﻿Duane 
  and 
  Lory 
  — 
  Electrical 
  Thermostat. 
  179 
  

  

  Art. 
  XVII. 
  — 
  An 
  Electrical 
  Thermostat; 
  by 
  William 
  

   Duane 
  and 
  Charles 
  A. 
  Lory. 
  

  

  In 
  some 
  research 
  work 
  that 
  one 
  of 
  us 
  has 
  been 
  carrying 
  on 
  

   recently, 
  it 
  became 
  necessary 
  to 
  construct 
  an 
  easily 
  adjustable 
  

   thermostat 
  that 
  would 
  keep 
  the 
  temperature 
  of 
  a 
  bath 
  constant 
  

   to 
  within 
  y^g-th 
  of 
  a 
  degree 
  Centigrade 
  for 
  a 
  considerable 
  

   length 
  of 
  time. 
  It 
  was 
  thought 
  that 
  this 
  could 
  be 
  accom- 
  

   plished 
  best 
  by 
  means 
  of 
  an 
  electric 
  current, 
  because 
  if 
  the 
  

   current 
  passed 
  through 
  wires 
  suspended 
  in 
  the 
  bath, 
  or 
  through 
  

   a 
  conducting 
  bath 
  itself, 
  heat 
  would 
  be 
  supplied 
  throughout 
  

   the 
  whole 
  bath 
  much 
  more 
  easily 
  and 
  quickly 
  than 
  by 
  other 
  

   means. 
  

  

  The 
  result 
  of 
  our 
  endeavor 
  to 
  construct 
  such 
  an 
  electrical 
  

   thermostat 
  has 
  been 
  quite 
  satisfactory. 
  Daring 
  the 
  trial 
  runs 
  

   the 
  temperature 
  of 
  the 
  thermostat 
  remained 
  constant 
  to 
  within 
  

   less 
  than 
  goVo^ 
  1 
  °^ 
  a 
  degree 
  Centigrade, 
  although 
  several 
  times 
  

   the 
  temperature 
  of 
  the 
  surrounding 
  atmosphere 
  varied 
  12° 
  C. 
  

   or 
  15° 
  C. 
  in 
  half 
  an 
  hour. 
  

  

  The 
  general 
  scheme 
  is 
  this. 
  Through 
  a 
  conducting 
  liquid, 
  or 
  

   through 
  wires 
  immersed 
  in 
  one 
  which 
  is 
  non-conducting, 
  

   flows 
  an 
  electric 
  current, 
  that 
  is 
  sufficiently 
  large 
  to 
  heat 
  the 
  

   liquid 
  up 
  to 
  a 
  temperature 
  considerably 
  above 
  the 
  constant 
  

   temperature 
  required. 
  A 
  system 
  of 
  tubes 
  containing 
  a 
  liquid 
  

   with 
  a 
  large 
  temperature-coefficient 
  of 
  expansion 
  is 
  placed 
  in 
  

   the 
  bath. 
  By 
  means 
  of 
  a 
  suitable 
  mechanism 
  the 
  expansion 
  of 
  

   this 
  liquid 
  interrupts 
  or 
  reduces 
  the 
  strength 
  of 
  the 
  heating 
  

   current 
  when 
  the 
  required 
  temperature 
  has 
  been 
  reached. 
  The 
  

   temperature 
  of 
  the 
  bath 
  then 
  begins 
  to 
  fall, 
  whereupon 
  the 
  

   original 
  current 
  is 
  started 
  again 
  automatically. 
  It 
  might 
  seem 
  

   at 
  first 
  thought, 
  that, 
  owing 
  to 
  the 
  time 
  required 
  for 
  the 
  heat 
  

   to 
  penetrate 
  through 
  the 
  walls 
  of 
  the 
  tubes 
  to 
  the 
  expanding 
  

   liquid 
  within, 
  the 
  making 
  and 
  breaking 
  of 
  the 
  circuit 
  would 
  

   take 
  place 
  rather 
  slowly, 
  and 
  the 
  temperature 
  of 
  the 
  bath 
  

   would 
  be 
  oscillatory 
  instead 
  of 
  constant. 
  This 
  is 
  undoubtedly 
  

   true 
  to 
  a 
  certain 
  extent. 
  Practically, 
  however, 
  with 
  our 
  

   arrangement 
  of 
  apparatus 
  the 
  variation 
  of 
  temperature 
  is 
  too 
  

   small 
  to 
  be 
  detected 
  even 
  by 
  a 
  differential 
  thermometer 
  that 
  

   would 
  indicate 
  a 
  change 
  of 
  temperature 
  of 
  ^^th 
  of 
  a 
  degree 
  

   Centigrade. 
  Indeed 
  the 
  efficiency 
  of 
  the 
  apparatus 
  is 
  due 
  to 
  

   the 
  fact 
  that 
  the 
  makes 
  and 
  breaks 
  follow 
  each 
  other 
  so 
  rapidly, 
  

   that 
  there 
  is 
  not 
  time 
  for 
  the 
  temperature 
  to 
  change 
  percep- 
  

   tibly 
  between 
  them. 
  Often 
  two, 
  three 
  or 
  even 
  more 
  interrup- 
  

   tions 
  of 
  the 
  current 
  occur 
  in 
  one 
  second. 
  At 
  first 
  we 
  used 
  an 
  

   ordinary 
  wash-boiler 
  containing 
  about 
  150 
  liters 
  of 
  water 
  as 
  a 
  

  

  