﻿Variation 
  of 
  Manganin 
  Resistances 
  uith 
  Humidity. 
  451 
  

  

  After 
  the 
  10,000 
  ohm 
  coil 
  had 
  been 
  in 
  the 
  box 
  for 
  8 
  days 
  

   in 
  an 
  atmosphere 
  dried 
  with 
  fused 
  calcium 
  chloride, 
  its 
  re- 
  

   sistance 
  was 
  identical 
  with 
  its 
  value 
  in 
  an 
  atmosphere 
  of 
  

   60 
  per 
  cent, 
  relative 
  humidity. 
  When 
  water 
  was 
  substituted 
  

   for 
  the 
  calcium 
  chloride 
  and 
  20 
  days 
  had 
  elapsed, 
  the 
  re- 
  

   sistance 
  of 
  the 
  coil 
  was 
  7 
  parts 
  in 
  100,000 
  lower 
  than 
  before; 
  

   but 
  on 
  opening 
  the 
  box 
  and 
  exposing 
  the 
  coil 
  to 
  the 
  outer 
  

   atmosphere, 
  the 
  resistance 
  rose 
  to 
  to 
  its 
  normal 
  value 
  within 
  

   20 
  minutes. 
  We 
  concluded, 
  therefore, 
  that 
  the 
  low 
  value 
  

   was 
  a 
  result 
  of 
  leakage, 
  and 
  we 
  suspected 
  the 
  presence 
  of 
  a 
  

   thin 
  film 
  of 
  moisture 
  on 
  the 
  ebonite. 
  In 
  some 
  later 
  experi- 
  

   ments 
  such 
  a 
  film 
  was 
  visible, 
  and 
  the 
  main 
  leakage 
  was 
  

   undoubtedly 
  that 
  between 
  the 
  current 
  leads 
  of 
  the 
  coil 
  and 
  

   the 
  metal 
  cylinder 
  on 
  which 
  the 
  coil 
  is 
  wound. 
  The 
  gap 
  

   between 
  the 
  leads 
  and 
  the 
  cylinder 
  is 
  about 
  5 
  mm. 
  In 
  the 
  

   experiments 
  cited 
  above 
  the 
  temperature 
  of 
  the 
  box 
  and 
  its 
  

   contents 
  was 
  raised 
  to 
  35° 
  C, 
  but 
  as 
  this 
  appeared 
  to 
  be 
  a 
  

   doubtful 
  procedure, 
  all 
  subsequent 
  experiments 
  with 
  coils 
  in 
  

   saturated 
  atmospheres 
  were 
  made 
  at 
  the 
  temperature 
  of 
  the 
  air. 
  

  

  We 
  next 
  placed 
  the 
  10,000 
  ohm 
  coil 
  in 
  an 
  atmosphere 
  

   dried 
  with 
  phosphoric 
  anhydride, 
  and 
  after 
  the 
  expiration 
  of 
  

   30 
  days 
  its 
  resistance 
  was 
  again 
  measured. 
  It 
  was 
  2 
  parts 
  

   in 
  100,000 
  lower 
  than 
  normal. 
  Afterwards, 
  acting 
  on 
  a 
  

   suggestion 
  from 
  Dr. 
  Rosa, 
  the 
  coil 
  was 
  sealed 
  inside 
  a 
  glass 
  

   beaker, 
  at 
  the 
  base 
  of 
  which 
  either 
  fused 
  calcium 
  chloride, 
  

   or 
  phosphoric 
  anhydride, 
  or 
  water 
  could 
  be 
  placed. 
  Before 
  

   sealing 
  (when 
  a 
  dry 
  atmosphere 
  was 
  desired) 
  the 
  beaker 
  and 
  

   its 
  contents 
  were 
  placed 
  for 
  8 
  hours 
  in 
  an 
  atmosphere 
  at 
  low 
  

   pressure 
  — 
  the 
  pressure 
  recorded 
  being 
  3 
  cms. 
  of 
  mercury. 
  

   After 
  the 
  coil 
  had 
  been 
  exposed 
  for 
  4 
  days 
  to 
  the 
  action 
  of 
  

   an 
  atmosphere 
  dried 
  with 
  phosphoric 
  anhydride, 
  the 
  resistance 
  

   was 
  1 
  part 
  in 
  100,000 
  lower 
  than 
  normal, 
  and 
  after 
  being 
  

   exposed 
  for 
  4 
  days 
  in 
  an 
  atmosphere 
  approximately 
  saturated 
  

   with 
  water, 
  the 
  resistance 
  was 
  11 
  parts 
  in 
  100,000 
  low. 
  The 
  

   latter 
  effect 
  was 
  again 
  found 
  to 
  be 
  due 
  to 
  leakage, 
  for 
  on 
  

   exposing 
  the 
  coil 
  to 
  the 
  air 
  of 
  the 
  room 
  the 
  resistance 
  between 
  

   the 
  current 
  leads 
  rose 
  in 
  the 
  following 
  manner 
  : 
  — 
  

  

  Before 
  exposure 
  to 
  air 
  of 
  room, 
  resistance 
  low 
  by 
  O'Oll 
  p. 
  cent. 
  

  

  After 
  

  

  3 
  minutes 
  „ 
  , 
  

  

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