rochleder's  proximate  analysis. 
183 
material  is  introduced  necessary  to  fill  them,  the  material  is  covered  with 
spirit,  and  the  completely  fi.lled  bottles  closed  with  glass  stoppers.  After 
standing  24  or  36  hours  in  a  moderately  warm  place,  the  spirit  is  poured 
oS.  As  far  as  possible  this  filtered  extract  is  preserved  in  a  stoppered 
bottle  quite  full,  and  the  material  is  treated  with  a  fresh  quantity  of  spirit, 
which  is  allowed  to  remain  on  the  material  for  examination  24  hours.  The 
extract  thus  obtained  is  employed  for  the  extraction  of  a  second  quantity 
of  material  instead  of  fresh  spirit.  The  extracted  material  is  taken  frum 
the  extracting  vessel  and  expressed  ;  the  expressed  fluid  is  treated  in  the 
same  way  as  that  obtained  by  pouring  off.  In  this  manner  suitably  con- 
centrated extracts  are  obtained.  As  in  Robiquet's  glass  apparatus  for  ex- 
traction a  little  material  can  only  be  introduced  at  once,  and  on  account 
of  the  danger  of  its  breakage  when  operating  with  hot  alcohol,  I  use  an 
extraction  apparatus  of  tinned  iron  plate  for  the  extraction  of  large 
quantities  of  the  substance  for  examination  with  cold  alcohol,  or  the  ex- 
traction of  smaller  quantities  with  hot  alcohol,  with  which  it  is  not  worth 
the  trouble  to  employ  a  still.  This  apparatus  is  so  arranged,  that  it  per- 
mits the  employment  of  hot  or  cold  alcohol  with  equal  facility.  The  appa- 
ratus consists  of  two  concentric  cylinders  joined  together,  which  are  about 
eighteen  inches  high.  The  diameter  of  the  inner  cylinder  is  from  four  to 
five  inches,  and  the  diameter  of  the  outer  one  double  that  size.  Both 
cylinders  are  fastened  together  below  by  an  horizontal  ring  of  tinned  iron 
plate.  The  inner  cylinder  projects  about  an  inch  below.  This  projection 
passes  through  a  ring  which  is  fixed  to  a  funnel.  When  the  funnel  is 
fastened  by  its  spout  to  a  filter  stand,  it  is  only  necessary  to  fix  the  funnel 
to  the  apparatus  for  extraction  firmly  in  a  vertical  position.  The  inner 
cylinder  is  closed  at  the  bottom  with  a  finely  perforated  plate.  The  space 
between  the  two  cylinders  can  be  filled  with  water  at  any  required  tempera- 
ture. From  a  flask  closed  with  a  perforated  cork,  through  which  passes  a 
glass  tube  twice  bent  at  right  angles,  steam  is  conducted  into  the  water 
between  the  cylinders.  Any  required  temperature  can  be  obtained  during 
the  time  of  extraction  by  regulating  the  heat  under  the  flask,  and  thus 
regulating  the  current  of  steam.  To  prevent  the  evaporation  of  the  alco- 
hol added  to  the  material  which  fills  the  inner  cylinder,  into  the  hole  at 
the  bottom  of  which  has  been  inserted  a  loose  layer  of  cotton  wool,  the 
cylinder  is  closed  with  a  tin  cover,  but  not  hermetically  tight.  When  the 
space  between  the  two  cylinders  has  been  filled  with  hot  water,  it  is  closed 
with  a  circular  cover,  which  has  a  perforation  to  admit  the  steam  tube  to 
the  water.  It  is  evident  that  this  tube  must  reach  nearly  to  the  bottom  of 
the  vessel.  To  be  able  to  empty  the  water  conveniently  which  is  placed 
between  the  cylinders,  a  small  cork  is  attached  to  the  external  cylinder  at 
the  bottom  of  its  outer  edge.  When  the  extraction  is  conducted  in  this 
apparatus,  the  alcoholic  extract  passing  through  the  material  is  poured 
back  several  times  on  the  mass  undergoing  extraction,  to  increase  the 
period  of  contact.    When  the  extract  appears  sufficiently  concentrated,  it  is 
i 
