﻿448 
  Dr. 
  H. 
  S. 
  Allen 
  on 
  Molecular 
  

  

  which 
  compounds 
  of 
  sodium 
  are 
  represented 
  in 
  the 
  second 
  

   list 
  by 
  the 
  corresponding 
  potassium 
  salts. 
  For 
  five 
  of 
  these 
  

   (the 
  bromide, 
  chloride, 
  fluoride, 
  iodide, 
  nitrate) 
  the 
  frequency 
  

   number 
  is 
  the 
  same 
  for 
  the 
  sodium 
  as 
  for 
  the 
  potassium 
  salt. 
  

   For 
  the 
  bromate, 
  carbonate, 
  chlorate, 
  the 
  frequency 
  number 
  

   for 
  the 
  potassium 
  compound 
  is 
  greater 
  by 
  £ 
  than 
  that 
  for 
  

   the 
  sodium 
  compound. 
  For 
  normal 
  potassium 
  sulphate 
  

   Nj/x10- 
  12 
  =9x 
  20*3, 
  as 
  compared 
  with 
  8x20*4 
  for 
  the 
  

   sodium 
  salt. 
  The 
  results 
  for 
  the 
  acid 
  sulphates 
  and 
  the 
  

   hydroxides 
  are 
  less 
  reliable. 
  

  

  The 
  bromides 
  of 
  sodium 
  and 
  potassium 
  require 
  special 
  

   consideration. 
  For 
  NaBr 
  the 
  melting-points 
  recorded 
  fall, 
  

   between 
  the 
  early 
  value 
  of 
  Oarnelley 
  (708° 
  C.) 
  and 
  that 
  

   of 
  Ruff 
  and 
  Plato 
  (765° 
  C). 
  Taking 
  the 
  latter 
  value, 
  

   Nv 
  = 
  139-7 
  x 
  10 
  12 
  . 
  For 
  KBr 
  Carnelley 
  gave 
  the 
  value 
  

   699° 
  (I, 
  whilst 
  Ruff 
  and 
  Plato 
  in 
  1903 
  found 
  750° 
  C. 
  

   Using 
  the 
  highest 
  value 
  according 
  to 
  the 
  principle 
  adopted 
  

   generally, 
  it 
  is 
  found 
  that 
  N^.139'0 
  x 
  10 
  12 
  . 
  Thus 
  if 
  the 
  

   melting-points 
  of 
  Ruff 
  and 
  Plato 
  are 
  correct, 
  the 
  values 
  of 
  

   ~Nv 
  for 
  NaBr 
  and 
  KBr 
  are 
  in 
  close 
  agreement 
  with 
  one 
  

   another; 
  but 
  they 
  cannot 
  be 
  represented 
  by 
  using 
  frequency 
  

   numbers 
  of 
  the 
  form 
  norw 
  + 
  | 
  unless 
  high 
  values 
  for 
  v 
  A 
  are 
  

   employed, 
  the 
  product 
  for 
  NaBr 
  being 
  equal 
  to 
  6^ 
  x 
  21*5 
  X 
  10 
  12 
  

   and 
  that 
  for 
  KBr 
  being 
  equal 
  to 
  6^ 
  x 
  21*4 
  x 
  10 
  12 
  . 
  A 
  redeter- 
  

   mination 
  of 
  the 
  density 
  and 
  melting-point 
  for 
  each 
  of 
  these 
  

   salts 
  is 
  to 
  be 
  desired. 
  It 
  may 
  be 
  noticed 
  that 
  both 
  LiBr 
  

   and 
  RbBr 
  give 
  normal 
  results, 
  the 
  value 
  of 
  Nv 
  for 
  the 
  

   former 
  salt 
  being 
  6 
  X 
  20*5 
  x 
  10 
  ]2 
  , 
  for 
  the 
  latter 
  7 
  x 
  205 
  x 
  10 
  12 
  ; 
  

   the 
  melting-point 
  o£ 
  CsBr 
  is 
  not 
  recorded. 
  

  

  Assuming 
  that 
  the 
  value 
  of 
  Nz> 
  X 
  10 
  ~ 
  12 
  for 
  NaBr 
  is 
  written 
  

   in 
  the 
  form 
  6^x21*5, 
  calculation 
  of 
  the 
  probability 
  by 
  the 
  

   formula 
  of 
  Laplace 
  shows 
  that 
  the 
  chance 
  of 
  an 
  accidental 
  

   concordance 
  in 
  the 
  values 
  of 
  v 
  A 
  for 
  the 
  sodium 
  salts 
  is 
  about 
  

   1 
  in 
  36. 
  

  

  The 
  agreement 
  between 
  the 
  values 
  of 
  v 
  A 
  in 
  the 
  case 
  of 
  the 
  

   compounds 
  of 
  rubidium 
  and 
  caesium 
  is 
  only 
  moderately 
  

   good. 
  Perhaps 
  it 
  may 
  be 
  safe 
  to 
  predict 
  from 
  a 
  comparison 
  

   of 
  the 
  results 
  with 
  those 
  already 
  given 
  that 
  the 
  melting- 
  

   point 
  of 
  caesium 
  iodide 
  will 
  prove 
  to 
  be 
  higher 
  than 
  the 
  

   recorded 
  value, 
  621° 
  C, 
  so 
  as 
  to 
  give 
  a 
  frequency 
  number 
  8 
  

   instead 
  of 
  7^. 
  It 
  will 
  be 
  noticed 
  that 
  in 
  general 
  the 
  

   frequency 
  numbers 
  for 
  the 
  compounds 
  of 
  the 
  alkali 
  

   metals 
  tend 
  to 
  increase 
  as 
  the 
  atomic 
  number 
  of 
  the 
  metal 
  

   increases. 
  

  

  