APPARATUS  FOR  EVAPORATION  IN  VACUO,  ETC.  349 
bark,  and  leaves,  which  are  always  found  in  the  latter ;  and, 
finally,  that  it  has  precisely  the  same  medicinal  action  as  natural 
flake  manna. 
A  cursory  glance  at  this  fictitious  flake  manna  would  lead  to 
the  conclusion  of  its  being  the  finest  natural  flake  manna,  from 
which,  indeed,  the  public  would  not  readily  distinguish  it,  but 
closer  inspection  reveals  certain  obvious  diflerences.  When 
broken,  no  crystals  of  mannite  are  to  be  seen  in  the  interstices ; 
there  is  an  absence  of  the  peculiar  bitter  taste  and  of  the  odor 
characteristic  of  good  manna ;  the  fictitious  manna  is  cleaner, 
lighter,  more  uniform  in  color,  and  more  solid,  than  is  usual  with 
natural  flake ;  it  dissolves  more  readily  in  water,  and  makes  a 
clearer  solution,  which,  when  shaken,  does  not  form  a  permanent 
froth.  If  one  part  be  added  to  four  of  rectified  spirit  of  wine, 
and  the  mixture  be  boiled  for  a  few  minutes,  a  residue,  resem- 
bling clarified  honey,  will  be  obtained,  whereas  natural  manna 
treated  in  the  same  way  leaves  a  hard  substance  in  irregular 
masses. 
The  fictitious  flake  manna  aff'orded  me  about  40  per  cent,  of 
mannite ;  natural  manna  in  fine  stalactites,  treated  in  precisely 
the  same  method,  yielded  about  70  per  cent. 
The  crystals  obtained  by  alcohol  were  identical,  whether  the 
artificial  or  natural  drug  were  employed. 
27,  Haymarket. 
— Pharm.  Journ.^  Lond.^  Aprils  1870. 
SIMPLE  APPARATUS  FOR  RAPID  EYAPORIZ ATION  AT 
LIMITED  HEAT,  UNDER  REDUCED  PRESSURE,  WITHOUT 
THE  USE  OP  A  PUMP. 
By  a.  B.  Prescott, 
Assistant  Professor  of  Cbemistry,  etc.,  University  of  Michigan,  U.  S. 
The  pump  is  not  always  at  hand ;  its  use  is  forbidden  for  trans- 
mission of  corrosive  vapors ;  and,  moreover,  the  removal  of 
liquids,  in  form  of  vapor,  against  the  weight  of  the  air  by  mus- 
cular power  is  liable  to  exhaust"  the  operator  more  efi*ectively 
than  it  does  the  material.  I  desire  to  ask  attention  to  some  uses 
of  ordinary  distilling  apparatus,  for  the  production  and  mainte- 
nance of  approximate  vacuum  over  liquids  during  their  vapori- 
