﻿590 
  Mr. 
  J. 
  Satterly 
  on 
  the 
  Amount 
  of 
  

  

  out 
  as 
  a 
  steady 
  stream 
  and 
  collected 
  in 
  a 
  litre 
  flask. 
  The 
  time 
  

   taken 
  for 
  1 
  litre 
  was 
  taken 
  two 
  or 
  three 
  times 
  and 
  the 
  reading 
  

   of 
  the 
  gauge 
  noted. 
  This 
  was 
  repeated 
  at 
  various 
  speeds, 
  

   and 
  a 
  curve 
  drawn 
  showing 
  the 
  relation 
  between 
  the 
  air- 
  

   current 
  in 
  litres 
  per 
  minute 
  and 
  the 
  gauge-reading. 
  

  

  Three 
  such 
  gauges, 
  denoted 
  by 
  A, 
  B, 
  and 
  C, 
  were 
  set 
  up. 
  

   B 
  was 
  used 
  for 
  some 
  time, 
  but 
  for 
  some 
  reason 
  or 
  other 
  

   proved 
  untrustworthy. 
  It 
  was 
  then 
  rejected 
  and 
  A 
  and 
  C 
  

   only 
  were 
  used. 
  These 
  were 
  calibrated 
  separately, 
  and 
  also 
  

   occasionally 
  compared 
  by 
  putting 
  them 
  in 
  series. 
  They 
  were 
  

   always 
  in 
  good 
  agreement. 
  

  

  (5) 
  The 
  Suction-pump. 
  — 
  When 
  performing 
  the 
  experi- 
  

   ments 
  air 
  was 
  drawn 
  through 
  the 
  tubes 
  by 
  a 
  filter-pump 
  

   fitted 
  to 
  a 
  tap 
  connected 
  with 
  a 
  large 
  cistern 
  in 
  the 
  tower 
  of 
  

   the 
  laboratory. 
  With 
  the 
  constant 
  head 
  of 
  water 
  thus 
  pro- 
  

   vided 
  the 
  pump 
  worked 
  very 
  steadily. 
  To 
  damp 
  out 
  small 
  

   oscillations, 
  which 
  were 
  sometimes 
  produced 
  by 
  water 
  accu- 
  

   mulating 
  in 
  the 
  bends 
  of 
  the 
  composition-tube 
  joining 
  the 
  

   gauges 
  to 
  the 
  pump, 
  a 
  large 
  bottle, 
  which 
  I 
  have 
  called 
  a 
  

   " 
  collecting-bottle," 
  was 
  inserted 
  next 
  to 
  the 
  gauges. 
  All 
  three 
  

   gauges 
  connected 
  with 
  this 
  bottle, 
  as 
  did 
  also 
  an 
  extra 
  tube 
  

   which 
  served 
  as 
  a 
  by-pass. 
  Screw 
  clips 
  were 
  provided 
  to 
  all 
  

   the 
  tubes 
  communicating 
  with 
  the 
  collecting-bottle, 
  so 
  that 
  the 
  

   air-currents 
  through 
  these 
  tubes 
  could 
  be 
  readily 
  altered 
  and 
  

   adjusted. 
  

  

  (6) 
  The 
  Drying- 
  Tubes. 
  — 
  Charcoal 
  does 
  not 
  absorb 
  well 
  the 
  

   emanation 
  from 
  the 
  air 
  if 
  the 
  air 
  is 
  damp. 
  Also 
  on 
  heating 
  

   the 
  charcoal 
  any 
  water 
  given 
  off 
  condenses 
  in 
  the 
  cold 
  parts 
  

   of 
  the 
  porcelain 
  tube, 
  and 
  if 
  great 
  care 
  is 
  not 
  taken 
  the 
  tubes 
  

   crack 
  when 
  taken 
  from 
  the 
  furnace. 
  Calcium 
  chloride 
  was 
  

   used 
  as 
  a 
  dehydrating 
  agent, 
  the 
  tubes 
  used 
  being 
  about 
  

   40 
  cms. 
  long 
  and 
  1*5 
  cm. 
  in 
  diameter. 
  Eve 
  uses 
  sulphuric 
  

   acid, 
  but 
  I 
  had 
  started 
  using 
  calcium 
  chloride, 
  and 
  continued 
  

   to 
  use 
  it. 
  It 
  is 
  more 
  convenient 
  to 
  use, 
  and 
  has 
  the 
  advantage 
  

   that 
  one 
  can 
  see 
  when 
  it 
  has 
  been 
  used 
  sufficiently. 
  The 
  

   choice 
  of 
  a 
  dehydrating 
  agent 
  is, 
  however, 
  an 
  important 
  one, 
  

   as 
  besides 
  abstracting 
  the 
  water 
  it 
  might 
  abstract 
  the 
  emanation 
  

   as 
  well. 
  More 
  on 
  this 
  point 
  will 
  be 
  given 
  below. 
  

  

  Method 
  of 
  conducting 
  an 
  Experiment, 
  

   (a) 
  Measurement 
  of 
  the 
  Emanation 
  in 
  the 
  Air. 
  — 
  The 
  air 
  was 
  

   drawn 
  from 
  outside 
  by 
  a 
  glass 
  tube 
  passing 
  through 
  a 
  hole 
  in 
  

   the 
  window. 
  It 
  passed 
  in 
  succession 
  through 
  a 
  glass 
  tube 
  

   filled 
  with 
  cotton-wool 
  to 
  free 
  it 
  from 
  dust 
  (this 
  was 
  fixed 
  

   permanently 
  on 
  to 
  the 
  air-tube, 
  it 
  was 
  not 
  always 
  required 
  

   but 
  was 
  rarely 
  disconnected), 
  a 
  tube 
  filled 
  with 
  calcium 
  

  

  