Am.  Jour.  Pharm. 
Sept.,  1893. 
Oil  of  Erigeron  Canadense. 
421 
Similar  results  were  obtained  in  1882  by  Beilstein  and  Wiegand.1 
They  found  the  specific  gravity  to  be  0-8464  at  180  C.  and  that  after 
drying  the  oil  with  metallic  sodium  it  boiled  at  1760  C.  In  1884, 
Wallach2  obtained  a  tetrabromide,  a  limonene  tetrabromide,  which 
melted  at  from  104-1050  C.  In  1887,  A.  M.  Todd3  made  several  in- 
vestigations and  found  the  angle  of  polarization  to  be  —  260  to  —  6o°, 
its  specific  gravity  0-865-0*855,  and  its  boiling  point  at  172-1750  C. 
In  the  same  year  G.  M.  Beringer4  found  the  specific  gravity  to  be 
0-8454  at  15-5°  C.  In  1887,  Fliickiger,5  in  a  communication  from  a 
letter  by  Todd,  states  that  by  the  addition  of  bromine  to  a  cold 
solution  of  the  oil  in  glacial  acetic  acid,  he  obtained  a  crystallized 
compound,  limonene  tetrabromide,  C10H16Br4.  In  September  of 
1887,  Prof.  F.  B.  Power6  found,  in  investigations  which  he  made, 
that  the  boiling  point  was  at  1760  C,  the  specific  gravity  0-8498  at 
1 5°  C.  and  its  composition  to  be  C10H16. 
These  results  are  of  special  value,  as  well  as  those  of  Fliickiger, 
since  the  specimens  of  oil  examined  were  distilled  for  their  purpose 
by  Todd.  As  to  the  question,  which  terpene  it  is,  that  constitutes 
by  far  the  largest  fraction  of  oil  of  Erigeron  Canadense,  the  facts 
rendered  by  the  contributions  catalogued  would  lead  to  the  conclu- 
sion that  it  was  one  of  the  limonenes. 
The  boiling  points  given  by  Vigier  and  Cloez  (175-1760  C.)  by 
Beilstein  and  Wiegand  (1760)  and  by  Prof.  F.  B.  Power  (176°  C.) 
correspond  well  with  the  boiling  point  of  pure  limonene  (175-176°)- 
The  dihydrochloride,  which  Vigier  and  Cloez  obtained,  is  no 
absolute  proof  for  limonene,  though  both  limonenes  will  yield  this 
compound  under  certain  conditions.  This  dihydrochloride  can  also 
be  obtained  from  pinene,  from  terpineol,  from  terpin-hydrate,  and  the 
other  bodies  occurring  in  volatile  oils. 
The  tetrabromides  obtained  by  Wallach,  and  later  by  Fliickiger, 
are  evidently  limonene  tetrabromide,  as  shown  by  their  melting 
1  Berichte  d.  Deut.  Chem.  Ges.,  1882,  p.  2854,  and  Am.  Journ.  Pharm.,  1883, 
P-  372. 
2  Annalen,  227,  p.  292. 
3  Am.  Journ.  Pharm.,  1887,  p.  302. 
4  Ibidem,  p.  285. 
5  American  Druggist,  1887,  p.  201. 
6  Pharmaceutische  Rundschau,  1887,  p.  201. 
