204 
EXPERIMENTS  WITH  PAPER  FILTERS. 
In  the  following  experiments,  the  improved  filter  was  tried 
against  the  plaited  form.  The  improved  filter,  on  account  of  its 
great  strength,  was  allowed  a  funnel  with  a  throat  once  and 
a  half  as  broad  as  that  given  to  the  plaited  filter.  It  would  have 
borne  one  three  times  as  broad. 
1st  trial       121:100  3d  trial,  112:100 
2d     "         125  :  100  4th  "  115  :  100 
The  fifth  trial  was  made  with  a  precipitate  of  sulphate  of  cal- 
cium ;  the  filtrates  were  82  :  100.  Here  the  new  filter  seemed  at 
fault,  but  on  weighing  the  precipitates  collected  they  were  as 
140  :  100.  The  new  filter  being  last  filled,  got  the  thicker  por- 
tions each  time,  while  the  plaited  filter  got  the  weak  top  liquor. 
The  outer  jacket  is  cut  by  folding  the  filter  as  a  plain  filter 
and  taking  out  a  sliver  on  each  edge  ;  repeating  the  process  in- 
creases the  number  of  apertures.  If  the  filters  are  to  be  used 
double,  as  in  broad-throated  funnels,  the  openings  should  extend 
nearly  to  the  vertex  ;  if  they  are  used  single  in  common  funnels 
the  openings  need  not  extend  so  far,  and  the  extreme  point  may 
be  removed. 
A  thick  porous  felt  might  be  used  for  acid  liquors  as  an  outer 
filter.  Cotton  cloth  would  serve  in  alkaline  solutions ;  gun 
cotton  could  be  used  with  either.  If  asbestos  cloth  could  be 
procured  it  would  probably  be  the  best.  It  might  be  cleansed  by 
burning,  and  would  be  unaffected  by  anything  likely  to  be  filtered 
in  quantitative  analysis,  nor  would  it  harm  the  filtrate  when  es- 
timations are  to  be  made  by  permanganate  of  potassium. 
Most  coarse  filter  paper  is  "  stuffed  "  with  mineral  matter  ; 
such  paper  must  of  course  be  leached  in  acidulated  water  before 
being  used  for  quantitative  work,  where  the  filtrate  is  to  be 
saved. 
When  the  precipitate  is  dry,  the  outer  filters  are  thrown  away, 
only  the  fine  inner  filter  being  burned. 
Plaited  and  plain  filters  were  tried  in  like  funnels  ;  calling  the 
plaited  filters  No.  1,  we  had  : 
I.      II.  I.  II. 
1st  trial,       116  :  100  3d  trial,       236  :  100 
2d    "  237  :  100  4th   "        136  :  100 
5th   "  with  sulphate  of  calcium  precipitate,  231  :  100 
the  precipitates  weighed  166  :  100. 
