no 
Cineol  in  Oil  of  Eucalyptus. 
J  Am.  Jour.  Pharni. 
1      March,  1915. 
Close,  agreement  of  results  obtained  by  the  arsenic  acid  method 
on  original  oils  with  those  obtained  on  the  distillate,  collected  between 
170  and  1900  C,  speaks  well  for  their  correctness.  An  additional 
argument  in  favor  of  this  contention  is  the  fact  that  these  results, 
from  the  very  nature  of  the  process,  tend  to  be  somewhat  high  rather 
than  low ;  observing,  at  the  same  time,  that  results  yielded  by  the 
modified  resorcinol  method  are  invariably  higher  than  those  obtained 
by  our  method,  we  must  necessarily  conclude  that  the  latter  repre- 
sent more  nearly  the  true  cineol  content  of  an  oil ;  remembering  in 
addition  the  almost  quantitative  yield  of  cineol  from  its  mixture 
with  various  proportions  of  oil  of  turpentine  when  precipitated  by 
arsenic  acid  (see  p.  107),  we  feel  justified  in  stating  that  our  method 
gives  results  which  represent  the  true  cineol  content  within  the 
limit  of  experimental  error,  which  in  this  case  does  not  exceed 
2  per  cent. 
We  regard  the  results  of  our  experiments  in  known  mixtures  of 
cineol  with  oil  of  turpentine  as  conclusive,  and  our  method  as  directly 
applicable  to  all  varieties  of  cineol-bearing  oils,  for  the  reason  that 
in  such  oils  cineol  is  the  only  constituent  precipitated  by  the  arsenic 
acid. 
The  purity  of  cineol,  as  well  as  the  close  concordance  of  results 
obtained  by  our  method  before  and  after  distillation,  shows  that 
oxygenated  constituents  other  than  cineol  are  not  precipitated  by 
arsenic  acid,  since  fractions  distilling  above  1900  C.  carry  most  of 
such  compounds,  and  their  removal  would  have  resulted  in  a  per- 
centage of  cineol  lower  than  that  obtained  in  the  assay  before  dis- 
tillation, if  the  opposite  were  the  case. 
On  the  contrary,  the  numerous  experiments  carried  out  by 
Schimmel  &  Co.  in  assaying,  by  the  modified  resorcinol  method, 
mixtures  composed  of  cineol  and  fractions  of  eucalyptus  oil  dis- 
tilling below  1  jo  and  above  1900,  do  not  prove  the  reliability  of 
this  method,  since  such  mixtures  do  not  contain  the  non-cineol  con- 
stituents distilling  between  170  and  1900  C,  some  of  which  un- 
questionably are  soluble  in  a  50  per  cent,  resorcinol  solution ;  the 
latter  may  be  seen  from  the  fact  that,  in  the  large  majority  of  oils 
examined  by  us,  the  resorcinol  method  (modified)  gave  higher  re- 
sults than  the  arsenic  acid  method. 
An  additional  error  in  the  resorcinol  method  is  contributed  by 
the  solubility  of  oil  of  eucalyptus  in  water,  which  dissolves  from 
4  to  5  per  cent,  of  this  oil,  whereas  cineol  is  almost  insoluble ;  it 
