200 
EXPERIMENTS  WITH  PAPER  FILTERS. 
ice  so  that  a  good  navigator,  availing  himself  of  the  openings, 
can  sail  in  or  out  without  serious  delay.  Skill  and  experience 
are  of  course  required, — several  vessels  every  year  paying  the 
penalty  for  the  want  of  knowledge  or  discretion  of  their  masters, 
by  being  caught  and  crushed  in  the  closing  ice-packs.  No  loss 
of  life  has  occurred  as  yet  in  this  trade,  the  ice  affording  a  safe 
refuge  for  the  crew  until  they  are  removed  by  the  Esquimaux, 
or  escape  by  their  boats  to  the  settlement.  The  open  mines  of 
Ivigtout  are  worked  only  during  the  summer  season,  from  May 
to  October,  during  which  time  about  150  men  are  employed.  The 
amount  of  cryolite  now  annually  consumed  in  the  manufacture 
of  soda  alone  is  about  6000  tons.  Oyer  half  a'  million  dollars 
have  been  invested  in  the  extensive  works  of  the  Pennsylvania 
Salt  Manufacturing  Company  at  Natrona,  where  sal  soda,  bi- 
carbonate, alumina,  &c,  are  manufactured  from  this  wonderful 
mineral,  cryolite,  giving  employment  to  over  500  men.  The 
alumina  manufactured  there  is  supplied  to  the  largest  makers  of 
alum  in  this  country;  and  enough  can  be  obtained  from  13,- 
440,000  lbs.  of  cryolite  to  produce  all  the  alum  consumed  in  the 
United  States.  The  various  manufactures  from  cryolite  have  a 
market  value,  at  present  gold  rates,  of  over  one  and  a  half 
million  dollars  per  annum. 
Philadelphia,  January,  1868. 
EXPERIMENTS  WITH  PAPER  FILTERS. 
By  Charles  E.  Avery, 
Student  in  the  Massachusetts  Institute  of  Technology. 
The  filter  most  commonly  employed  in  analytical  laboratories 
is  a  circular  piece  of  paper  folded  twice  upon  itself  into  the  form 
of  a  quadrant,  and  supported  on  a  glass  funnel  with  straight 
sides.  This  filter,  though  commendable  in  so  far  as  it  is  capable 
of  supporting  the  weight  of  a  considerable  column  of  liquid 
without  breaking,  is  objectionable,  inasmuch  as  liquids  cannot 
pass  through  it  so  rapidly  as  is  desirable.  Since  at  almost  every 
point  the  paper  is  in  close  contact  with  the  glass,  but  little  of 
the  liquid  can  flow  off  between  the  filter  and  the  sides  of  the 
funnel. 
Several  schemes  have  at  various  times  been  proposed  for 
