56  Resins  and  Relations  to  Ter penes.     jA£ -,Jour- 
1  \   February,  1913. 
of  unknown  constitution.  Notwithstanding  the  fact  that  less  is 
known  concerning  the  chemical  nature  of  the  resins  than  perhaps 
any  other  group  of  organic  compounds,  they  are  doubtless  the 
oldest  organic  compounds  known  to  man.  They  played  an  im- 
portant part  in  the  chemical  industries  in  the  early  history  of 
mankind.  They  were  used  in  almost  every  phase  of  early  human 
life,  as  lacs,  varnishes,  balsams,  perfumes,  pomades  and  in  the 
art  of  embalming.  They  were  described  by  the  early  alchemists  as 
substances  insoluble  in  water,  generally  soluble  in  alcohol,  and 
for  the  most  part  non-crystallizable.  They  are  the  result  of 
secretive  plant  fluids,  exuding  from  the  plants  and  hardening  in 
the  air.  They  could  not  be  separated  into  their  constituents  by 
any  means  known  to  the  early  chemists,  and  were  therefore  re- 
garded as  single  substances.  As  a  rule,  however,  they  are  mixtures 
of  two  or  more  complex  substances,  a  gum  and  some  volatile 
oil  or  terpene.  They  were  known  as  gum  resins  or  natural  balsams 
and  with  the  terpenes  as  oleoresins.  As  a  result  of  their  non- 
crystalline nature  they  were  generally  excluded  from  the  list  of 
substances  worthy  of  investigation. 
That  there  is  a  close  chemical  relationship  between  the  resins 
and  the  terpenes,  there  can  be  no  doubt,  notwithstanding  the 
fact  that  there  is  comparatively  little  experimental  evidence  to 
prove  the  assertion.  One  of  the  reasons  usually  given  for  the 
assumption  is  based  on  the  fact  that  the  resins  and  terpenes  gen- 
erally occur  together  in  plants.  This  is  by  no  means  important 
evidence,  for  it  frequently  happens  that  entirely  different  groups 
of  organic  compounds  are  intimately  associated  with  each  other  in 
both  plant  and  animal  life. 
Notwithstanding  the  fact  that  considerable  general  industrial 
work  has  been  done  on  the  resins,  especially  those  of  the  pine 
family,  yet  no  one  has  been  able  to  determine  with  certainty  the 
molecular  constitution  of  any  of  them,  not  even  of  abietic  acid, 
the  most  common  and  the  most  important  of  all  of  the  resin 
acids.  Not  only  are  the  structural  formulae  unknown,  but  in  most 
cases  the  empirical  formulae  are  still  in  doubt.  For  instance,  the 
formula  for  abietic  acid  has  been  generally  accepted  as  C20H30O2, 
but  Mach  in  his  dissertation  on  the  acid  gave  to  it  the  formula 
C19H2802.  Absolutely  nothing  is  known  of  its  chemical  constitution. 
Various  theories  have  been  advanced  concerning  the  relation- 
