184 
eochleder's  proximate  analysis. 
placed  aside,  and  a  fresh  quantity  of  alcohol  employed  for  the  farther  ex. 
traction.  The  latter  weak  tincture  is  used  instead  of  pure  spirit  for  the 
extraction  of  a  fresh  portion  of  the  material,  so  as  to  render  the  extract  as 
strong  as  possible. 
The  farther  treatment  of  the  alcoholic  extract,  whether  prepared  at 
ordinary  temperatures  or  by  heat,  will  be  described  in  the  next  section, 
VI. — Treatment  of  the  material  to  he  examined  ivith  ether. 
The  treatment  of  the  material  with  ether  is  effected  at  ordinary  tempera- 
tures in  Robiqaet's  glass  apparatus  for  extraction,  or  with  large  quantities 
in  such  an  apparatus  made  of  larger  dimensions  of  tinned  iron  plate.  In 
many  cases  it  is  necessary  to  treat  the  material  to  be  extracted  with  ether 
previously  to  macerating  it  in  alcohol.  This  is  the  case  when  free  fatty 
acids  are  contained  in  the  substance  under  examination.  These  acids  are 
even  dissolved  out  with  other  bodies  by  the  exhaustion  of  the  material  with 
cold  alcohol  containing  water.  To  surmount  this  disadvanta^^e,  these  fatty 
acids  mast  be  removed  by  treatment  with  ether.  In  fresh  materials,  the 
presence  of  free  fatty  acids  can  seldom  be  detected.  On  the  contrary,  in 
substances  which  have  been  kept  a  long  time,  they  can  be  frequently 
recognized.  In  these  cases  the  fattj/  acids  result  from  the  decomposition 
of  the  fats  contained  in  the  fresh  material. 
VII. —  Treatment  of  the  material  to  be  examined  with  alcohol  containing  a 
small  qiiantity  of  ammonia  or  potash. 
For  this  purpose  a  small  quantity  of  the  material  is  taken,  and  one  por- 
tion is  macerated  with  alcohol  containing  potash,  and  another  with  alcohol 
containing  ammonia.  The  alcohol  contains  sufficient  alkali  when  to  an 
ounce  of  the  spirit  six  or  eight  drops  of  a  concentrated  aqueous  solution  of 
potash  or  ammonia  have  been  added.  This  operation  must  be  performed 
in  well  stoppered  battles,  which  must  be  quite  full  of  the  material,  but 
lightly  packed.  The  alkaline  spiiit  is  poured  in  until  the  bottle  is  fall  up 
to  the  stopper,  which  is  then  closed.  By  the  admission  of  the  air  an 
oxidation  of  the  dissolved  bodies  would  easily  result.  After  standing 
several  hours  undisturbed,  the  contents  of  the  bottle  are  placed  on  a  linen 
filter  and  gently  pressed.  The  fluid  is  mixed  at  once  with  as  much  hydro- 
chloric acid  as  will  render  it  slightly  acid,  and  it  should  be  observed 
whether  a  precipitate  is  produced  in  consequence  or  not.  AVhen  no  pre- 
cipitate results,  no  farther  proceedings  are  taken  ;  on  the  contrary,  should 
there  be  a  precipitate,  a  larger  quantity  of  the  material  must  be  treated  in 
the  manner  described.  The  method  of  further  examining  those  solutions 
will  be  given  in  the  nest  section. 
To  be  cantiaucd 
