Am.  Jour.  Pharm.  \ 
March,  1915.  J 
Cineol  in  Oil  of  Eucalyptus. 
in 
could  not  be  argued,  therefore,  that  lower  results  obtained  by  our 
method  could  be  due  to  the  solubility  of  cineol  in  water. 
We  have  adduced  sufficient  proof  to  show  that  the  solubility  of 
certain  constituents  of  cineol-bearing  oils  must  necessarily  lead  to 
a  higher  than  actual  cineol  content  when  estimated  even  by  the 
modified  resorcinol  method;  it,  therefore,  becomes  superfluous  to 
discuss  the  total  lack  of  reliability  of  the  original  resorcinol  method 
in  the  form  proposed  for  the  inclusion  into  the  forthcoming  edition 
of  the  U.  S.  Pharmacopoeia.  Some  oils,  such  as  eucalyptus  amygda- 
lina,  may,  when  assayed  by  this  method,  be  accepted  as  a  U.  S.  P. 
oil  of  eucalyptus,  especially  if  a  small  quantity  of  cineol  were  added 
to  them.  Likewise,  oils  rich  in  oxygenated  constituents  may  be 
freed  from  a  large  proportion  of  their  cineol  content  by  freezing 
and  then  offered  in  commerce  as  a  U.  S.  P.  product. 
Schimmel  &  Co.,  in  introducing  the  modified  resorcinol  method, 
assume  that  the  fraction  of  oil  of  eucalyptus  distilling  between  1700 
and  1900  carries  all  of  the  cineol  contained  in  the  oil.  We  admit 
that  such  an  assumption  may  be  correct  in  the  majority  of  oils  ;  we 
have  encountered,  however,  some  oils  in  which  the  presence  of 
cineol  was  proven  in  portions  distilling  either  below  170  or  above 
1900  C.  (see  table,  oils  No.  5,  No.  17,  No.  18)  ;  in  such  oils,  there- 
fore, a  certain  portion  of  cineol  would  not  be  included  into  the 
estimation.  Thus,  while  the  modified  method  is,  in  a  way,  an  im- 
provement on  the  original  method,  yet,  at  the  same  time,  it  intro- 
duces a  new  source  of  error. 
Among  eighteen  samples  of  cineol-bearing  oils  we  found  only 
one  in  which  concordant  results  were  obtained  by  the  resorcinol 
and  arsenic  acid  methods  (see  table,  oil  No.  18).  We  regard  this 
single  exception  as  a  final  and  conclusive  proof  of  the  unreliableness 
of  the  resorcinol  method  in  general,  and  of  the  superiority  of  the 
arsenic  acid  method. 
Summary. 
1.  Arsenic  acid  forms  with  cineol  an  addition  compound  which  is 
sufficiently  stable  for  all  practical  purposes. 
2.  While  the  arsenic  acid  method  cannot  be  included  among  those 
scientifically  exact  methods  which  give  results  varying  only  slightly 
even  in  the  hands  of  a  novice,  nevertheless,  we  are  convinced  that 
this  method  is  superior  to  any  method  yet  proposed  for  the  deter- 
mination of  cineol,  being  directly  applicable  to  all  cineol-bearing  oils, 
