,  it  has  been  called 
colophonene. 
These  two  condensed  forms,  the  di-  and  the  tetra-pinene  com- 
pounds, have  been  isolated  and  carefully  studied.  Both  are  stable, 
but  may  be  oxidized  to  acids  with  many  of  the  characteristics  of 
the  resin  acids.  A  comparison  of  these  synthetic  compounds  with 
the  natural  resins  is  both  interesting  and  important.  Those  which 
have  been  prepared  and  examined  at  the  present  time  do  not  agree 
in  every  respect  with  the  natural  resin  acids.  This  fact  is  not 
surprising,  however,  as  any  one  of  the  different  groups,  occurring 
in  the  molecule  when  oxidized,  would  give  a  different  acid.  It 
would,  therefore,  be  mere  chance  if  the  synthetic  compounds  should 
be  identical  with  the  common  resin  acid. 
In  summing  up  the  experimental  evidence  in  connection  with 
the  theories  of  the  formation  of  the  resins  and  terpenes  and  their 
chemical  relationship,  the  following  syntheses  may,  under  different 
conditions,  represent  what  takes  place  in  certain  phases  of  plant 
life: 
1.  The  formation  of  the  resins  from  the  simple  aldehydes. 
2.  The  formation  of  the  resins  from  the  complex  aldehydes  or 
carbohydrates. 
3.  The  formation  of  the  resins  from  the  terpenes. 
It  is  not  impossible  that  the  resins  are  formed  by  any  one  of 
the  above  syntheses.  There  are  abundant  reasons  for  believing, 
however,  that  the  synthesis  of  many  of  the  resins  is  intimately 
related  to  the  terpenes,  that  is,  the  terpenes  may  be  first  formed 
from  simple  compounds  as  the  hemiterpenes,  then  converted  into 
