﻿BAROMETER 
  GAGE 
  EUDIOMETER. 
  391 
  

  

  inches 
  ; 
  and 
  employing 
  an 
  excess 
  of 
  hydrogen 
  when 
  the 
  quantity 
  of 
  

   oxygen 
  is 
  to 
  be 
  ascertained, 
  and 
  an 
  excess 
  of 
  oxygen 
  when 
  the 
  quan- 
  

   tity 
  of 
  hydrogen, 
  or 
  hydrogen 
  and 
  carbon, 
  are 
  in 
  question 
  ; 
  the 
  excess 
  

   in 
  either 
  case, 
  being 
  made 
  equal 
  to 
  the 
  difference 
  between 
  twenty-seven 
  

   inches, 
  and 
  the 
  height 
  of 
  the 
  Torricellian 
  column. 
  With 
  this 
  precaution, 
  

   the 
  quantities 
  introduced 
  or 
  withdrawn, 
  will 
  always 
  be 
  to 
  each 
  other 
  

   as 
  the 
  changes 
  which 
  they 
  produce 
  in 
  the 
  column 
  of 
  mercury 
  in 
  the 
  

   gage 
  tube. 
  The 
  rise 
  of 
  the 
  mercury 
  in 
  the 
  tube, 
  will 
  cause 
  the 
  sur- 
  

   face 
  of 
  it 
  in 
  the 
  receptacle 
  D 
  to 
  be 
  lower 
  ; 
  but 
  the 
  breadth 
  of 
  this 
  ves- 
  

   sel 
  is 
  so 
  great, 
  and 
  the 
  descent 
  of 
  the 
  mercurial 
  surface 
  in 
  it 
  is 
  so 
  

   inconsiderable, 
  that 
  no 
  error 
  worthy 
  of 
  attention 
  is 
  thus 
  created. 
  

  

  I 
  ought 
  to 
  mention, 
  that 
  the 
  cavity 
  of 
  the 
  gage 
  tube 
  ought 
  to 
  be 
  so 
  

   small 
  in 
  proportion 
  to 
  that 
  of 
  the 
  receiver, 
  as 
  to 
  create 
  no 
  error 
  worthy 
  

   of 
  attention. 
  

  

  Description 
  of 
  the 
  Galvano 
  Ignition 
  Apparatus. 
  

  

  An 
  iron 
  cylinder, 
  of 
  about 
  an 
  inch 
  in 
  bore, 
  includes 
  another 
  concentric 
  

   cylinder, 
  or 
  tube 
  of 
  glass. 
  A 
  platina 
  wire, 
  which, 
  by 
  being 
  made 
  the 
  

   subject 
  of 
  a 
  galvanic 
  discharge, 
  is 
  employed 
  to 
  ignite 
  the 
  gaseous 
  mix- 
  

   ture, 
  occupies 
  the 
  cavity 
  of 
  the 
  glass. 
  Opposite 
  to 
  it, 
  two 
  openings 
  are 
  

   made 
  in 
  the 
  iron, 
  which 
  serve 
  for 
  windows, 
  enabling 
  the 
  operator 
  to 
  

   see 
  the 
  progress 
  of 
  the 
  ignition, 
  and, 
  consequently, 
  to 
  know 
  when 
  to 
  

   break 
  the 
  galvanic 
  circuit, 
  in 
  order 
  to 
  avoid 
  fusing 
  the 
  wire. 
  

  

  Method 
  of 
  Operating. 
  

  

  In 
  the 
  engraving, 
  a 
  leaden 
  tube 
  is 
  represented 
  as 
  making 
  a 
  commu- 
  

   nication 
  between 
  the 
  gage 
  tube 
  and 
  the 
  cavity 
  of 
  the 
  iron 
  bottle, 
  

   through 
  one 
  of 
  the 
  valve 
  cocks. 
  Let 
  it 
  be 
  supposed 
  that, 
  by 
  means 
  

   of 
  other 
  valve 
  cocks 
  and 
  tubes, 
  like 
  communications 
  with 
  an 
  air 
  pump, 
  

   and 
  one 
  or 
  more 
  reservoirs 
  of 
  gas, 
  are 
  under 
  the 
  control 
  of 
  the 
  opera- 
  

   tor. 
  

  

  In 
  order 
  to 
  analyze 
  the 
  atmosphere, 
  he 
  should 
  have 
  at 
  his 
  command 
  

   a 
  communication 
  with 
  a 
  bell 
  glass 
  containing, 
  over 
  water, 
  a 
  mixture 
  

  

  