14 
ON  SOME  PHARMACEUTICAL  APPARATUS. 
soldered  to  the  sides  forming  a  projecting  ledge  about  three  quar- 
ters of  an  inch  above  the  bottom.  The  ring  is  penetrated  with 
six  holes,  -with  threads  cut  in  them,  in  which  fit  pointed 
thumb-screws  with  shoulders.  On  this  ring  fits  a  similar  tinned 
iron  ring  of  slightly  less  diameter  furnished  with  correspond- 
ing holes  of  such  size  that  the  thumb-screws  pass  easily  through 
them  as  far  as  the  shoulders  which  thus  are  capable  of  binding 
the  two  rings  closely  together,  when  screwed  down.  The 
felt  filter  having  been  cut  to  the  diameter  of  the  vessel,  is 
slipped  down  so  as  to  rest  evenly  upon  the  lower  ring  ;  the  upper 
ring  is  then  placed  upon  it  carefully  so  as  to  avoid  any  overlap- 
ping of  the  felt ;  and  then  the  points  of  the  thumb-screws  being 
pushed  through  the  felt  are  securely  screwed  into  the  lower  ring 
which  binds  the  rings  so  closely  as  to  make  a  tight  joint.  The 
lower  vessel  is  also  provided  with  a  stop-  cock  at  /  to  draw  oiF 
the  filtered  oil  when  it  has  accumulated  sufficiently. 
The  apparatus  is  used  in  the  following  manner.  The  stop 
cock  c  being  closed,  the  upper  vessel  is  fitted  in  its  place, 
and  the  tube  joint  e  rendered  tight  by  wrapping  twice  around 
it  a  strip  of  isinglass  plaster  well  moistened.  When  this  is  dry, 
the  upper  vessel  is  filled  with  the  crude  oil,  and  the  stop-cock  e 
opened  that  the  oil  may  flow  into  the  open  space  below  the  filter. 
To  facilitate  the  passage  of  the  oil,  the  apparatus  should  be  sup- 
ported above  a  stove,  or  other  source  of  heat,  so  that  its  tem- 
perature may  rise  to  120  degrees ;  and  in  the  case  of  castor  oil 
this  is  really  necessary  owing  to  its  consistence.  As  the  filtered 
oil  accumulates  in  B,  it  should  be  drawn  off,  as  any  large  amount 
greatly  retards  the  process  by  decreasing  the  force  of  the  col- 
umn bearing  on  the  filter.  The  fact  that  the  filtration  occurs 
from  below  upward  is  esteemed  an  advantage  as  the  tendency  of 
the  impurities  is  to  settle  away  from  the  filtering  surface  and  not 
to  accumulate  upon  and  clog  it. 
An  instrument  of  this  size  properly  attended  should  filter  a 
barrel  of  oil  in  a  day  with  ease,  and  the  whole  arrangement  is 
so  symmetrical  that  it  may  stand  in  the  shop  without  offending 
the  sight  or  interfering  with  other  operations.  The  oil  may 
be  drawn  from  the  vessel  B  directly  into  bottles  if  desired,  or  by 
means  of  a  gum  tube  drawn  over  the  mouth  of  the  cock  it  may 
be  conveyed  into  any  large  receptacle  placed  near  it. 
Believing  that  the  utility  of  an  efficient  and  convenient  ap- 
