70 
Improvement  of  the  Burette  Valve,  {^"^-^^^I'S^t'"^' 
2.  The  valve.  Platinum  in  the  form  of  a  smooth  plate  is  not  acted 
jpon  materially  by  any  of  the  solutions  now  in  use  for  volumetrical 
analysis.  The  valve  consists  of  a  platinum  plate  p  of  elliptical  shape, 
I  and  3-16  of  an  inch  being  the  respective  parameters.  Thickness 
p.bout  1-32  of  an  inch.    To  the  centre  of  this  plate  is  soldered  the 
platinum  stem  /,  the  end  of  which  is  pierced  by  an  eye.  The  spring 
made  of  brass  or  German  silver  and  platinated,  is  screwed  to  the 
clamp  and  has  a  fork  at  its  other  end  for  the  insertion  of  the  platinum 
stem  z,  forming  thus  the  hingh  h.  It  carries  a  nut  through  which 
the  [screw  s  passes.    In  order  to  open  the  valve,  the  screw  head  is 
