﻿Chemistry 
  and 
  Physics. 
  301 
  

  

  is 
  a 
  linear 
  function 
  of 
  y, 
  the 
  ratio 
  of 
  the 
  specific 
  heat 
  at 
  constant 
  

   pressure 
  to 
  that 
  at 
  constant 
  volume. 
  — 
  Proc. 
  Boy. 
  Soc, 
  95 
  A, 
  

   190, 
  1919. 
  h. 
  s. 
  u. 
  

  

  7. 
  Absorption 
  of 
  X-Bays. 
  — 
  It 
  has 
  been 
  found 
  by 
  Bragg 
  and 
  

   Pierce 
  that 
  the 
  atomic 
  absorption 
  coefficient 
  for 
  X-rays 
  is 
  equal 
  

  

  to 
  CiV 
  4 
  A? 
  , 
  where 
  N 
  == 
  atomic 
  number 
  of 
  absorber, 
  A. 
  = 
  wave- 
  

   length, 
  and 
  C 
  = 
  a 
  coefficient 
  that 
  is 
  constant 
  over 
  ranges 
  outside 
  

   the 
  region 
  of 
  selective 
  absorption. 
  ' 
  ' 
  The 
  atomic 
  absorption 
  coef- 
  

   ficient 
  expresses 
  the 
  proportion 
  of 
  the 
  energy 
  of 
  an 
  X-ray 
  pencil 
  

   which 
  is 
  absorbed 
  in 
  crossing 
  a 
  surface 
  on 
  which 
  lies 
  one 
  atom 
  

   to 
  every 
  square 
  centimetre." 
  The 
  ordinary 
  mass 
  absorption 
  

   coefficient 
  can 
  be 
  calculated 
  from 
  this 
  quantity 
  by 
  dividing 
  it 
  by 
  

   the 
  mass 
  of 
  the 
  absorbing 
  atom. 
  The 
  more 
  recent 
  work 
  of 
  Auren 
  

   on 
  a 
  fairly 
  large 
  number 
  of 
  solutions 
  led 
  to 
  the 
  conclusion 
  that 
  

   the 
  atomic 
  absorption 
  coefficient 
  is 
  not 
  proportional 
  to 
  the 
  fourth 
  

   power 
  of 
  the 
  atomic 
  number, 
  but 
  that 
  the 
  elements 
  may 
  be 
  

   divided 
  into 
  groups, 
  for 
  each 
  of 
  which 
  the 
  atomic 
  absorption 
  

   coefficient 
  is 
  directly 
  proportional 
  to 
  the 
  atomic 
  number. 
  The 
  

   cause 
  of 
  the 
  lack 
  of 
  agreement 
  between 
  the 
  results 
  just 
  stated 
  has 
  

   been 
  successfully 
  investigated 
  by 
  E. 
  A. 
  Owen. 
  

  

  This 
  experimenter 
  began 
  by 
  determining 
  the 
  values 
  of 
  p/p 
  for 
  

   filter 
  paper, 
  water, 
  magnesium, 
  aluminium, 
  nickel, 
  copper, 
  and 
  

   zinc. 
  The 
  data 
  obtained 
  showed 
  excellent 
  agreement 
  with 
  the 
  

   values 
  derived 
  from 
  the 
  work 
  of 
  Bragg 
  and 
  Pierce, 
  and 
  of 
  Hull 
  

   and 
  Rice. 
  Having 
  thus 
  obtained 
  reliable 
  mean 
  values 
  of 
  /*//> 
  

   Owen 
  brought 
  order 
  out 
  of 
  chaos 
  by 
  the 
  following 
  considerations. 
  

  

  The 
  total 
  absorption 
  coefficient 
  is 
  equal 
  to 
  the 
  sum 
  of 
  the 
  

   fluorescent 
  absorption 
  coefficient 
  and 
  the 
  scattering 
  absorption 
  

   coefficient, 
  or, 
  in 
  customary 
  notation, 
  p/p 
  = 
  r/p 
  -f- 
  a/ 
  p. 
  It 
  is 
  

   shown 
  that, 
  for 
  elements 
  having 
  atomic 
  numbers 
  less 
  than 
  (and 
  

   equal 
  to) 
  that 
  of 
  bromine, 
  the 
  scattering 
  coefficient 
  a/p 
  has 
  the 
  

   constant 
  value 
  0-2. 
  The 
  fluorescent 
  coefficient 
  r/p, 
  when 
  due 
  

   allowance 
  for 
  scattering 
  has 
  been 
  made, 
  comes 
  out 
  approximately 
  

   equal 
  to 
  C'N 
  3 
  . 
  Greater 
  accuracy 
  is 
  given 
  by 
  the 
  relation 
  that 
  the 
  

   atomic 
  fluorescent 
  absorption 
  coefficient 
  equals 
  CN*. 
  Owen 
  then 
  

   calculates 
  the 
  molecular 
  total 
  absorption 
  coefficient 
  relative 
  to 
  

   water 
  for 
  thirty-three 
  of 
  the 
  solutions 
  which 
  had 
  been 
  studied 
  by 
  

   Auren. 
  The 
  table 
  shows 
  practically 
  perfect 
  agreement 
  between 
  

   the 
  numbers 
  computed 
  by 
  Owen 
  and 
  the 
  data 
  obtained 
  experi- 
  

   mentally 
  by 
  Auren. 
  The 
  formula 
  for 
  the 
  atomic 
  fluorescent 
  

   absorption 
  coefficient 
  is 
  f 
  a 
  = 
  CiV 
  4 
  A 
  3 
  . 
  "This 
  relation 
  is 
  inde- 
  

   pendent 
  of 
  the 
  scattering 
  coefficient 
  ; 
  it 
  deals 
  only 
  with 
  the 
  loss 
  

   of 
  energy 
  of 
  X-radiation 
  by 
  the 
  production 
  of 
  corpuscular 
  radia- 
  

   tions 
  and 
  the 
  fluorescent 
  X-radiations 
  that 
  accompany 
  them." 
  

   It 
  may 
  be 
  remarked 
  incidentally 
  that 
  the 
  recalculation 
  by 
  Owen 
  

   of 
  Auren 
  's 
  data 
  involved 
  the 
  following 
  hypothesis 
  : 
  "The 
  molec- 
  

   ular 
  total 
  absorption 
  coefficient 
  of 
  a 
  complex 
  molecule 
  is 
  addi- 
  

  

  