﻿Chemistry 
  and 
  Physics. 
  57 
  

  

  N 
  2 
  2 
  and 
  N 
  4 
  show 
  scarcely 
  any 
  tendency 
  to 
  unite 
  at 
  the 
  ordi- 
  

   nary 
  temperature, 
  the 
  authors 
  find 
  that 
  at 
  —21°, 
  these 
  oxides 
  

   combine 
  in 
  exact 
  molecular 
  proportions 
  to 
  form 
  N 
  2 
  3 
  which 
  con- 
  

   denses 
  as 
  an 
  indigo-blue 
  liquid 
  ; 
  98*3 
  per 
  cent 
  of 
  the 
  trioxide 
  

   having 
  been 
  obtained 
  in 
  one 
  experiment. 
  It 
  is 
  perfectly 
  stable 
  

   at 
  and 
  below 
  this 
  temperature 
  ; 
  but 
  at 
  a 
  slightly 
  higher 
  tempera- 
  

   ture, 
  even 
  under 
  pressure, 
  it 
  begins 
  to 
  decompose, 
  the 
  dissocia- 
  

   tion 
  becoming 
  almost 
  complete 
  on 
  conversion 
  of 
  the 
  liquid 
  into 
  

   gas. 
  Hence 
  it 
  would 
  seem 
  that 
  the 
  trioxide 
  is 
  not 
  capable 
  of 
  ex- 
  

   isting 
  in 
  the 
  gaseous 
  state 
  ; 
  although 
  certain 
  facts 
  observed 
  in 
  

   the 
  investigation 
  seem 
  to 
  indicate 
  that 
  a 
  residue 
  of 
  N 
  2 
  3 
  mole- 
  

   cules 
  may 
  escape 
  dissociation 
  and 
  may 
  exist 
  side 
  by 
  side 
  with 
  the 
  

   molecules 
  of 
  N 
  2 
  2 
  and 
  N 
  2 
  4 
  into 
  which 
  the 
  trioxide 
  is 
  decom- 
  

   posed. 
  — 
  Zeitschr. 
  anorg. 
  Chem., 
  vii, 
  209, 
  September, 
  1894. 
  

  

  G. 
  P. 
  B. 
  

  

  3. 
  On 
  the 
  Physical 
  Properties 
  of 
  Nitrogen 
  3Ionoxide. 
  — 
  The 
  

   physical 
  properties 
  of 
  carelully 
  purified 
  nitrogen 
  monoxide 
  have 
  

   been 
  studied 
  by 
  Villard. 
  The 
  gas 
  was 
  obtained 
  pure 
  either 
  by 
  

   the 
  decomposition 
  of 
  its 
  hydrate 
  or 
  by 
  fractioning 
  the 
  liquid 
  

   oxide; 
  the 
  gas 
  in 
  the 
  latter 
  case 
  being 
  passed 
  through 
  suitable 
  

   purifying 
  and 
  drying 
  agents. 
  It 
  was 
  then 
  liquefied 
  and 
  allowed 
  to 
  

   boil 
  to 
  expel 
  the 
  dissolved 
  gases. 
  As 
  thus 
  obtained, 
  it 
  is 
  free 
  

   from 
  the 
  less 
  liquefiable 
  gases, 
  its 
  maximum 
  vapor 
  pressure 
  is 
  in- 
  

   dependent 
  of 
  the 
  volume 
  of 
  the 
  vapor, 
  and 
  a 
  small 
  increase 
  of 
  

   pressure 
  causes 
  complete 
  liquefaction. 
  The 
  densities 
  of 
  the 
  gas 
  

   and 
  of 
  the 
  liquid 
  at 
  various 
  temperatures 
  are 
  given 
  as 
  follows 
  : 
  

  

  Temperature 
  0° 
  5° 
  10° 
  17-5° 
  26-5° 
  32*9° 
  34-9° 
  36*3° 
  

  

  Density 
  of 
  liquid.. 
  0-9105 
  885 
  0*856 
  0-804 
  0-720 
  0-640 
  0*605 
  0-572 
  

   Density 
  of 
  gas 
  0-0870 
  099 
  0*114 
  0-146 
  0*207 
  0'275 
  0-305 
  0*338 
  

  

  The 
  critical 
  temperature 
  of 
  pure 
  N 
  2 
  is 
  38*8°, 
  the 
  critical 
  volume 
  

   is 
  0*00436, 
  the 
  critical 
  density 
  0*454 
  and 
  the 
  critical 
  pressure 
  77 
  - 
  5 
  

   atmospheres. 
  — 
  C. 
  P., 
  cxviii, 
  1096, 
  May, 
  1894. 
  g. 
  f. 
  b. 
  

  

  4. 
  On 
  the 
  use 
  of 
  the 
  Refractive 
  Pidex 
  for 
  determining 
  Criti- 
  

   cal 
  Temperatures. 
  — 
  By 
  a 
  careful 
  observation 
  of 
  the 
  interference 
  

   bands, 
  Chappuis 
  has 
  been 
  able 
  to 
  note 
  the 
  changes 
  which 
  take 
  

   place 
  in 
  the 
  index 
  of 
  refraction 
  of 
  a 
  liquefied 
  gas 
  in 
  the 
  vicinity 
  

   of 
  its 
  critical 
  temperature. 
  For 
  this 
  purpose 
  the 
  liquid 
  was 
  con- 
  

   tained 
  in 
  a 
  cylindrical 
  cavity 
  in 
  a 
  steel 
  prism, 
  having 
  apertures 
  

   closed 
  by 
  optically 
  plane 
  and 
  parallel 
  glass 
  plates 
  ; 
  the 
  whole 
  

   being 
  immersed 
  in 
  a 
  liquid 
  whose 
  temperature 
  could 
  be 
  main- 
  

   tained 
  constant. 
  By 
  means 
  of 
  a 
  pair 
  of 
  Jamin 
  mirrors, 
  two 
  

   beams 
  of 
  light, 
  starting 
  from 
  a 
  Billet 
  compensator, 
  pass 
  through 
  

   the 
  liquid 
  in 
  the 
  prism, 
  traversing 
  in 
  their 
  course 
  the 
  enveloping 
  

   bath, 
  the 
  sides 
  of 
  which 
  also 
  are 
  made 
  of 
  plane 
  parallel 
  glass. 
  

   When 
  liquid 
  carbon 
  dioxide 
  is 
  used, 
  the 
  refractive 
  index 
  is 
  con- 
  

   stant 
  and 
  the 
  bands 
  remain 
  stationary 
  ; 
  beyond 
  this 
  temperature 
  

   the 
  refractive 
  index 
  increases 
  rapidly 
  and 
  the 
  bands.fall. 
  At 
  

   31-61° 
  the 
  curve 
  of 
  the 
  index 
  shows 
  a 
  vertical 
  tangent; 
  and 
  the 
  

   intersection 
  of 
  this 
  curve 
  with 
  the 
  straight 
  line 
  which 
  represents 
  

   the 
  index 
  above 
  this 
  temperature, 
  is 
  the 
  critical 
  point 
  of 
  the 
  

  

  