422  ON  ANGOSTURA  BARK  AND  ITS  ESSENTIAL  OIL. 
the  bark  contains  a  substance  which  is  thrown  down  by  caustic 
soda  as  a  yellow  precipitate  from  the  extract  purified  by  means 
of  basic  acetate  of  lead,  freed  from  excess  of  the  lead-salt  by 
sulphuretted  hydrogen,  and  further  purified  by  animal  charcoal ; 
this  precipitate,  however,  undergoes  a  change  even  on  the  filter, 
and  becomes  converted  into  a  blackish-brown  resinous  body. 
By  continued  washing  in  water  this  dissolves  with  a  cherry-red 
color,  but  then  again  changes,  and,  like  a  vegetable  chameleon, 
passes  through  all  sorts  of  colors. 
The  author  was  more  successful  in  the  preparation  of  the 
volatile  oil  of  the  bark.  Four  pounds  of  coarsely  pounded  bark 
were  submitted  to  distillation  with  the  corresponding  quantity 
of  water ;  by  this  means  f  per  cent,  of  essential  oil  were  obtained, 
consequently  more  than  twice  as  much  as  has  hitherto  been 
ascribed  to  it.  Its  properties  and  elementary  composition 
could  therefore  be  more  accurately  studied. 
It  was  impossible  to  distil  the  oil  again  in  the  presence  of 
water,  although  when  set  free  from  the  bark,  it  was  carried  over 
by  the  aqueous  vapors.  An  addition  of  chloride  of  sodium  gave 
no  better  result.  The  aqueous  fluid  was  removed  as  much  as 
possible  by  means  of  a  siphon,  and  the  oil  was  then  left  stand- 
ing for  about  two  days  upon  perfectly  pure,  dry  chloride  of 
calcium,  and  frequently  shaken. 
The  oil  poured  away  perfectly  clear  was  then  distilled  with  a 
thermometer  immersed  in  it  in  a  small  glass  retort  by  means  of 
heated  air,  in  the  small  distilling  apparatus  described  by  the 
author.  At  a  temperature  of  392°  only  a  few  drops  passed 
over,  although  the  author  maintained  the  temperature  for  a 
long  time  at  this  point.  It  was  only  when  the  thermometer 
rose  to  511°  F.  that  a  uniform  ebullition  took  place,  during 
which  the  oil  passed*  without  decomposition.  The  external  ther- 
mometer, that  is  to  say  the  one  which  did  not  sink  into  the 
fluid,  showed  528°  F.  The  residue  in  the  retort  was  of  a  dark 
color ;  the  last  portions  that  passed  were  collected  separately. 
The  pure  oil  was  of  a  pale  wine-yellow  color,  and  possessed  a 
peculiar  aromatic  odor,  resembling  that  of  lovage,  and  a  taste 
which  was  at  first  mild,  but  afterwards  somewhat  acrid.  Its 
spec.  grav.  was  0-934.  Boiling-point  511p  F.,  probably  one  of 
the  highest  boiling-points  for  an  essential  oil. 
