﻿Constituent 
  of 
  the 
  Atmosphere. 
  289 
  

  

  In 
  this 
  formula 
  D' 
  — 
  D 
  and 
  a 
  are 
  both 
  small, 
  but 
  they 
  are 
  

   k:nown 
  with 
  fair 
  accuracy. 
  From 
  the 
  data 
  already 
  given 
  

  

  65 
  

  

  a 
  

  

  0-79X7925 
  

  

  whence 
  if 
  (on 
  an 
  arbitrary 
  scale 
  of 
  reckoning) 
  D 
  = 
  2*2990, 
  

   D' 
  •= 
  2-3102, 
  we 
  find 
  d 
  = 
  3-378. 
  Thus 
  if 
  1ST, 
  be 
  14, 
  or 
  O 
  a 
  be 
  

   16, 
  the 
  density 
  of 
  argon 
  is 
  20*6. 
  

  

  A 
  direct 
  determination 
  by^ 
  weighing 
  is 
  desirable, 
  but 
  hitherto 
  

   it 
  has 
  not 
  been 
  feasible 
  to 
  "collect 
  by 
  this 
  means 
  sufficient 
  to 
  

   fill 
  the 
  large 
  globe 
  employed 
  for 
  other 
  gases. 
  A 
  mixture 
  of 
  

   about 
  400 
  cc 
  of 
  argon 
  with 
  pure 
  oxygen, 
  however, 
  gave 
  the 
  

   weight 
  2*7315, 
  0*1045 
  in 
  excess 
  of 
  the 
  weight 
  of 
  oxygen, 
  viz: 
  

   2-6270. 
  Thus, 
  if 
  a 
  be 
  the 
  ratio 
  of 
  the 
  volume 
  of 
  argon 
  to 
  the 
  

   whole 
  volume, 
  the 
  number 
  for 
  argon 
  will 
  be 
  

  

  2-6270 
  + 
  0-1045 
  ja 
  

  

  The 
  value 
  of 
  a, 
  being 
  involved 
  only 
  in 
  the 
  excess 
  of 
  weight 
  

   above 
  that 
  of 
  oxygen, 
  does 
  not 
  require 
  to 
  be 
  known 
  very 
  accu- 
  

   rately. 
  Sufficiently 
  concordant 
  analyses 
  by 
  two 
  methods 
  gave 
  

   a 
  •= 
  0*1845 
  ; 
  whence 
  for 
  the 
  weight 
  of 
  the 
  gas 
  we 
  get 
  3*193, 
  so 
  

   that, 
  if 
  2 
  = 
  16, 
  the 
  density 
  of 
  the 
  gas 
  would 
  be 
  19*45. 
  An 
  

   allowance 
  for 
  residual 
  nitrogen, 
  still 
  visible 
  in 
  the 
  gas 
  before 
  

   admixture 
  of 
  oxygen, 
  raises 
  this 
  number 
  to 
  19*7, 
  which 
  may 
  

   be 
  taken 
  as 
  the 
  density 
  of 
  pure 
  argon 
  resulting 
  from 
  this 
  

   determination. 
  

  

  X. 
  Density 
  of 
  Argon 
  prepared 
  by 
  means 
  of 
  Magnesium. 
  

  

  The 
  density 
  of 
  the 
  original 
  sample 
  of 
  argon 
  prepared 
  has 
  

   already 
  been 
  mentioned. 
  It 
  was 
  19*09 
  ; 
  and, 
  after 
  sparking 
  

   with 
  oxygen, 
  it 
  was 
  calculated 
  to 
  be 
  20*0. 
  The 
  most 
  reliable 
  

   results 
  of 
  a 
  number 
  of 
  determinations 
  give 
  it 
  as 
  19*90. 
  The 
  

   difficulty 
  in 
  accurately 
  determining 
  the 
  density 
  is 
  to 
  make 
  sure 
  

   that 
  all 
  nitrogen 
  has 
  been 
  removed. 
  The 
  sample 
  of 
  density 
  

   19*90 
  showed 
  no 
  spectrum 
  of 
  nitrogen 
  when 
  examined 
  in 
  a 
  

   vacuum 
  tube. 
  It 
  is 
  right, 
  however, 
  to 
  remark 
  that 
  the 
  highest 
  

   density 
  registered 
  was 
  20*38. 
  But 
  there 
  is 
  some 
  reason 
  here 
  to 
  

   distrust 
  the 
  weighing 
  of 
  the 
  vacuous 
  globe. 
  

  

  XL 
  Spectrum 
  of 
  Argon. 
  

  

  The 
  spectrum 
  of 
  argon, 
  seen 
  in 
  a 
  vacuum 
  tube 
  of 
  about 
  3 
  mm 
  

   pressure, 
  consists 
  of 
  a 
  great 
  numbe 
  v 
  r 
  of 
  lines, 
  distributed 
  over 
  

   almost 
  the 
  whole 
  visible 
  field. 
  Two 
  lines 
  are 
  specially 
  charac- 
  

   teristic 
  ; 
  they 
  are 
  less 
  refrangible 
  than 
  the 
  red 
  lines 
  of 
  hydro- 
  

   gen 
  or 
  lithium, 
  and 
  serve 
  well 
  to 
  identify 
  the 
  gas, 
  when 
  

   examined 
  in 
  this 
  way. 
  Mr. 
  Crookes, 
  who 
  will 
  give 
  a 
  full 
  

  

  