Am.  Jour.  Pharm.  ) 
December,  1920.  j 
The  Theory  of  Percolation. 
879 
Lloyd  has  said,  "I  must  say  that  it  does  not  seem  probable  that  we 
shall  ever,  by  percolation  alone,  succeed  in  making  a  line  of  perma- 
nent fluidextracts  from  dry  plants.  The  most  important  of  steps 
then,  is  to  adapt  our  menstruum  so  that  it  may  hold  in  solution  the 
medicinal  principles  of  each  plant  and  thus  render  the  precipitate 
which  forms  inert;  for  the  precipitate  will  follow." 
The  known  causes  of  precipitation  are:  variation  in  the  com- 
position of  menstrua  whereby  extracted  matter  obtained  under 
different  conditions  is  introduced  into  a  preparation;  introduction 
of  water  by  evaporation  of  weak  percolates  and  addition  to  the 
reserve;  oxidation  of  soluble  substances  with  the  production  of 
PROF.  JOHN  URI  LLOYD 
Inventor  of  the  Lloyd  extraction  apparatus;  author  of  valuable  papers  on  the 
precipitates  in  fluidextracts. 
insoluble  matters:  changes  of  temperature ;  chemical  changes  within 
the  solution;  the  presence  of  inorganic  matters;  the  presence  of 
minute  particles  of  insoluble  substances  which  at  first  are  invisible 
but  later  agglomerate  and  cause  a  deposit.  It  has  been  shown  that 
light  does  not  cause  precipitation. 
An  interesting  effect  of  precipitation  was  observed  by  Lloyd. - 
He  found  that  there  is  considerable  difference  between  the  alcoholic 
content  of  a  freshly  prepared  fluidextract  and  the  same  preparation 
after  it  has  precipitated.  In  the  case  of  Fldext.  Podophyllum  the 
change  was  from  53  per  cent,  to  65  per  cent.,  in  Jalap,  83  per  cent. 
'  Eclectic  Med.  Cleaner,  3,  505,  (1897);  This  Journal,  Vol.  80.  y),  (1908). 
