﻿818 
  Prof. 
  J. 
  Clerk 
  Maxwell 
  on 
  the 
  

  

  about 
  150 
  mgr. 
  of 
  radium 
  was 
  introduced 
  and 
  left 
  for 
  three 
  

   days. 
  This 
  should 
  lead 
  to 
  the 
  production 
  of 
  about 
  j 
  1 
  ^ 
  c.mm. 
  

   of 
  helium. 
  We 
  have 
  seen 
  that 
  in 
  these 
  experiments 
  we 
  could 
  

   detect 
  with 
  certainty 
  a 
  quantity 
  of 
  neon 
  less 
  than 
  yoVo 
  c.mm. 
  

   Consequently, 
  even 
  supposing 
  that 
  the 
  emanation 
  does 
  change 
  

   into 
  neon, 
  the 
  amount 
  so 
  produced 
  cannot 
  be 
  more 
  than 
  one 
  

   per 
  cent, 
  of 
  the 
  helium 
  which 
  is 
  also 
  formed. 
  Cameron 
  and 
  

   Ramsay 
  were 
  apparently 
  not 
  aware 
  of 
  the 
  delicacy 
  of 
  the 
  

   spectroscopic 
  detection 
  of 
  neon 
  in 
  small 
  quantities 
  of 
  air. 
  

   In 
  the 
  experiment 
  described 
  in 
  their 
  last 
  paper, 
  they 
  state 
  

   that 
  they 
  were 
  unable 
  to 
  avoid 
  a 
  leakage 
  of 
  air 
  into 
  their 
  

   apparatus, 
  and 
  working 
  with 
  12*6 
  c.c. 
  of 
  mixed 
  gases, 
  they 
  

   found 
  after 
  the 
  removal 
  of 
  hydrogen 
  and 
  oxygen 
  that 
  the 
  

   residue 
  consisted 
  of 
  '292 
  c.c. 
  of 
  nitrogen 
  and 
  carbon 
  dioxide. 
  

   Assuming 
  that 
  this 
  residue 
  consisted 
  mainly 
  of 
  nitrogen, 
  it 
  

   would 
  show 
  that 
  there 
  was 
  a 
  leakage 
  of 
  air 
  of 
  about 
  '36 
  c.c. 
  

   In 
  our 
  experience, 
  the 
  admission 
  of 
  such 
  a 
  quantity 
  of 
  air 
  

   into 
  the 
  apparatus 
  gives 
  a 
  brilliant 
  spectrum 
  of 
  neon 
  com- 
  

   parable 
  in 
  brightness 
  with 
  the 
  companion 
  helium 
  spectrum. 
  

   Consequently, 
  the 
  experiment 
  described 
  by 
  Cameron 
  and 
  

   Ramsay 
  is 
  quite 
  inadequate 
  as 
  a 
  proof 
  of 
  the 
  production 
  of 
  

   neon 
  from 
  the 
  emanation. 
  

  

  University 
  of 
  Manchester, 
  

   Oct. 
  6, 
  1908. 
  

  

  LXVIII. 
  On 
  the 
  Equilibrium 
  of 
  Heterogeneous 
  Substances 
  

   (1876). 
  By 
  the 
  late 
  Prof. 
  J. 
  Clerk 
  Maxwell, 
  F.E.S. 
  

  

  [The 
  paper 
  here 
  reprinted 
  is 
  the 
  report 
  of 
  an 
  Address 
  

   delivered 
  by 
  Prof. 
  Clerk 
  Maxwell 
  on 
  May 
  24, 
  1876, 
  at 
  the 
  

   South 
  Kensington 
  Conferences 
  in 
  connexion 
  with 
  the 
  Special 
  

   Loan 
  Collection 
  of 
  Scientific 
  Apparatus. 
  It 
  is 
  contained 
  

   (pp. 
  144-150) 
  in 
  the 
  official 
  volume 
  of 
  reports 
  of 
  the 
  Con- 
  

   ferences, 
  which 
  has 
  long 
  ago 
  dropped 
  out 
  of 
  notice. 
  An 
  

   earlier 
  and 
  less 
  complete 
  version 
  of 
  this 
  summary 
  of 
  Prof. 
  

   Willard 
  Gibbs's 
  developments 
  of 
  the 
  doctrine 
  of 
  available 
  

   energy, 
  on 
  the 
  basis 
  of 
  his 
  new 
  concept 
  of 
  the 
  chemical 
  

   potentials 
  of 
  the 
  constituent 
  substances, 
  was 
  communicated 
  

   to 
  the 
  Cambridge 
  Philosophical 
  Society 
  on 
  March 
  8, 
  1876, 
  

   and 
  appeared 
  in 
  abstract 
  in 
  vol. 
  ii. 
  of 
  their 
  Proceedings, 
  

   pp. 
  427-430 
  : 
  it 
  was 
  reprinted 
  in 
  Maxwell's 
  c 
  Collected 
  

   Papers,' 
  vol. 
  ii. 
  pp. 
  498-500. 
  The 
  fact 
  that 
  the 
  energy 
  

   associated 
  with 
  any 
  constituent 
  substance 
  is 
  proportional 
  

   jointly 
  to 
  the 
  mass 
  of 
  that 
  constituent 
  and 
  to 
  another 
  factor 
  

   representing 
  energy 
  per 
  unit 
  mass, 
  is 
  of 
  course 
  involved 
  in 
  

   the 
  very 
  notion 
  of 
  conservation 
  of 
  energy 
  ; 
  but 
  the 
  general 
  

   factorization 
  into 
  magnitudes 
  (or 
  quantities) 
  and 
  intensities 
  

  

  