182 
eochleder's  proximate  analysis. 
the  substance,  the  liquid  is  filtered  through  paper.  This  fluid  is  suitable 
for  the  detection  therein  of  some  bodies  which  are  soluble  in  alkaline 
liquids,  but  not  in  water  or  dilute  acids.  Only  when  the  addition  of  dilute 
hydrochloric  acid  produces  a  precipitate  in  this  fluid  is  it  prepared  on  a 
larger  scale  for  the  further  examination  of  the  precipitate.  When  no 
precipitate  results,  it  is  no  longer  employed  for  the  investigation. 
Y .  —  Treatment  of  the  7naterial  io  be  examined  with  alcohol. 
Whether  alcohol  containing  more  or  less  water  is  employed  for  the  ex- 
traction of  the  material,  whether  the  extraction  should  be  conducted  at  an 
ordinary  temperature  or  at  a  boiling  heat,  depends  on  the  properties  of  the 
material  to  be  extracted.  The  operator  must  first  convince  himself  whether 
a  considerable  quantity  of  fat  is  present  or  not.  It  is  easy  to  ascertain 
this  with  certainty.  The  extraction  of  a  small  quantity  of  the  material 
with  ether,  and  tlie  evaporation  of  the  ether,  proves  this.  It  may  be 
readily  observed  whether  the  residue,  after  the  evaporation  of  the  ether, 
contains  much  fat  or  not.  When  the  material  contains  only  a  very  little 
fat,  the  alcohol  should  be  applied  boiling  hot  for  the  extraction.  In  this 
case  a  spirit  of  .825  sp.  gr.  should  be  employed.  If  a  great  quantity  of  the 
fat  is  present  in  the  material,  which  is  the  case  when  by  expression  be- 
tween cold  or  heated  plates  the  chief  bulk  of  the  fat  is  separated,  weaker 
spirit  of  specific  gravity,  between  .850  and  .855,  must  be  employed,  and 
the  extraction  performed  at  an  ordinary  temperature. 
Should  the  material  be  treated  with  hot  alcohol,  and  a  large  quantity 
be  operated  upon,  a  still  is  the  best  for  this  purpose  which  is  provided  with 
an  inner  receptacle  for  the  material  and  the  alcohol.  The  heat  employed 
is  that  of  a  water-bath.  When  the  head  of  the  still  is  affixed,  and  proper 
care  taken  for  cooling  the  distillate,  but  little  alcohol  is  lost,  because  its 
vapor  is  condensed.  If  volatile  substances  exist  in  the  material,  they  pass 
over  simultaneously  with  the  spirit.  Easy  as  it  is  to  separate  volatile 
acids  or  bases  from  the  spirit,  it  is  equally  difficult  to  remove  volatile  oils 
therefrom.  Such  alcohol  is  constantly  again  and  again  used  for  the  extrac- 
tion of  a  fresh  quantity  of  the  same  material ;  in  the  worst  cases  it  can  be 
employed  for  combustion,  Ac.  When  the  spirit  has  acted  sufficiently  long 
on  the  material  to  be  extracted,  the  head  of  the  still  is  removed,  and  the 
receptacle  and  its  contents  together  withdrawn  from  the  still,  then  the 
liquid  is  strained  through  linen,  and  the  material  is  expressed  by  slowly 
increased  pressure.  The  alcoholic  decoction  is  filtered  while  hot  through 
paper,  and  placed  aside  to  cool,  whereby  frequently  bodies  separate  which 
are  more  difficultly  soluble  in  cold  than  in  hot  spirit.  The  extraction  of 
the  materia]  with  cold  alcohol  is  conveniently  performed  in  a  bottle  with 
a  very  wide  mouth,  which  is  furnished  with  a  glass  stopper  well  ground  in. 
It  should  be  of  such  dimensions  that  materials  to  be  introduced  should 
almost  fill  it  when  loosely  inserted  therein.  It  is  better  to  employ  several 
small  bottles  instead  of  one  large  one.    Into  these  bottles  the  quantity  of 
