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  V. 
  Absorption 
  of 
  Rontgen 
  Rays 
  by 
  Aqueous 
  Solutions. 
  By 
  

   R. 
  K. 
  McClung, 
  M.A., 
  Demonstrator 
  in 
  Physics, 
  and 
  

   D. 
  McIntosh, 
  M.A., 
  Demonstrator 
  in 
  Chemistry, 
  McGill 
  

   University*. 
  

  

  THE 
  question 
  of 
  the 
  absorption 
  of 
  Rontgen 
  rays 
  by- 
  

   different 
  substances 
  is 
  one 
  which 
  has 
  occupied 
  the 
  

   attention 
  of 
  various 
  investigators 
  since 
  the 
  publication 
  of 
  

   Rontgen's 
  first 
  paper. 
  The 
  permeability 
  of 
  various 
  salts, 
  

   both 
  in 
  the 
  solid 
  form 
  and 
  in 
  solution, 
  has 
  been 
  studied 
  

   to 
  some 
  extent. 
  The 
  method 
  employed 
  by 
  those 
  who 
  have 
  

   paid 
  the 
  most 
  attention 
  to 
  this 
  subject, 
  up 
  to 
  the 
  present 
  

   time, 
  has 
  been 
  a 
  photographic 
  one|. 
  This 
  consisted, 
  in 
  

   general, 
  in 
  allowing 
  the 
  Rontgen 
  rays 
  to 
  fall 
  upon 
  a 
  photo- 
  

   graphic 
  plate, 
  after 
  having 
  passed 
  through 
  the 
  substance 
  to 
  

   be 
  investigated, 
  and 
  then 
  comparing 
  the 
  impression 
  made 
  on 
  

   the 
  plate 
  when 
  different 
  substances 
  were 
  interposed 
  in 
  the 
  

   path 
  of 
  the 
  rays. 
  A 
  comparison 
  o£ 
  the 
  intensities 
  of 
  these 
  

   photographs 
  was 
  in 
  general 
  used 
  to 
  obtain 
  a 
  comparison 
  of 
  the 
  

   permeability 
  of 
  the 
  substances 
  in 
  question. 
  

  

  The 
  most 
  careful 
  investigation 
  of 
  liquids, 
  up 
  to 
  the 
  present 
  

   time, 
  by 
  this 
  photographic 
  method, 
  has 
  been 
  that 
  conducted 
  

   by 
  Lord 
  Blythswood 
  and 
  Dr. 
  Marchant 
  (Proc. 
  Roy. 
  Soc. 
  

   vol. 
  lxv. 
  1899), 
  who, 
  after 
  obtaining 
  photographs, 
  measured 
  

   the 
  intensity 
  by 
  a 
  special 
  form 
  of 
  photometer. 
  However, 
  as 
  

   we 
  believed 
  that 
  this 
  method 
  could 
  be 
  replaced 
  by 
  a 
  more 
  

   accurate 
  and 
  convenient 
  one, 
  we 
  undertook 
  to 
  investigate 
  the 
  

   question 
  by 
  an 
  electrical 
  method, 
  which 
  admits 
  of 
  more 
  rapid 
  

   measurements 
  and 
  definite 
  quantitative 
  comparisons. 
  

  

  Various 
  objections 
  may 
  be 
  raised 
  to 
  the 
  photographic 
  

   method. 
  In 
  the 
  first 
  place, 
  it 
  is 
  almost 
  impossible 
  to 
  obtain 
  

   photographic 
  plates 
  in 
  which 
  the 
  films 
  are 
  exactly 
  the 
  same 
  

   thickness 
  on 
  every 
  portion 
  of 
  the 
  plate. 
  Therefore, 
  if 
  rays 
  of 
  

   the 
  same 
  intensity 
  fall 
  upon 
  different 
  portions 
  of 
  a 
  plate, 
  

   it 
  would 
  not 
  necessarily 
  be 
  darkened 
  to 
  the 
  same 
  extent. 
  

   The 
  intensity 
  of 
  an 
  X-ray 
  photograph 
  would 
  depend 
  then 
  not 
  

   only 
  upon 
  the 
  intensity 
  of 
  the 
  rays, 
  but 
  also 
  upon 
  the 
  film. 
  

   Besides 
  this, 
  even 
  though 
  the 
  film 
  might 
  be 
  quite 
  homo- 
  

   geneous, 
  the 
  intensity 
  of 
  the 
  photograph 
  would 
  depend 
  upon 
  

  

  * 
  Communicated 
  by 
  Prof. 
  E. 
  Rutherford. 
  

  

  t 
  Bouchard, 
  Comptes 
  Rendus, 
  vol. 
  cxxiii. 
  pp. 
  967 
  & 
  1042. 
  Gladstone 
  

   & 
  Hibbert, 
  B. 
  A. 
  Reports, 
  1896, 
  1897, 
  1898. 
  Meslans, 
  Comptes 
  Rendus, 
  

   vol. 
  cxxii. 
  p. 
  307. 
  Bleunard 
  & 
  Labasse, 
  Comptes 
  Rendus, 
  vol. 
  cxxii. 
  

   pp. 
  527 
  & 
  723. 
  Novak 
  & 
  Sulc, 
  Zeit. 
  Phys. 
  Chem. 
  vol. 
  xix. 
  p. 
  489. 
  F. 
  

   Re, 
  Elettricita, 
  p. 
  261 
  (1898). 
  Van 
  Aubel, 
  Journ. 
  de 
  Physique, 
  vol. 
  v. 
  

   p. 
  511. 
  Batelli 
  & 
  Garbasso, 
  Nuov. 
  dm. 
  [4] 
  iii. 
  p. 
  40. 
  Winkelmann 
  & 
  

   Strantiel, 
  Jena. 
  Arnold, 
  Zeit. 
  fur 
  Elektrochem.\>. 
  602 
  (1896). 
  Chabaud, 
  

   Comptes 
  Rendus, 
  vol. 
  cxxii. 
  p. 
  237. 
  

  

  