﻿tlie 
  Porous 
  Plug 
  Experiment, 
  161 
  

  

  at 
  the 
  lower 
  end, 
  and 
  having 
  at 
  the 
  upper 
  end 
  a 
  stuffing-box 
  

   through 
  which 
  passed 
  a 
  hard 
  steel 
  screw 
  for 
  the 
  purpose 
  of 
  

   perforating 
  the 
  bulb 
  when 
  an 
  experiment 
  had 
  to 
  be 
  made. 
  

   The 
  vessel 
  was 
  of 
  such 
  a 
  size 
  that 
  the 
  bulb 
  nearly 
  filled 
  it, 
  

   and 
  any 
  free 
  space 
  could 
  be 
  plugged 
  with 
  cotton-wool 
  if 
  

   necessary. 
  At 
  the 
  bottom 
  of 
  the 
  vessel 
  a 
  fine 
  brass 
  tube 
  

   1 
  mm. 
  in 
  diameter 
  was 
  attached 
  and 
  carried 
  round 
  the 
  

   chamber 
  in 
  the 
  form 
  of 
  a 
  spiral, 
  the 
  length 
  of 
  the 
  tube 
  being 
  

   about 
  1 
  metre. 
  The 
  gas 
  liberated 
  from 
  the 
  bulb 
  had 
  to 
  pass 
  

   through 
  the 
  spiral 
  before 
  escaping 
  into 
  the 
  air, 
  and 
  any 
  heat 
  

   absorlDed 
  by 
  the 
  gas 
  during 
  its 
  expansion 
  would 
  be 
  supplied 
  

   by 
  the 
  liquid 
  contained 
  in 
  the 
  calorimeter. 
  A 
  spiral 
  of 
  

   " 
  manganin 
  " 
  wire 
  was 
  placed 
  in 
  the 
  bottom 
  of 
  the 
  calori- 
  

   meter 
  so 
  that 
  any 
  suitable 
  temperature 
  could 
  be 
  reached 
  and 
  

   maintained 
  by 
  an 
  electric 
  current. 
  A 
  small 
  turbine 
  wheel 
  

   driven 
  by 
  an 
  electromotor 
  served 
  to 
  stir 
  the 
  liquid; 
  the 
  tem- 
  

   peratures 
  were 
  read 
  by 
  a 
  thermometer 
  graduated 
  into 
  gV* 
  

   A 
  second 
  thermometer 
  was 
  placed 
  in 
  the 
  escaping 
  gas 
  in 
  

   order 
  to 
  ascertain 
  whether 
  the 
  gas 
  differed 
  in 
  temperature 
  

   from 
  the 
  liquid 
  in 
  the 
  calorimeter. 
  This 
  was 
  not 
  the 
  case. 
  

   The 
  calorimeter 
  was 
  suspended 
  inside 
  a 
  water-jacketed 
  outer 
  

   vessel, 
  the 
  temperature 
  of 
  which 
  was 
  adjusted 
  by 
  coils 
  of 
  

   wire 
  through 
  which 
  a 
  current 
  was 
  passing. 
  

  

  The 
  mode 
  of 
  conducting 
  the 
  experiment 
  was 
  as 
  follows 
  : 
  — 
  

  

  The 
  bulb 
  containing 
  the 
  gas 
  was 
  weighed 
  and 
  then 
  placed 
  

   in 
  the 
  plug-chamber. 
  At 
  first 
  the 
  bulb 
  was 
  packed 
  round 
  

   with 
  cotton-wool, 
  but 
  experience 
  showed 
  that 
  this 
  was 
  not 
  

   necessary 
  as 
  the 
  small 
  hole 
  pierced 
  in 
  the 
  bulb, 
  and 
  the 
  fine 
  

   brass 
  tube, 
  checked 
  the 
  flow 
  of 
  the 
  gas 
  sufficiently. 
  

  

  In 
  the 
  first 
  series 
  of 
  experiments 
  the 
  temperature 
  of 
  the 
  

   liquid 
  in 
  the 
  calorimeter 
  was 
  raised 
  to 
  about 
  20° 
  C, 
  and 
  a 
  

   cooling 
  curve 
  constructed 
  over 
  a 
  range 
  of 
  temperature 
  of 
  5°. 
  

   A 
  preliminary 
  observation 
  v/as 
  taken 
  of 
  the" 
  alteration 
  in 
  

   temperature 
  produced 
  during 
  the 
  escape 
  of 
  the 
  gas 
  from 
  a 
  

   bulb 
  so 
  that 
  radiation 
  losses 
  might 
  be 
  corrected 
  iu 
  the 
  usual 
  

   way. 
  The 
  actual 
  determination 
  was 
  now 
  made 
  with 
  another 
  

   bulb. 
  The 
  temperature 
  of 
  the 
  calorimeter 
  and 
  its 
  contents 
  

   being 
  adjusted 
  to 
  the 
  required 
  value, 
  the 
  screw 
  was 
  forced 
  

   in 
  and 
  the 
  gas 
  allowed 
  to 
  escape 
  slowly, 
  the 
  rate 
  of 
  escape 
  

   of 
  the 
  gas 
  being 
  regulated 
  by 
  the 
  position 
  of 
  the 
  screw. 
  The 
  

   thermometer 
  was 
  read 
  every 
  minute 
  and 
  a 
  curve 
  plotted 
  of 
  

   the 
  results. 
  The 
  time 
  occupied 
  by 
  an 
  experiment 
  varied 
  

   from 
  5 
  to 
  20 
  minutes, 
  so 
  that 
  even 
  at 
  the 
  shorter 
  time 
  the 
  

   kinetic 
  energy 
  possessed 
  by 
  the 
  escaped 
  gas 
  was 
  small. 
  The 
  

   change 
  of 
  temperature 
  was 
  generally 
  about 
  2°. 
  

  

  After 
  the 
  gas 
  had 
  escaped 
  the 
  bulb 
  was 
  weighed 
  and 
  the 
  

   Phil. 
  Mag. 
  S. 
  6. 
  Vol. 
  18. 
  No. 
  103. 
  Juhj 
  1909. 
  M 
  

  

  