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FILTRATION  UNDER  PRESSURE. 
FILTRATION  UNDER  PRESSURE. 
By  Gustavus  Hinrichs. 
Professor  E.  Bunsen,  of  Heidelberg,  has  recently  devised  a 
very  excellent  improvement  in  the  tedious  but  all  important 
operation  of  filtration.  This  new  method  may  easily  be  applied 
whenever  a  supply  of  water  and  a  good  fall  of  from  10  to  SO  feet 
are  at  disposal.  In  all  towns  with  water  works  and  drains  it  is 
easy  to  put  this  method  into  practice  ;  the  saving  of  time  is  enor- 
mous, for  Bunsen  finished  a  washing  of  chromium  hydrate  in  13 
minutes,  while,  according  to  the  old  process,  7  hours  were  re- 
quired, representing  a  saving  of  97  per  cent,  of  time.  This 
method  will  evidently  be  of  great  use  to  the  pharmacist. 
Bunsen  proved  that  the  rapidity  of  filtration  is  very  nearly 
proportional  to  the  pressure  under  which  it  is  effected.  In  the 
old  way,  when  filtration  is  performed  in  the  atmosphere,  the 
pressure  is  but  very  small.  The  new  method  consists  in  receiv- 
ing the  filtrate  in  a  partial  vacuum,  so  that  filtration  takes  place 
under  a  pressure  more  or  less  nearly  equal  to  that  of  the  atmos- 
phere— 30  to  34  feet,  instead  of  a  few  inches  of  water. 
For  this  purpose  two  things  are  necessary,  a  strengthening  of 
the  filterer  and  the  production  of  a  vacuum. 
For  the  latter  purpose  air  pumps  are  applicable ;  the  vapor  of 
water,  and  especially  the  corrosive  vapors  of  acid,  would  soon 
deteriorate  the  machine.    The  vacuum  is  easiest  produced  by 
means  of  a  stream  of  water  flowing  down  a  vertical  tube  ABC, 
which  latter  is  connected  with  the  receiver  by  a  tube 
^         ^  BD,  which,  at  an  acute  angle,  enters  the  main  tube 
/    ABC.    If  the  tube  BC  be  passed  through  one  or  two 
y        stories  and  connected  below  with  a  drain,  a  very  ef- 
;B  fective  filtration  under  pressure  will  be  possible. 
Even  a  fall  of  8  feet  is  already  quite  effective. 
The  receiver  D  consists  of  a  strong  glass  vessel  to 
receive  the  filtrate,  closed  air  tight  by  means  of  a 
good  stopper  (best  of  rubber)  through  which  the  fun- 
0  funnel  and  a  glass  tube  pass,  likewise  air  tight.  The 
glass  tube  is  connected  with  the  tube  DB  by  means  of 
a  stout  rubber  tube.    In  the  very  accurate  funnel  is  a  circular 
