kochleder's  proximate  analysis. 
279 
it  has  been  placed  in  a  stopped  bottle  surrounded  with  cold  water.  The 
chloride  of  calcium  dissolves  in  the  alcohol  and  water  present,  and  the 
volatile  oil  which  ivas  dissolved  separates  on  the  saline  solution  as  a  slight 
film,  which  can  be  removed  by  a  pipette,  washed  with  a  little  water,  and 
obtained  pure  by  rectification  with  water.  As  a  strong  bumping  is  una- 
voidable by  boiling  with  a  little  water  in  the  retort,  I  employ  for  this  pur- 
pose a  flask,  and  introduce  with  the  water  and  the  ethereal  oil  some  large 
pieces  of  clean  linen.  This  plan  also  prevents  the  spirting  over  in  rapid 
distillation. 
b. — Examination  of  the  watery  distillate. 
If  the  watery  distillate  has  a  layer  of  oil  on  the  surface  or  at  the  bottom 
which  has  been  examined  in  the  manner  described,  this  distilhite  is  a 
concentrated  watery  solution  of  the  bodies  contained  in  the  layer  of  oil. 
The  method  of  investigation,  when  the  bodies  are  known,  can  be  previously 
determined  with  exactness.  As  the  bulk  of  these  volatile  substances  which 
are  readily  soluble  in  water,  must  be  contained  in  the  distillate,  a  sufficient 
quantity  of  these  bodies  can  be  obtained  from  this  watery  solution  when 
only  a  little  was  present  in  the  separated  oil.  The  volatile  acids,  in  par- 
ticular, which  almost  all  are,  tolerably  soluble  in  water,  can  be  obtained 
in  large  quantity  from  this  fluid;  likewise  the  volatile  bases,  when  present. 
To  obtain  the  volatile  bases  therefrom,  the  distillate  is  mixed  with  a  few 
drops  of  sulphuric  acid,  and  subjected  to  distillation.  The  bases  remain 
as  sulphates  dissolved  in  the  residue  of  the  distillation.  To  separate  the 
acids,  they  must  be  combined  with  a  base,  and  the  liquid  removed  by  dis- 
tillation. Although  potash  or  soda,  as  the  strongest  bases,  have  the  pre- 
ference before  all  other  bases,  as  by  boiling  they  do  not  permit  the  volatile 
acids  to  become  free,  with  which  they  have  been  once  combined,  their 
employment  is  still  limited,  when  besides  the  volatile  acids,  other  volatile 
substances  exist  in  the  distillate  which  by  alkalies  undergo  a  change  in 
the  '  heat  if  a  small  excess  of  such  alkalies  is  present,  or  when  they  are 
rapidly  decomposed  by  the  oxygen  of  the  air  when  in  contact  with  alkalies. 
If  soda  or  potash  is  employed,  care  must  therefore  be  taken  that  no  excess 
of  alkali  is  present,  but  rather  that  a  small  quantity  of  free  acid  remains, 
which  then  clearly  will  not  be  retained,  but  be  distilled  oflF  with  the  water 
and  the  other  volatile  bodies.  The  potash  or  soda  can  be  replaced,  often 
with  advantage,  by  freely  precipitated  carbonate  of  copper,  or  the  hydrated 
oxide  of  copper,  by  magnesia  as  well  as  by  white  lead,  which  has  been 
specially  prepared  by  passing  carbonic  acid  through  subacetate  of  lead, 
and  should  be  applied  in  a  fresh,  moist  condition,  particularly  when  com- 
pound ethers  are  contained  in  the  solution.  When  the  distillate  has 
deposited  no  layer  of  oil,  but  is  clear  or  only  slightly  turbid,  recourse  must 
be  had,  as  already  mentioned,  to  cohobation.  But  as  with  cohobation  a 
tedious  heating  of  the  fluid  with  the  substance  under  examination  is  un- 
avoidable, and  the  possibility  of  forming  decomposition  products  is  thereby 
