﻿330 
  Scientific 
  Intelligence. 
  

  

  Anderson 
  and 
  R. 
  J. 
  Nestell 
  have 
  made 
  a 
  long 
  series 
  of 
  ex- 
  

   periments 
  with 
  a 
  number 
  of 
  actual 
  cement 
  materials. 
  They 
  have 
  

   found 
  that 
  it 
  is 
  possible 
  to 
  volatilize 
  all 
  the 
  potash 
  from 
  cement 
  

   material 
  provided 
  the 
  temperature, 
  time, 
  and 
  volume 
  of 
  gases 
  are 
  

   sufficient. 
  The 
  lower 
  point 
  of 
  temperature 
  for 
  this 
  volatilization 
  

   is 
  1100° 
  C, 
  and 
  the 
  rate 
  increases 
  rapidly 
  with 
  the 
  temperature. 
  

   The 
  presence 
  of 
  chlorides, 
  particularly 
  calcium 
  chloride, 
  increases 
  

   the 
  rapidity, 
  while 
  sulphates 
  decrease 
  it. 
  Sodium 
  is 
  driven 
  off 
  

   nearly 
  as 
  easily 
  as 
  the 
  potassium. 
  No 
  conclusions 
  are 
  given 
  as 
  

   to 
  the 
  applicability 
  of 
  this 
  operation 
  as 
  a 
  practical 
  source 
  of 
  

   potassium 
  salts. 
  — 
  Jour. 
  Indust. 
  and 
  Eng. 
  Chem., 
  ix, 
  253. 
  

  

  H. 
  L. 
  W. 
  

  

  6. 
  Dispersion 
  and 
  the 
  Size 
  of 
  Molecules 
  of 
  Hydrogen, 
  

   Oxygen, 
  and 
  Nitrogen. 
  — 
  From 
  theoretical 
  considerations, 
  it 
  has 
  

   been 
  recently 
  shown 
  by 
  L. 
  Silberstein 
  that 
  the 
  molecular 
  refrac- 
  

   tivity 
  N 
  of 
  an 
  isotropic 
  substance 
  the 
  molecules 
  of 
  which 
  

   consist 
  of 
  two 
  equal 
  atoms 
  may 
  be 
  expressed 
  by 
  the 
  formula 
  

   N— 
  (2/3) 
  JV 
  [2 
  + 
  (1 
  — 
  o-iVo)- 
  1 
  ]. 
  JV 
  denotes 
  the 
  atomic 
  refrac- 
  

   tivity, 
  and 
  a 
  = 
  a/ 
  (2ttR 
  3 
  ) 
  ; 
  where 
  a 
  = 
  3m 
  H 
  /l*008 
  — 
  4-88 
  X 
  10™ 
  24 
  

   gram, 
  and 
  R 
  symbolizes 
  the 
  mutual 
  distance 
  of 
  the 
  " 
  centers 
  " 
  of 
  

   the 
  two 
  atoms 
  composing 
  each 
  molecule, 
  that 
  is, 
  of 
  the 
  positions 
  

   of 
  equilibrium 
  of 
  the 
  dispersive 
  particles 
  within 
  their 
  atoms. 
  

   This 
  formula 
  reduces 
  to 
  the 
  usual 
  relation 
  JSf 
  = 
  2JV 
  Q 
  when 
  R 
  is 
  so 
  

   large 
  as 
  to 
  make 
  <tN 
  negligible 
  as 
  compared 
  with 
  unity, 
  and 
  

   it 
  owes 
  its 
  generality 
  to 
  the 
  fact 
  that 
  in 
  its 
  derivation 
  the 
  

   mutual 
  influence 
  of 
  the 
  atoms 
  in 
  one 
  molecule 
  was 
  taken 
  into 
  

   account. 
  When 
  XjX 
  is 
  small 
  enough 
  to 
  admit 
  of 
  the 
  omission 
  

   of 
  terms 
  involving 
  the 
  fourth 
  and 
  higher 
  powers 
  of 
  this 
  ratio 
  the 
  

   equations 
  of 
  refractivity 
  reduce 
  to 
  the 
  very 
  simple 
  form 
  

   N~= 
  b 
  + 
  g/M* 
  and 
  JV 
  = 
  b 
  + 
  <7o/A. 
  2 
  - 
  A. 
  and 
  X 
  denote 
  respectively 
  

   the 
  wave-length 
  of 
  an 
  incident 
  radiation 
  in 
  the 
  visible 
  spectrum 
  

   and 
  the 
  free 
  wave-length 
  in 
  the 
  extreme 
  ultra-violet 
  characteristic 
  

   of 
  each 
  atom 
  when 
  undisturbed 
  by 
  its 
  neighbors. 
  b 
  and 
  g 
  are 
  

   explicit 
  functions 
  of 
  certain 
  properties 
  of 
  the 
  atoms, 
  such 
  as 
  

   A 
  , 
  a-, 
  the 
  mass 
  m 
  of 
  a 
  dispersive 
  particle, 
  and 
  the 
  charge 
  e 
  of 
  such 
  

   a 
  particle, 
  b 
  and 
  g, 
  which 
  are 
  called 
  respectively 
  the 
  " 
  refraction- 
  

   coefficient" 
  and 
  the 
  "dispersion-coefficient," 
  are 
  amenable 
  to 
  

   direct 
  experimental 
  determination. 
  Under 
  the 
  conditions 
  of 
  ap- 
  

   proximation 
  considered, 
  b 
  and 
  g 
  are 
  dependent 
  upon 
  b 
  0t 
  g 
  Q 
  and 
  R 
  

   (through 
  o-) 
  in 
  the 
  following 
  manner: 
  b 
  = 
  (2/3) 
  b 
  [2 
  + 
  (1 
  — 
  oA) 
  _1 
  ] 
  

   and 
  g 
  = 
  (2/3) 
  <7 
  [2 
  4- 
  (1 
  — 
  o-& 
  ) 
  -2 
  ]. 
  The 
  denominator 
  1 
  — 
  a-b 
  

   being 
  a 
  fraction, 
  the 
  dispersion 
  will 
  show 
  a 
  greater 
  departure 
  

   from 
  additivity 
  than 
  the 
  refraction, 
  which 
  is 
  a 
  well-known 
  feature 
  

   of 
  this 
  class 
  of 
  phenomena. 
  

  

  The 
  problem 
  before 
  us 
  may 
  now 
  be 
  stated: 
  " 
  Given 
  the 
  molec- 
  

   ular 
  refractivity 
  JV 
  of 
  the 
  diatomic 
  substance, 
  that 
  is, 
  given 
  its 
  

   coefficients 
  b, 
  g, 
  find 
  the 
  atomic 
  coefficients 
  b 
  Ql 
  g 
  , 
  and 
  therefore 
  

   the 
  atomic 
  refractivity 
  iVo, 
  and 
  also 
  the 
  interatomic 
  distance 
  R 
  

   involved 
  in 
  <r." 
  Obviously, 
  another 
  relation 
  between 
  b 
  and 
  g 
  is 
  

   necessary 
  for 
  the 
  solution 
  of 
  the 
  last 
  two 
  equations. 
  Silberstein 
  

  

  