Am.  Jour.  Pharm. 
December,  1920. 
The  Theory  of  Percolation. 
859 
the  relative  proportion  of  the  mixed  solvents  is  not  the  same  in  the 
liquid  portion  of  the  perc61ate  as  it  is  in  the  menstruum  and  for 
the  following  reasons:  where  acids  or  glycerin  are  added  to  the 
menstruum  the  addition  is  frequently  made  wholly  to  the  first 
portions  used  to  moisten  the  drug  so  that  the  bulk  of  the  component 
is  found  in  the  primary  fractions  of  the  percolate.  With  hydro- 
alcoholic  menstrua,  which  do  not  usually  vary  to  any  great  extent 
throughout  the  process,  other  conditions  arise  which  may  alter 
the  proportions  of  alcohol  and  water  found  in  the  percolate. 
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Chart  D. 
In  the  first  place  given  a  menstruum  of  high  alcoholic  content, 
the  first  portions  of  the  percolate  will  contain  most  of  the  water  which 
the  drug  originally  held  as  moisture.  This  usually  averages  from  six 
to  ten  per  cent,  of  the  weight  of  the  drug  and  such  a  comparatively 
