^'"j^'n^'iSs^''"'"}        Terpenes  and  their  Derivatives.  307 
and  in  nitric  acid  a  green  solution.  With  ferric  chloride,  the  aqueous 
solution  gives  a  black  coloration,  which  in  dilute  solution  becomes 
violet  on  adding  a  little  sodium  hydrogen  carbonate.  Its  composition 
corresponds  with  the  formula  Ci2H804=2C6H3(OH)3 — 2H2O,  and  it 
is  to  a  certain  degree  analogous  to  phloroglucol. 
TERPENES  AND  THEIR  DERIYATIYES.^ 
By  J.  W.  Beuhl. 
A  comparative  study  of  the  chemical  and  physical  properties  of  the 
terpenes.  A  table  containing  the  boiling  point,  rotation,  density  d,  re- 
fractive index  for  the  C  line  n,  specific  refraction  — ^  ^ —  a^^ri 
'    ^  (n^  +  2)d'  ^'^^ 
^2  p 
molecular  refraction  —          —  (P  being  the  molecular  weight),  of  a 
number  of  the  best  known  terpenes,  has  been  compiled  from  the  data 
of  different  observers.  The  terpenes  are  thus  divided  into  eight 
groups,  similar  to  those  given  by  Wallach  (Am.  Joujr.  Phar.,  1887,  p. 
61i;,)  phellandrene  and  terpinene  coming  under  the  heading  laurene, 
and  menthene  and  sesquiterpene  forming  an  extra  group.  These 
groups  are  : 
1.  Citrene  (limonene),  boiling  point  172 — 179°,  the  differences  pro- 
bably due  to  impurities  in  the  specimens  examined.  Dextro-rotatory. 
Sp.  gr.  0*846.  Refractive  index  1*47.  Specific  refraction  0*328. 
Absorbs  2  mols.  HCl,  the.  resulting  product  being  identical  with  the 
similar  product  from  dipentene,  and  giving  the  latter  and  not  citrene 
when  the  hydrogen  chloride  is  removed  by  means  of  aniline.  From 
this,  and  the  formation  of  a  tetrabromide  melting  at  104°,  the  presence 
of  two  unsaturated  or  double  bonds  is  probable,  as  also  from  the  mole- 
cular refraction  which  agrees  closely  with  that  calculated  for  such  an 
unsaturated  compound. 
2.  Dipentene. — Differs  from  the  above  only  in  being  optically  inac- 
tive and  yielding  a  tetrabromide  melting  at  124°. 
3.  Isopentene. — Dextrorotatory,  differs  only  slightly  from  the  two 
former  in  physical  properties. 
4.  Sylvestrene. — Has  probably  never  been  prepared  in  a  state  of 
^  Berichte  xxi.,  145-179  and  457-477  ;  reprinted  from  Jour.  Chem.  Soc,  April, 
1888,  p.  377,  and  May,  p.  494. 
