ON  CROTON  OIL. 
409 
tube  is  dropped  into  a  retort  heated  to  redness,  and  containing 
copper  turnings,  or  common  pumice  stone  with  its  pores  filled 
with  metallic  copper.  Pumice  stone  is  thus  prepared  by  being 
immersed  in  a  solution  of  bluestone,  dried,  heated  to  reduce  the 
absorbed  salt  to  oxide  of  copper,  and  finally  reducing  this  in  a 
current  of  hydrogen.  The  obtained  oil  is  farther  purified  as 
stated  above. 
III.  The  Fixed  Products. — The  residue  of  the  distillation  under 
L,  is  a  nearly  colorless  oil,  which  in  contact  with  the  air  is  heated 
to  above  100°  C,  (212°  F.),  at  the  same  time  a  current  of  steam 
is  passed  through  it,  by  which  an  oil  is  obtained  neutral,  odor- 
less and  more  or  less  fluid,  ready  to  go  into  commerce  ;  its 
qualities  may  be  improved  by  one  or  more  repetitions  of  the 
same  process;  the  water  is  driven  off  by  heating  the  oil  to  150° 
C,  (302°  F.) 
The  fixed  resin  oil  may  alsoHbe  treated  in  the  following  man- 
ner :  the  heated  oil  is  several  times  shaken  with  5  per  cent,  of 
its  bulk  of  a  solution  of  caustic  soda  of  36°  Beaume,  from  25  to 
50  per  cent,  of  water  is  then  added,  and  the  whole  heated  to 
boiling  for  several  hours,  taking  care  to  replenish  the  evaporat- 
ing water.  The  oil  is  then  decanted  and  filtered  through  dry 
sand  or  dry  saw-dust  mixed  with  chalk  or  burned  gypsum,  by 
which  process  it  is  obtained  clear. — (Armengaud's  Grenie  Indust. 
Fevr.,  1856— Dingier  s  Polytechn.  Journ.  cxlii,  297-301). 
J.  M.  M. 
ON  CKOTON  OIL. 
By  Thomas  Schltppe. 
The  author  obtained  the  oil  which  he  investigated  by  pressing 
the  crushed  seeds  of  Croton  Tiglium  between  warm  metal  plates, 
after  they  had  been  warmed  in  the  water-bath.  The  oil-cakes 
were  then  broken  up  small  and  extracted  with  alcohol  of  spec, 
grav.  0-848  in  a  displacement  apparatus.  It  appeared  that  the 
alcohol  did  not  dissolve  the  oil,  but  only  displaced  it.  For  the 
purpose  of  this  extraction,  the  author  employed  an  apparatus 
which  enabled  the  alcohol  flowing  off  to  be  distilled  back  again. 
After  it  has  passed  four  times  through  the  seeds,  there  were  two 
