74 
Filters. 
Am.  Jour.  Pharm. 
Feb.,  1889. 
and  by  a  peculiar  appearance  of  the  precipitate  produced  with  alcohol 
(the  precipitate  is  flocculent  and  collects  in  a  simple  opaque  and  mucous 
mass).  In  common  with  arabin  it  produces  precipitates  with 
diacetate  of  lead,  protochloride  of  tin  and  protonitrate  of  mercury. 
Oxalate  of  Ammonia  detects  in  it  a  calcareous  salt." 
Gmelin's  Chemistry  (Cavendish  edition,  XV.,  209)  states  :  "  Traga- 
canth  jelly  curdles  a  solution  of  bichloride  of  tin ;  according  to  Bostock 
it  forms  a  reddish  precipitate  with  mercurous  nitrate;  according  to 
Pfaff  a  white  precipitate  with  both  mercurous  and  mercuric  nitrate. 
It  is  precipitated  by  alcohol. 
The  use  of  the  word  not  in  the  sentences  quoted  above  from  the 
Pharmacopoeias  was  probably  at  first  an  inadvertent  error,  as  suggested 
by  Oldberg  and  WahPs  "  Companion ; "  but  since  such  errors  are 
likely  to  be  perpetuated  in  print,  it  was  deemed  advisable  to  again  call 
attention  to  it  at  the  present  time. 
ON  FILTERS. 
By  Edo  Claassen. 
It  is  well  known,  that  analytical  work  always  requires  filtering 
paper  of  very  good  quality  ;  in  many  cases  even  the  best  kind  obtain- 
able is  necessary.  The  expenses  caused  by  the  high  price  of  such 
paper  are  not  inconsiderable.  On  account  of  this  fact  and  with  the 
purpose,  probably,  to  reduce  the  cost  of  filters,  Rother  recommended 
the  use  of  pieces  of  paper,  exactly  half  as  large  as  those  usually  taken 
for  filters.  His  filters  have  a  somewhat  unsymmetrical  shape,  unless 
they  are  trimmed  at  last  by  cutting  off  the  useless  and  objectionable 
part.  By  this  operation,  however,  some  paper  is  wasted,  which  is 
entirely  prevented,  if  the  filters  are  made  according  to  the  following  di- 
rections: Patterns  (corresponding  with  the  size  of  the  filters  wanted,  for 
instance  with  such,  having  a  radius  [semi-diameter]  of  12 J,  17 J,  22 J, 
27 J,  32J,  371  421  50,  60,  80,  and  .100  centimeters)  are  constructed 
from  circular  discs  of  tinned  sheet-iron  of  the  same  size  by  cutting  off 
somewhat  more  than  one  half  the  disc  (see  fig.  1.)  through  a  point 
distant  from  the  edge  15,  or  respectively  21,  27,  33,  39,  45,  51,  60, 
72,  96  or  120  centimeters.  The  small  section  of  the  disc,  if  of  no  use 
for  smaller  patterns,  may  be  rejected.  Such  a  pattern  is  placed  on  a 
sheet  of  paper,  a  piece  of  which  is  then  cut  off  by  allowing  the  scissors 
to  go  around  on  the  edge  of  the  tinned  iron.  This  piece  is  now  folded 
once  in  such  a  manner  that  one  part  entirely  covers  the  other  (fig.  2). 
