﻿394 
  

  

  OF 
  AN 
  IMPROVED 
  BAROMETER 
  GAGE 
  EUDIOMETER. 
  

  

  When 
  hydrogen 
  is 
  employed 
  to 
  analyze 
  the 
  air, 
  it 
  should 
  be 
  the 
  last 
  

   admitted 
  ; 
  since 
  otherwise 
  it 
  is 
  liable, 
  from 
  its 
  lightness, 
  to 
  pre-occupy 
  

   the 
  cavity 
  in 
  which 
  the 
  platina 
  wire 
  is 
  situated 
  ; 
  so 
  that 
  some 
  time 
  

   would 
  be 
  required 
  for 
  its 
  sufficient 
  admixture 
  with 
  atmospheric 
  oxygen 
  

   to 
  constitute 
  a 
  combustible 
  mixture. 
  

  

  In 
  this 
  mode 
  of 
  operating, 
  when 
  the 
  apparatus 
  is 
  once 
  well 
  arranged, 
  

   the 
  analysis 
  of 
  the 
  air 
  may 
  be 
  repeated 
  as 
  often 
  as 
  desired, 
  and 
  after 
  

   any 
  interval 
  of 
  time. 
  

  

  of 
  which 
  the 
  ignition 
  of 
  the 
  platina 
  wire, 
  and 
  consequent 
  inflammation 
  of 
  the 
  gaseous 
  mixtures 
  

   are 
  accomplished. 
  There 
  are 
  two 
  reservoirs, 
  one 
  of 
  glass, 
  fig. 
  1, 
  the 
  other 
  of 
  lead, 
  fig. 
  2 
  ; 
  the 
  

   latter 
  being 
  about 
  fifty 
  times 
  as 
  large 
  as 
  the 
  other. 
  

  

  As 
  there 
  is 
  a 
  perfect 
  identity 
  in 
  principle 
  of 
  the 
  construction 
  in 
  these 
  reservoirs, 
  an 
  expla- 
  

   nation 
  of 
  one 
  will 
  answer 
  for 
  both. 
  

  

  Suppose 
  the 
  glass 
  jar 
  to 
  contain 
  diluted 
  sulphuric 
  acid; 
  the 
  inverted 
  bell, 
  within 
  the 
  

   jar, 
  to 
  contain 
  some 
  zinc, 
  supported 
  on 
  a 
  tray 
  of 
  copper, 
  suspended 
  by 
  wires, 
  of 
  the 
  same 
  

   metal, 
  from 
  the 
  neck 
  of 
  the 
  bell. 
  The 
  cock 
  being 
  open 
  when 
  the 
  bell 
  is 
  lowered 
  into 
  the 
  

   position 
  in 
  which 
  it 
  is 
  represented, 
  the 
  atmospheric 
  air 
  will 
  escape, 
  and 
  the 
  acid, 
  entering 
  

   the 
  cavity 
  of 
  the 
  bell, 
  will, 
  by 
  its 
  reaction 
  with 
  the 
  zinc, 
  cause 
  hydrogen 
  gas 
  to 
  be 
  copiously 
  

   evolved. 
  As 
  soon 
  as 
  the 
  cock 
  is 
  closed, 
  the 
  hydrogen 
  expels 
  the 
  acid 
  from 
  the 
  cavity 
  

   of 
  the 
  bell; 
  and, 
  consequently, 
  its 
  reaction 
  with 
  the 
  zinc 
  is 
  prevented, 
  until 
  another 
  por- 
  

   tion 
  of 
  the 
  gas 
  be 
  withdrawn. 
  As 
  soon 
  as 
  this 
  is 
  done, 
  the 
  acid 
  re-enters 
  the 
  cavity 
  of 
  the 
  

   the 
  bell, 
  and 
  the 
  evolution 
  of 
  hydrogen 
  is 
  renewed 
  and 
  continued 
  until 
  again 
  arrested, 
  as 
  in 
  

   the 
  first 
  instance, 
  by 
  preventing 
  the 
  escape 
  of 
  the 
  gas, 
  and, 
  consequently, 
  causing 
  it 
  to 
  dis- 
  

   place 
  the 
  acid 
  from 
  the 
  interior 
  of 
  the 
  bell, 
  within 
  which 
  the 
  zinc 
  is 
  suspended. 
  

  

  This 
  engraving 
  will 
  convey 
  an 
  

   idea 
  of 
  the 
  calori 
  motor 
  suitable 
  to 
  

   effect 
  the 
  ignition 
  of 
  the 
  platina 
  wire 
  

   in 
  the 
  galvano 
  ignition 
  apparatus 
  

   above 
  described. 
  It 
  should 
  contain 
  

   two 
  galvanic 
  pairs, 
  each 
  consisting 
  

   of 
  two 
  plates 
  of 
  zinc, 
  10 
  X 
  12, 
  alter- 
  

   nating 
  with 
  three 
  of 
  copper. 
  The 
  

   copper 
  plates 
  of 
  one 
  pair, 
  and 
  the 
  

   zinc 
  of 
  the 
  other 
  being 
  soldered 
  to 
  

   a 
  common 
  metallic 
  strip, 
  the 
  other 
  

   plates 
  of 
  zinc 
  being 
  soldered 
  to 
  one 
  

   strip, 
  the 
  copper 
  to 
  another, 
  each 
  

   of 
  the 
  last 
  mentioned 
  strips 
  is 
  fur- 
  

   nished 
  with 
  a 
  gallows 
  screw 
  G 
  G. 
  

   Between 
  these 
  screws 
  and 
  those 
  at 
  

   W 
  W, 
  (see 
  figure 
  in 
  the 
  text) 
  a 
  com- 
  

   munication 
  is 
  made 
  by 
  leaden 
  or 
  

   copper 
  rods. 
  

  

  To 
  complete 
  the 
  circuit, 
  it 
  is 
  only 
  necessary, 
  to 
  depress 
  the 
  handle 
  attached 
  to 
  the 
  pulleys, 
  

   in 
  order 
  to 
  raise 
  the 
  reservoir 
  of 
  diluted 
  sulphuric 
  acid, 
  and 
  thus 
  to 
  cause 
  it 
  to 
  act 
  on 
  the 
  plates. 
  

  

  