﻿ARTIFICIAL 
  COLD 
  WILKES 
  235 
  

  

  If 
  air 
  is 
  compressed 
  to 
  some 
  3,000 
  pounds 
  per 
  square 
  inch 
  and 
  then 
  

   allowed 
  to 
  expand 
  to 
  atmospheric 
  pressure, 
  it 
  is 
  cooled 
  approximately 
  

   50° 
  F. 
  With 
  the 
  aid 
  of 
  a 
  regenerative 
  coil, 
  this 
  cooled, 
  expanded 
  air 
  can 
  

   be 
  forced 
  into 
  close 
  contact 
  with 
  the 
  high-pressure 
  air, 
  thus 
  cooling 
  the 
  

   high-pressure 
  air. 
  If 
  this 
  process 
  is 
  continued, 
  a 
  point 
  will 
  soon 
  be 
  

   reached 
  where 
  the 
  cooling 
  effect 
  will 
  cause 
  some 
  of 
  the 
  escaping 
  air 
  to 
  

   be 
  cooled 
  to 
  the 
  liquefaction 
  temperature 
  and 
  liquid 
  air 
  can 
  be 
  col- 
  

   lected 
  at 
  the 
  bottom 
  of 
  the 
  expansion 
  coil. 
  For 
  some 
  time 
  after 
  the 
  

   discovery 
  of 
  the 
  method 
  of 
  producing 
  liquid 
  air, 
  the 
  material 
  was 
  

   largely 
  for 
  laboratory 
  use 
  only, 
  but 
  now 
  the 
  commercial 
  use 
  has 
  

   increased 
  to 
  such 
  an 
  extent 
  that 
  there 
  is 
  scarcely 
  a 
  large-sized 
  city 
  

   that 
  does 
  not 
  have 
  at 
  least 
  one 
  liquid-air 
  plant 
  in 
  operation. 
  In 
  the 
  

   modern 
  plants, 
  the 
  expanding 
  air 
  operates 
  a 
  compressor, 
  thus 
  increas- 
  

   ing 
  the 
  efficiency 
  over 
  the 
  earlier 
  laboratory 
  methods. 
  

  

  Air 
  contains 
  roughly 
  20 
  per 
  cent 
  oxj^gen 
  and 
  80 
  per 
  cent 
  nitrogen, 
  

   but 
  the 
  boiling 
  point 
  of 
  nitrogen 
  is 
  320° 
  F. 
  below 
  zero 
  while 
  oxygen 
  

   boils 
  at 
  only 
  297° 
  F. 
  below 
  zero. 
  Due 
  to 
  this 
  difference 
  in 
  boiling 
  

   temperatures 
  the 
  nitrogen 
  tends 
  to 
  vaporize 
  first 
  and 
  it 
  is 
  possible 
  to 
  

   separate 
  these 
  two 
  substances 
  by 
  fractional 
  distillation 
  in 
  much 
  the 
  

   same 
  way 
  as 
  gasoline 
  is 
  separated 
  from 
  crude 
  oil, 
  but 
  no 
  external 
  

   heat 
  is 
  required 
  to 
  boil 
  liquid 
  air 
  because 
  the 
  normal 
  boiling 
  point 
  is 
  

   about 
  310° 
  F. 
  below 
  zero. 
  

  

  Liquid 
  air 
  is 
  also 
  used 
  in 
  high-vacuum 
  work 
  and 
  is 
  used 
  for 
  the 
  

   production 
  of 
  helium 
  from 
  natural 
  gas 
  in 
  Texas. 
  A 
  prominent 
  mining 
  

   engineer 
  states 
  that 
  90 
  per 
  cent 
  of 
  the 
  explosive 
  work 
  in 
  the 
  mines 
  in 
  

   Mexico 
  is 
  carried 
  out 
  with 
  liquid 
  oxygen 
  as 
  the 
  explosive 
  rather 
  than 
  

   gun 
  powder. 
  If 
  blotting 
  paper 
  is 
  rolled 
  up 
  and 
  saturated 
  with 
  liquid 
  

   oxygen 
  and 
  then 
  tamped 
  into 
  a 
  drilled 
  hole, 
  it 
  can 
  be 
  ignited 
  electri- 
  

   cally 
  and 
  an 
  explosion 
  similar 
  to 
  that 
  of 
  gunpowder 
  will 
  result. 
  

  

  