564  Pharmaceutical  Still  and  Vapor  Condenser.     J  Am'NovUri884arm' 
This  apparatus  is  especially  useful  for  recovering  the  alcohol  from 
dilute  menstrua  and  for  concentrating  alcohol  largely  diluted  for  purifi- 
cation, as  well  as  for  operating  with  solvents  of  larger  volume,  as  in 
the  manufacture  of  resin  of  podophyllum,  berberine  and  hydrastine, 
apiol,  etc.  The  solvent  in  these  processes  contained  in  the  inner  cylin- 
der, and  consisting  of  about  five  gallons  of  stronger  alcohol,  can  be 
recovered  in  sufficient  time  to  continue  percolation  with  it,  making  the 
process  almost  continuous,  and  admitting  of  a  twenty-  or  thirty-gallon 
exhaust  to  be  effected  with  only  about  five  gallons  of  menstruum  above 
that  absorbed  by  the  substance  to  be  exhausted. 
One  of  the  disadvantages  of  this  apparatus  is  the  difficulty 
of  cleansing  it  after  concentrating  the  liquid  to  be  distilled  to  a  certain 
degree,  and  therefore  the  impossibility  of  conducting  4the  evaporation 
to  the  degree  desired.  The  heating  necessary  to  drive  over  the  vapors, 
which  can  only  be  accomplished  at  the  boiling  point  of  the  solvent,  is 
in  many  cases,  especially  in  aromatic  extracts  and  those  containing 
volatile  oils  or  principles,  a  great  disadvantage ;  while,  if  the  evapo- 
ration is  completed  in  some  other  flat  vessel,  considerable  loss  of  the 
solvent  is  experienced — which,  if  alcohol,  ether,  chloroform,  or  carbon 
bisulphide  are  employed — interferes  greatly  with  the  cost  of  the  pro- 
duct. 
The  most  suitable  apparatus  for  recovering  all  the  solvent,  and  one 
admitting  of  rapid  evaporation  without  loss  to  dryness  of  a  solid,  or 
the  desired  density  of  the  residual  evaporate  of  a  fluid  extract,  is  un- 
doubtedly the  "  Hood  Vapor  Condenser,"  which  has  been  in  use  for  some 
time.  It  has  several  claimants  for  the  credit  of  its  origin,  but  I  have 
not  been  able  satisfactorily  to  attribute  it  to  any  one  of  them.  It  is  one  of 
the  most  useful,  if  not  the  most  useful,  solvent  reclaimer  of  any  in  use 
in  the  pharmaceutical  laboratory.  Its  principle  of  projecting  hot 
vapor  against  a  cooled  slanting  surface,  from  which  the  condensed 
liquid  is  recovered  by  a  gully,  is  certainly  not  new,  but  its  application 
offers  advantages  even  beyond  that  principle.  The  vapor  condensing 
in  the  hood  over  the  evaporating  dish,  on  being  condensed,  presents  a 
vacuum  which  greatly  facilitates  evaporation,  and  lowers  the  boiling 
point  of  the  liquid  in  it.  I  had  for  some  time  employed  the 
hood  condenser,  simply  fitted  loosely  on  the  evaporating  dish,  and 
with  most  excellent  results  in  its  operation,  but  found  that  with  ener- 
getic ebullition  the  vapors  would  be  forced  out  between  dish  and  hood, 
occasioning,  when  ether,  benzin,  and  carbon  bisulphide  were  employed, 
