Amka?ch' iP9i5rm* }         Cineol  in  Oil  of  Eucalyptus.  105 
We  have  examined  a  number  of  oils  both  by  the  "  original  "  and 
"  modified  "  Resorcinol  Methods,  and  have  reserved  our  criticism 
of  these  for  the  latter  part  of  our  paper. 
Many  a  chemist's  patience  has  been  sorely  tried  by  the  phos- 
phoric acid  method  of  separating  cineol,  as  outlined  in  the  U.  S.  P. 
VIII ;  and,  therefore,  the  resorcinol  method,  as  proposed  originally 
by  Schimmel  &  Co.  and  as  described  in  the  last  edition  of  Gilde- 
meister  &  Hoffmann's  "  Volatile  Oils,"  seemed  to  afford  an  easy 
and  accurate  means  of  estimating  cineol.  However,  it  became  evi- 
dent at  the  first  application  of  this  method  that  the  new  process 
was  not  above  suspicion,  especially  when  some  eucalyptus  oils, 
persistently  refusing  to  form  a  semi-solid  precipitate  with  phos- 
phoric acid,  showed  unusually  high  cineol  content  when  assayed 
by  the  resorcinol  method. 
The  logical  idea  then  suggested  itself  of  trying  arsenic  acid 
instead  of  phosphoric  acid,  with  a  view  of  obtaining  a  more  stable 
addition  product,  and  the  results  so  obtained  exceeded  our  expecta- 
tions. Later,  a  search  through  the  literature  revealed  the  fact  that 
the  idea  was  not  original  with  us,  since  cineol  arsenate  became  the 
subject  of  a  patent  as  early  as  June  20,  1901  (German  Patent  No. 
132606,  U.  S.  Patent  No.  705545),  and,  according  to  Thorns  & 
Molle  (Arch,  der  Pharmazie,  242  (1904),  p.  172),  they  used  arsenic 
acid  in  February,  1901,  for  the  purification  of  cineol,  as  well  as 
for  its  separation  from  various  fractions  of  the  oil  of  bay  laurel. 
Nevertheless,  we  justly  claim  the  credit  for  being  the  first  to  apply 
arsenic  acid  to  the  quantitative  estimation  of  cineol. 
We  found  that  by  adding,  approximately,  an  equal  volume  of  an 
85  per  cent,  solution  of  arsenic  acid  to  cineol  a  white,  solid,  crystal- 
line substance  resulted,  which  is  sufficiently  stable  to  permit  handling 
it  in  the  air,  and  which  is  decomposed  by  hot  water  into  its  com- 
ponents ;  that  is,  cineol  and  arsenic  acid.  A  compound  obtained  by 
mixing  equimolecular  quantities  of  cineol  (152.98)  and  arsenic  acid 
(140.9)  was  tested  for  its  stability  when  exposed  to  air  at  ordinary 
room  temperature  with  the  following  result : 
5  hours  in  open  air,  temperature  250  C  Loss,  2.9  per  cent. 
22  hours  in  open  air,  temperature  250  C  Loss,  6.0  per  cent. 
29  hours  in  open  air,  temperature  250  C  Loss,  7.0  per  cent. 
45  hours  in  open  air,  temperature  25 0  C  Loss,  8.4  per  cent. 
69  hours  in  open  air,  temperature  25 0  C  Loss,  9.6  per  cent. 
