43  8  Preparation  of  Extracts  without  Heat.  {AmsIp^*l8P7h7?rm" 
mineral  waters  for  the  purpose  of  facilitating  its  transportation.  I  have 
utilized  the  same  property  for  the  concentration  of  vegetable  juicesT 
and  in  general,  of  aqueous  solutions  of  organic  principles. 
The  results  of  my  observations  have  satisfied  me  that,  when- 
the  water  partially  congeals,  the  dissolved  principles  remain  in  solu- 
tion in  the  mother  liquors,  and  that  two  or  three  congelations  are 
generally  sufficient  for  obtaining  the  solutions  concentrated  enough  to 
finish  the  extract  by  exposure  upon  plates  to  the  heat  of  the  sun  or  of 
a  drying  closet,  heated  to  about  30°C.  (86°F.)  The  extracts  prepared 
by  this  method  accurately  represent  the  properties  of  the  plants,  and 
the  principles  which  are  changed  by  the  influence  of  heat  remain  unal- 
tered ;  even  the  volatile  constituents  are  not  dissipated,  though  most 
of  the  water  be  removed  by  freezing.  Owing  to  the  small  cost  of  the 
necessarv  apparatus,  it  appears  to  me  that  my  process  for  preparing 
extracts  should  be  preferable  even  in  those  countries  where  ice  is  less 
readily  obtainable  than  combustibles. 
Extract  of  conium,  prepared  with  unpurified  juice  by  the  process 
mentioned,  has  preserved  the  characteristic  odor  of  conia,  and  by  dis- 
solving it  in  water  I  have  obtained  a  solution  exactly  representing 
the  juice  of  the  plant  in  appearance  and  properties,  and  giving,  when 
heated,  an  abundant  coagulation,  proving  that  even  albumen  had 
remained  unaltered.  1750  grams  of  cow's  milk,  of  90  B.,  left,  after 
three  congelations,  750  grams  of  a  liquid  having  a  density  of  140,  and 
by  evaporation  in  the  sun  this  left  a  dry  extract  of  milk,  which  again 
formed  that  liquid  on  being  dissolved  in  water.  A  number  of  other 
liquids,  similarly  treated,  gave  corresponding  results,  and  it  seems  to 
me,  therefore,  that  medicinal  extracts  are  best  prepared  by  congelation. 
It  may  be  objected  that  the  vegetable  juices  should  be  previously  puri- 
fied ;  but  it  should  be  remembered  that  coagulated  albumen  always 
encloses  a  considerable  portion  of  the  active  principles,  and  that  the 
heat  necessary  to  effect  the  coagulation  and  the  evaporation  by  means 
of  a  water  bath  is  sufficient  to  change  many  principles  ;  also,  that  the 
extracts  thus  prepared  are  sometimes  inert  or  less  active.  The  careful 
experiments  made  by  Orfila  and  the  clinical  experience  of  others- 
demonstrate  that  extracts  prepared  with  unpurified  juice  are  stronger. 
The  results  of  the  experiments  just  mentioned  will  show  that  my 
process  may  be  advantageously  used  for  the  preservation  of  vegetable 
juices,  which  are  obtained  by  dissolving  the  extract  in  sufficient  water 
