Dj'cember,  T?2T  }  The  Theofy  of  PercoMion.  877 
THE  PRODUCT. 
The  product  of  the  process  of  percolation  is  the  percolate.  If 
this  is  subjected  to  any  further  treatment,  with  the  possible  excep- 
tion of  filtration,  some  other  distinct  process  is  involved.  The 
percolate  is  not,  however,  in  condition  for  use  except  in  the  prepara- 
tion of  tinctures,  wines,  certain  elixirs,  or  if  repercolation  has  been 
employed  and,  consequently,  is  frequently  processed  again.  Much 
study  has  been  made  of  the  percolate  and  the  various  methods  of 
treatment  applied  to  it  and,  while  this  aspect  of  the  subject  is  strictly 
outside  the  limits  of  percolation,  the  further  treatment  of  percolates 
is  so  intimately  connected  with  the  extraction  process  that  no  account 
of  the  latter  would  be  complete  without  a  consideration  of  the  fate 
of  the  product. 
In  the  manufacture  of  solid  extracts  the  whole  of  the  percolate  is 
evaporated  nearly  to  dryness;  for  fluidextracts  this  evaporation  is 
confined  to  the  "weak"  percolate  which  is  concentrated  only  as  far 
as  the  volume  of  the  reserved  portion  necessitates.  During  the 
evaporation  of  an  alcoholic  percolate  practically  all  of  the  alcohol 
vaporizes  early  leaving  the  extractive  in  contact  with  hot  water. 
The  temperature  at  which  the  evaporation  is  conducted  may 
affect  the  quality  of  the  ultimate  product  especially  in  such  cases 
where  easily  decomposed  or  rearranged  substances  are  present  and 
particularly  in  acid  liquids.  In  the  latter  case  it  must  be  remem- 
bered that  evaporation  increases  the  concentration  of  the  acid  and 
even  if  it  is  a  weak  acid  it  may  become  concentrated  enough  to 
hydrolyze  glucosides  and  decompose  alkaloids. 
It  is,  therefore,  advisable  to  conduct  all  evaporations  under  re- 
duced pressure  but  is  not  absolutely  necessary  to  do  so  in  every 
case.  A  certain  amount  of  hydrolysis  and  decomposition  will  occur 
no  matter  how  carefully  an  evaporation  is  conducted  even  in  vacuo; 
indeed,  hydrolysis  will  take  place  in  tinctures  of  some  drugs  which 
have  not  been  subjected  to  heat  at  any  stage  of  their  preparation. 
The  changes  which  take  place  in  the  extracted  matter  during 
evaporation  have  been  studied  but  they  are  of  so  complicated  a 
nature  and  involve  so  many  substances  about  which  we  know  little 
that  our  knowledge  of  this  whole  subject  is  only  fragmentary.  We 
have  merely  ^  superficial  idea  of  the  nature  of  substances  as  they 
exist  in  the  living  cell  and  can,  therefore,  state  little  about  the 
changes  which  they  undergo  in  reaching  a  form  in  which  we  may 
investigate  them.    I  think  that  much  time  and  energy  have  been 
