542 
A  Neiv  Filter. 
f  Am.  Jour.  Pharm.. 
\    Dec.  1,  1872. 
slower  ;  but  a  very  fatal  objection  to  the  plain  filter  is  the  superfluous 
fold  which  in  two  thicknesses  lies  under  one-half  the  extended  surface 
of  the  filter.  The  interposition  of  these  two  extra  layers  compels  the 
liquid  to  pass  through  three  thicknesses  of  paper  on  the  half  side  of 
the  extended  filter,  whilst  the  other  half  side  presents  only  a  single 
thickness.  It  is  evident  that  the  two  hidden  layers  are  a  very  appre- 
ciable impediment  to  the  current,  aside  from  the  more  important  fact 
that  the  liquid  will  traverse  this  side  less  rapidly  than  the  other,  and 
thus  occasion  an  imperfect  washing  of  the  precipitate,  or  at  least  pro- 
long the  operation  beyond  reasonable  limits.  The  writer,  recognizing 
the  force  of  this  objectionable  feature,  resorted  to  a  very  simple  modi- 
fication of  the  plain  filter,  which,  while  saving  fifty  per  cent,  of  the 
paper,  removed  all  the  deleterious  defects  of  the  old  form.  This 
new  filter  practically  presents  but  a  single  thickness  of  paper  to  pen- 
etrate, at  the  same  time  preserving  an  even  surface,  equal  in  all  other 
advantages  to  the  plain  filter.  The  strength  and  general  security  of 
the  new  filter  has  been  thoroughly  tested,  and  has  not  failed  in  a 
single  instance.  The  filtrations  are  more  rapid  than  with  the  usual 
form,  and  the  absence  of  the  superfluous  half  sheet  admits  of  a  more 
rapid  drying,  which  is  an  additional  gain  of  the  new  filter.  The  most 
gelatinous,  as  well  as  the  most  compact  and  heavy  precipitates  were 
collected  with  it  from  strongly  corrosive  liquids  with  the  greatest  ease- 
Its  particular  advantages  for  analytical  operations  are  unsurpassed. 
To  make  the  new  filter,  cut  the  circular  disc  of  filtering  paper  in, 
two  through  the  line  of  its  diameter,  take  either  half  disc  and  fold  it 
across  the  line  of  the  radius,  then  turn  down  the  double  edge  of  the 
cut  side  and  fold  it  over  several  times — finally,  run  a  hard,  smooth 
surface  along  the  seam  thus  produced,  to  compress  it,  and  spread  the 
finished  filter  into  an  appropriate  funnel,  first  moistening  it  with  water 
before  the  liquid  to  be  filtered  is  poured  in. 
In  this  connection  the  writer  would  suggest  a  substance  of  great 
utility  in  a  majority  of  analytical  operations.  It  is  the  so-called  "iron 
cuts."  This  material  is  in  regular  pieces  an  eighth  of  an  inch  long, 
with  very  oblique  bases,  and  is  apparently  cut  from  a  very  fine  species 
of  flattened  wire  similar  to  that  from  which  card  teeth  are  made.  It 
is  originally  sold  as  an  improvement  on  iron  filings  for  pharmaceuti- 
cal purposes.  The  writer,  however,  has  employed  it  with  great  suc- 
cess for  its  mechanical  effects  in  analytical  manipulations,  for  which 
purpose  it  is  far  superior  to  sand  or  iron  filings.    Its  cleanliness  and 
