THE  AMERICAN 
JOURNAL  OF  PHARMACY. 
yuiry  1876. 
ON  RAPID  FILTRATION. 
BY  E.  C.  H.  HILDEBRAND. 
Though  much  has  been  said  and  written  on  this  subject,  still  it  does 
not  seem  to  be  exhausted  yet,  not  long  ago  new  suggestions  having 
been  made  in  that  direction.  Viewing  this  matter  from  a  practical 
standpoint,  it  appears  to  me  that  we  should  not  aim  so  much  at  the 
utmost  gain  of  time  in  filtering  and  washing  out  precipitates,  but 
rather  at  a  more  uniform  good  result  of  these  operations.  In  accord- 
ance with  this  view,  the  following  described  apparatus  will  be  found 
both  convenient  and  effective  enough  to  shorten  the  filtering  process,, 
and  the  drying  of  the  filter  and  its  contents  quite  considerably. 
It  is  composed  of  Weil's  filtering  tube,  and  Scheibler's  drop  aspirator,, 
to  which  I  have  added  a  vacuum  regulator.  The  filtering  tube 
(recommended  by  Weil  about  16  or  18  years  ago)  allows  to  filter 
under  a  pressure  of  1  to  2  feet  of  water  column,  without  any  other 
support  of  the  filter  exeept  the  funnel  itself.  It  allows,  further,  to 
filter  into  any  kind  of  receptacle,  which  will  be  found  a  great  conveni- 
ence. On  the  other  hand,  Scheibler's  drop  aspirator,  used  as  a  filter- 
ing pump,  is  by  far  the  most  perfect  one  in  reference  to  the  effect  pro- 
duced by  a  given  quantity  of  water,  while  its  absolute  effect  is  likewise 
very  satisfactory  for  filtering  purposes.  The  vacuum  regulator  is 
intended  to  prevent  the  rarefaction  of  air  surpassing  a  certain  degree. 
Before  entering  into  a  more  detailed  description  of  the  whole  ar- 
rangement, it  may  be  well  to  make  a  few  remarks  about  funnels  and 
filters. 
It  has  been  laid  down  as  a  rule,  that  the  sides  of  a  funnel  should 
have  an  angle  of  inclination  of  60  degrees,  in  which  case  a  filter, 
folded  at  right  angles,  will  fit  exactly  into  the  funnel.  I  found  that  a 
filter  adjusted  into  a  funnel  of  a  more  acute  angle  offers  remarkably 
greater  security  against  breaking,  provided,  of  course,  the  body  of  the 
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