1 8  2  Detection  of  Castor  Oil  in  Copaiba.    { Am^;^rm 
This  wide  standard  may  sometimes  lead  to  an  under-estimation  of  the 
oil  bv  two  or  three  per  cent.,  but  renders  any  over-estimation  impos- 
sible. 
The  actual  process  I  employ  is  as  follows :  3  to  4  grams  of  the 
sample  are  weighed  into  a  clean,  dry  flask,  and  saponified  on  the  water- 
bath  with  50  cc.  of  alcohol  and  a  lump  of  caustic  soda,  weighing  not 
less  than  5  grams.  When  all  is  dissolved  water  is  added,  and  the 
whole  washed  into  a  half- pint  basin  so  as  to  nearly  fill  it,  and  evapor- 
ated to  100  cc.  over  a  low  gas  flame.  Dilute  sulphuric  acid  is  then 
added  until  the  whole  just  becomes  permanently  turbid,  and  then  solu- 
tion of  caustic  soda  is  dropped  in  till  it  just  clears  again.  By  this 
means  a  solution  is  obtained  with  the  least  possible  excess  of  alkali, 
and  with  a  good  amount  of  sodium  sulphate.  The  whole  is  now 
evaporated  to  perfect  dryness1  on  the  water-bath,  stirring  towards  the 
end,  so  that  the  sulphate  may  mix  with  the  soaps  and  produce  an 
easily  pulverulent  residue.  The  residue  is  removed  from  the  basin 
into  a  small,  wide-mouthed,  stoppered  bottle,  and  treated  with  70  cc. 
of  ether-alcohol,  and  well  shaken  up.  As  soon  as  it  is  fairly  settled 
the  fluid  is  filtered  off  through  a  quick  filter,  and  this  is  repeated  with 
two  successive  quantities  of  70  cc,  making  210  cc.  in  all  of  the  sol- 
vent used.  The  residue  in  the  bottle  and  on  the  filter  now  consists  of 
sodium  oleate  and  sulphate  if  the  balsam  be  impure,  and  of  the  latter 
only  if  pure,  with  a  little  trace  of  the  insoluble  resin  soap  already 
referred  to.  The  contents  of  the  bottle  and  filter  are  then  dissolved 
in  warm  water,  and,  after  heating  until  all  smell  of  ether  is  gone,  the 
whole  is  boiled,  freely  acidulated  with  hydrochloric  acid  and  set  to  cool. 
If,  when  cold,  nothing  but  a  few  specks  of  brown  resin  should  rise  to 
the  surface,  the  balsam  is  pure,  but  if  an  oily  layer  be  formed,  it  is 
adulterated,  and  the  smell  of  the  separated  oleic  acid  will  at  once 
determine  whether  it  is  actually  castor  oil  or  not.  In  the  case  of  the 
presence  of  oil,  two  grams  of  pure  and  dry  white  wax  are  added,  and 
the  whole  heated  till  the  wax  melts  with  the  oleic  acid.  On  cooling  a 
solid  cake  is  formed,  which  is  detached  from  the  side  of  the  beaker 
and  the  fluid  below  passed  through  a  filter.  The  cake  is  once 
more  melted  in  boiling  water,  cooled,  detached,  dried  by  gentle 
pressure  in  blotting  paper,  put  into  the  water  oven  in  a  weighed 
1  The  best  way  to  insure  absolute  dryness  is  to  moisten  the  apparently  dry  residue 
with  a  few  drops  of  absolute  alcohol  and  again  dry. 
