308  Terpenes  and  their  Derivatives.  {^"''ja^.'im^^'^' 
purity,  and  does  not  appear  to  differ  in  any  marked  degree  from  the 
foregoing. 
5.  Pinene. — Boiling  point  155 — 160°.  Sp.  gr.  0'859.  Refractive 
index  1'463.  Specific  refraction  0'320.  The  molecular  refraction  is 
that  of  a  compound  containing  one  double  bond.  This  agrees  with 
the  chemical  evidence,  as  pinene  combines  with  2  mols.  of  bromine 
and  1  mol.  HCl. 
6.  Laurene  and  Menthene. — Boiling  point  173 — 175°.  L^evorota- 
tory.    Resembles  pinene  in  other  respects. 
7.  Camphene. — Solid,  melting  at  47°;  boils  at  156 — 157°.  The 
hydrogen  chloride  derivative  is  very  unstable  and  is  decomposed  by 
water  at  ordinary  temperatures ;  it  is  therefore  probable  that  this  is 
only  a  molecular  compound,  camphene  containing  no  double  bond,  a 
view  supported  by  its  optical  properties. 
8.  Sesquiterpene,  C15H24. — Found  in  volatile  oils  associated  with  the 
terpenes.  Boiling  point  250 — 260°.  Rotation  differs  for  different 
varieties.  From  its  optical  and  chemical  properties  appears  to  contain 
tw^o  double  bonds. 
The  authrr  regards  the  terpenes  as  derivatives  of  paracymene.  For- 
mulae similar  to  those  of  Wallach  (loc.  cit.)  are  proposed  for  citrene, 
dipentene,  pinene,  and  phellandrene,  and  a  discussion  of  the  various 
possible  formulae  for  the  other  terpenes  is  entered  into. 
In  continuation  of  the  author^s  first  paper  the  oxygen-derivatives 
of  the  terpenes  are  discussed.  The  physical  properties  of  these  are 
arranged  in  a  table  similar  to  that  given  in  the  case  of  the  ter- 
penes. 
Menthol,  C10H20O,  is  probably  a  derivative  of  menthene,  with  which 
it  occurs  in  peppermint  oil.  It  is  Isevorotatory,  and  its  molecular  refrac- 
tion shows  that  it  contains  no  double  bond,  and  that  its  oxygen  is 
united  by  single  afiinities.  It  is  a  secondary  alcohol,  and  on  oxida- 
tion yields  the  dextrorotatory  menthone,  CioHigO,  a  ketone,  the  rela- 
tion of  which  to  menthol  is  similar  to  that  of  camphor,  CjoHigO,  to 
borneol,  CioHigO.  By  the  action  of  hydrogen  chloride,  menthol  is 
converted  into  the  compound  C10H19CI.  This,  by  loss  of  HCl,  yields 
hydromenthene,  CioH^g,  from  the  tetrabromide  of  which,  by  the  remo- 
val of  4  mol.  HBr,  paracymene  is  obtained.  Menthol  is  probably 
hydroxyhexahydroparacymene  [Pr  :  OH  =1:3]. 
Cineol,  CioHigO,  contains  neither  hydroxyl  nor  carbony],  and  yields, 
by  loss  of  water,  dipentene  and  also  paracymene.    It  can  form  yery 
