Am.  Jour.  Pharm.  \ 
June,  1875.  J 
Improvement  of  the  Burette  Valve. 
269 
ON  AN  IMPROVEMENT  OF  THE  BURETTE  VALVE. 
BY  GEORGE  A.  KOENIG,  PH.  D. 
[From  a  paper  read  before  the  American  Philosophical  Society ,  Aug.  zist,  1874.) 
The  author  discussed  first  the  merits  and  demerits  of  the  various 
valve  burettes,  constructed  by  Mohr,  Gay-Lussac,  and  others,  and 
then  proceeds  v^ith  the  description  of  a  device,  which  has  realized  his 
expectations  as  to  the  possibility  of  combining  the  advantages  of  Mohr's 
principle  with  universal  applicability  and  convenience  of  handling.* 
I,  The  burette,  I  take  a  Mohr  burette  tube,  as  it  is  furnished  by 
the  trade,  hold  the  inflated  part  of  the  neck  (serving  for  a  hold  to  the 
rubber)  over  a  Bunsen  flame  and  let  it  contract  slowly  at  a  dull-red 
heat,  until  the  channel  has  become  capillar  as  shown  in  figures  i^,  ic 
and  2a  of  the  accompanying  plate.  It  needs  hardly  to  be  remarked, 
that  during  the  process,  the  tube  has  to  be  kept  revolving,  and  allowed 
to  cool  slowly.  The  glass  wall  has  become  very  thick  and  strong,, 
facilitating  the  next  process  of  grinding.  This  is  done  upon  an  ordin- 
ary rotary  grindstone,  in  from  8  to  10  minutes.  I  grind  off  one-half 
of  the  inflation  at  a  steep  angle,  as  shown  in  the  figures.  The  orifice 
is  not  required  to  have  a  definite  size  and  is  naturally  given  by  the 
points  The  grinding  is  continued  until  the  elliptic  section  of  the 
channel  has  come  with  its  lowest  point  from  about  1-16  to  1-8  of  an 
inch  above  the  lowest  point  of  the  inclined  ground  plane.  A  very 
short  practice  affords  sufficient  skill  to  grind  a  very  nearly  plane  surface. 
Absolute  planeity  is  not  required.  The  sides  and  back  are  ground 
next  to  produce  a  point,  which  is  necessary  for  the  letting  out  of  small 
drops  of  liquid.  The  ground  face  stands  at  right  angles  to  the  gradu- 
ation and  may  be  put  either  on  the  right  or  on  the  left  side,  according 
to  the  convenience  of  the  operator.  Figure  ic  represents  a  front 
view  of  the  ground  face,  with  the  capillar  orifice  at  0.  The  size  of 
the  latter  depends  on  the  kind  of  work  which  is  to  be  done  with  the 
burette,  as  it  influences  the  size  of  a  drop.  On  my  20  c.c.  burette, 
divided  into  twentieths,  I  have  a  very  narrow  orifice,  a  drop  correspond- 
ing to  one-half  a  division.  I  use  the  burette  exclusively  for  argentum 
nitrate  solution.  For  ordinary  alkalimetric  work  I  use  a  burette  (50  c.c.) 
graduated  into  one-fifths  and  allow  the  drops  to  equal  one-tenth  cc. 
This  opening  empties  the  burette  in  one  minute  and  a  quarter,  when 
running  at  full  stream. 
The  cuts  illustrating  this  paper  were  kindly  furnished  by  tiie  American  Philo- 
ophical  Society. — Editor  Amer.  Jour.  Pharm. 
