ON  THE  SOLUBILITY  OF  MEDICINAL  PRINCIPLES.  47 
weaker  solutions,  till  the  quantity  left,  when  added  to  the  for- 
mer strong  solution,  will  make  up  the  measure  proposed.  If 
this,  from  inferiority  of  the  materials  used,  is  not  of  the  specific 
gravity  adopted,  it  may  be  further  concentrated. 
If  the  material  to  be  extracted  contains  any  essential  oil  or 
other  volatile  principle,  this  must  first  be  drawn  off  and  set 
aside,  to  be  added  at  the  close  of  the  process,  or  to  be  used  as 
part  of  the  menstruum  in  the  second  part  of  the  process.  This 
is  best  done,  not  by  distilling  over,  but  by  displacing  down- 
wards by  the  vapor  or  alcohol  in  the  vapor  displacement  appa- 
ratus, an  improvement  which  we  now  employ.  But  as  my  ob- 
ject now  is  to  develop  a  general  law  and  its  uses,  and  not  to 
give  particular  formulae,  I  will  not  dwell  longer  on  these  mani- 
pulations. 
In  this  way  alcoholic  solutions  may  be  obtained  of  almost  any 
desired  degree  of  concentration,  for  as  the  solvent  power  of  the 
menstruum  is  no  longer  diminished  by  the  presence  of  water  or 
foreign  matters,  it  becomes,  in  regard  to  many  substances,  lim- 
ited only  by  the  consistence  of  the  solution.  In  general,  how- 
ever, the  concentration  now  generally  adopted  for  the  fluid  ex- 
tracts, in  which  each  fluid-drachm  represents  the  strength  of  60 
grains  of  the  material,  is  a  convenient  one,  and  is  easily  attain- 
able with  almost  every  plant,  but  other  standards  may  be 
adopted,  as  found  expedient. 
We  believe  that  pharmaceutical  preparations  made  in  accord- 
ance with  the  above  hypothesis  will  be  found  superior  in  most 
cases,  to  those  now  in  use. 
In  all  the  formulae  now  in  use,  or  which  I  have  seen  recom- 
mended for  fluid  extracts,  much  of  the  volatile  principles  of  the 
plant  are  dissipated  in  the  concentration  and  lost ;  by  this  plan 
all  are  preserved.  In  those  formulae,  the  removal  of  the  alco- 
hol necessarily  results  in  the  precipitation  of  the  resinous  prin- 
ciples which,  when  such  principles  predominate,  as  in  the  jalap 
and  leptandra,  the  amount  of  sugar  recommended  will  not  keep 
suspended,  nor  the  addition  of  one-fifth  or  one-fourth  of  alcohol, 
as  practised  by  later  manufacturers,  hold  in  solution.  These 
must  therefore  be  removed  at  the  expense  of  the  medicinal 
power  of  the  preparation,  or  else  give  to  it  a  turbid  and  disgust- 
ing appearance.    In  our  proposed  tinctures,  on  the  contrary, 
