﻿71 
  

  

  150 
  

  

  Prof. 
  Kuenen 
  and 
  Mr. 
  Robson 
  on 
  

  

  — 
  less 
  than 
  lialf-a-pound 
  for 
  a 
  complete 
  set 
  of 
  experiments 
  

   lasting 
  for 
  two 
  or 
  three 
  hours. 
  

  

  2 
  The 
  Pressure 
  Apparatus. 
  — 
  The 
  substances 
  prepared 
  and 
  

   purified 
  by 
  methods 
  described 
  in 
  former 
  papers 
  * 
  were 
  

   inclosed 
  in 
  the 
  glass 
  tube 
  of 
  a 
  Ducretet-apparatus. 
  The 
  part 
  

   of 
  this 
  tube 
  which 
  projects 
  outside 
  was 
  bent 
  twice 
  at 
  right 
  

   angles 
  so 
  as 
  to 
  have 
  its 
  top 
  turned 
  down. 
  This 
  top 
  part 
  

   passed 
  through 
  the 
  stopper 
  of 
  the 
  vacuum-vessel 
  and 
  was 
  

   immersed 
  in 
  the 
  low-temperature 
  liquid. 
  

  

  3. 
  The 
  Pressure-Gauges. 
  — 
  Three 
  gauges 
  — 
  (1) 
  an 
  open 
  

   mercury-gauge 
  reading 
  from 
  1 
  up 
  to 
  4 
  atmospheres 
  ; 
  (2) 
  a 
  

   closed 
  gas-gauge 
  with 
  a 
  range 
  of 
  from 
  3 
  to 
  30 
  atmospheres; 
  

   and 
  (3) 
  a 
  closed 
  gas- 
  gauge 
  reading 
  from 
  25 
  atmospheres 
  

   upwards, 
  were 
  used. 
  

  

  In 
  a 
  former 
  paper 
  f, 
  describing 
  experiments 
  in 
  which 
  the 
  

   same 
  gauges 
  were 
  used, 
  it 
  w 
  r 
  as 
  stated 
  that 
  the 
  two 
  closed 
  

   gauges 
  — 
  at 
  that 
  time 
  filled 
  with 
  dry 
  air 
  — 
  showed 
  a 
  difference 
  

   of 
  *7 
  per 
  cent, 
  at 
  25 
  atmospheres. 
  It 
  was 
  discovered 
  later 
  

   that 
  some 
  change 
  had 
  taken 
  place 
  in 
  the 
  high-pressure 
  

   gauge, 
  and, 
  on 
  taking 
  it 
  out 
  of 
  its 
  pressure 
  cylinder, 
  it 
  was 
  

   found 
  that, 
  owing 
  probably 
  to 
  the 
  oxidation 
  of 
  the 
  mercury, 
  

   the 
  volume 
  of 
  the 
  air 
  had 
  diminished 
  by 
  an 
  amount 
  sufficient 
  

   to 
  account 
  for 
  the 
  above 
  difference. 
  The 
  high-pressure 
  gauge 
  

   w 
  r 
  as 
  then 
  filled 
  with 
  dry 
  nitrogen, 
  and 
  its 
  behaviour 
  was 
  found 
  

   to 
  be 
  perfectly 
  satisfactory. 
  We 
  would 
  advise 
  those 
  who 
  have 
  

   to 
  use 
  a 
  high-pressure 
  gas-gauge 
  to 
  take 
  the 
  comparatively 
  

   small 
  trouble 
  of 
  filling 
  it 
  with 
  atmospheric 
  nitrogen 
  instead 
  

   of 
  with 
  air. 
  

  

  The 
  degree 
  of 
  agreement 
  between 
  the 
  high-pressure 
  

   nitrogen-gauge 
  and 
  the 
  low-pressure 
  air-gauge 
  may 
  be 
  judged 
  

   from 
  the 
  following 
  table 
  : 
  — 
  

  

  Low-pressure 
  Gauge. 
  

  

  High-pressure 
  Gauge. 
  

  

  Difference. 
  

  

  25-83 
  

  

  25-86 
  

  

  I 
  

   -•03 
  

  

  26-04 
  

  

  25-99 
  

  

  -f-05 
  

  

  26-48 
  

  

  26-50 
  

  

  -•02 
  

  

  31-44 
  

  

  31-41 
  

  

  + 
  •03 
  

  

  39-67 
  

  

  39-70 
  

  

  . 
  --03 
  

  

  * 
  Phil. 
  Mag-. 
  [5] 
  xl. 
  pp. 
  173-194 
  ; 
  xliv. 
  pp. 
  174-199. 
  

   f 
  Phil. 
  Mag. 
  [6] 
  xlviii. 
  p. 
  180. 
  

  

  