Am.  Jour.  Pharm. 
June,  1875. 
Improvement  of  the  Burette  Valve. 
271 
turned,  when  the  screw  bolt  comes  into  contact  with  the  glass  tube 
and  forces  the  spring  backwards.  The  valve  plate  assumes  then  a  po- 
sition as  represented  in  figure  allowing  the  full  stream  to  run  straight 
downwards  without  the  least  splashing.  The  capillar  orifice  being  ellip- 
tical, with  its  long  axis  parallel  to  the  stream,  it  is  evident  that  by  re- 
versing the  screw,  the  orifice 
will  close  gradually,  the  lowest  ^ 
point  the  last,  allowing  a  most 
complete  regulation,  and  when 
once  reduced  to  dropping  a  quar- 
ter of  a  turn  of  the  screw  will 
close  totally.  The  only  objec- 
tion to  this  arrangement  of  the 
valve,  which  has  presented  itself 
thus  far,  is  the  delicacy  of  the 
hinge.  Yet  I  have  had  one  in 
use  constantly  for  six  months 
past,  and  it  works  as  satisfac- 
torily as  on  the  first  day.  In 
the  hands  of  beginners  it  may 
come  out  of  order  sooner.  The 
clamp  c  is  made  of  brass  tubing, 
with  the  flanges  ff  and  the  block 
g  soldered  on.  It  is  made  suf- 
ficiently large  to  admit  of  vari- 
ation in  the  diameter  of  the  bu- 
rette tubes,  a  strip  of  paper  being 
used  as  a  filling.  The  delicacy 
of  the  hinge,  and  to  some  extent 
the  cost  of  the  apparatus  (^2.50)  have  prompted  me  to  substitute  a 
simpler  construction. 
Figures  ia  and  2^  represent  this  device. 
The  platinum  plate  is  replaced  by  a  piece  of  pure  rubber  sheeting 
the  thickness  of  strong  paper  by  3-16  of  an  inch,  which  is  attached 
to  the  end  of  the  spring  by  means  of  a  solution  of  rubber.  The  lower 
part  of  the  spring  may  be  rendered  proof  against  chemical  action  by 
galvanic  platinum  plating,  or  by  a  coating  of  rubber.  The  former  is 
certainly  the  best,  but  I  found  by  several  months'  experience  that  a 
spring  coated  with  rubber,  will  resist  the  action  of  standard  acids,  and 
