﻿frequency 
  and 
  Molecular 
  Number. 
  

  

  345 
  

  

  One 
  point 
  of 
  interest 
  may 
  be 
  mentioned. 
  Inorganic 
  com- 
  

   pounds 
  which 
  contain 
  water 
  of 
  crystallization 
  conform 
  to 
  the 
  

   general 
  rule. 
  In 
  some 
  cases 
  the 
  frequency 
  number 
  of 
  the 
  

   dehydrated 
  salt 
  is 
  the 
  same 
  as 
  that 
  of 
  the 
  hydrated 
  compound. 
  

   Thus 
  for 
  sodium 
  sulphate 
  (Na 
  2 
  S0 
  4 
  ) 
  the 
  value 
  of 
  Nj> 
  is 
  

   8x20-4 
  x 
  10 
  12 
  , 
  for 
  the 
  hydrated 
  salt 
  (Na 
  2 
  S0 
  4 
  . 
  10H 
  2 
  O) 
  it 
  is 
  

   8x20*6xl0 
  12 
  . 
  In 
  other 
  cases 
  there 
  is 
  a 
  change 
  in 
  the 
  

   frequency 
  number. 
  An 
  example 
  is 
  afforded 
  by 
  calcium 
  

   nitrate 
  — 
  the 
  anhydrous 
  salt 
  (Ca(N0 
  3 
  ) 
  2 
  ) 
  gives 
  for 
  the 
  product 
  

   Nz/ 
  the 
  value 
  6^-x 
  21*3 
  x 
  10 
  12 
  , 
  whilst 
  the 
  hydrated 
  compound 
  

   (Ca(NO 
  s 
  ) 
  2 
  . 
  4^0) 
  gives 
  4 
  x 
  21*5 
  x 
  10 
  12 
  . 
  

  

  A 
  comparison 
  between 
  the 
  results 
  obtained 
  from 
  the 
  specific 
  

   heat 
  at 
  low 
  temperatures 
  and 
  those 
  found 
  by 
  calculation 
  from 
  

   Lindemann/s 
  formula 
  is 
  only 
  possible 
  in 
  a 
  few 
  cases. 
  

  

  Table 
  III. 
  

  

  Compound. 
  

  

  XvXlO- 
  12 
  . 
  

  

  NaCl 
  

  

  KC1 
  

  

  AgCl 
  

  

  CaF, 
  

  

  Specific 
  heat. 
  Lindemann's 
  formula. 
  

  

  8 
  X 
  21-01 
  

   61x20-6/ 
  

   8 
  X 
  20-51 
  

   6 
  X20-8J 
  

   6|X21() 
  

   18 
  X20-9 
  

  

  6x20-5 
  

  

  6x20-9 
  

  

  7X21-4 
  

  

  fly'Oi 
  

  

  FeS," 
  

  

  36 
  X21-8 
  10x21-7 
  

  

  

  

  

  It 
  is 
  curious 
  that 
  there 
  should 
  be 
  such 
  a 
  large 
  difference 
  

   between 
  the 
  two 
  values 
  of 
  the 
  frequency 
  numbers 
  for 
  calcium 
  

   fluoride 
  and 
  iron 
  disulphide. 
  Interpreted 
  according 
  to 
  the 
  

   theory 
  of 
  Nernst, 
  this 
  may 
  indicate 
  that 
  for 
  these 
  compounds 
  

   the 
  contribution 
  to 
  the 
  specific 
  heat 
  arising 
  from 
  the 
  internal 
  

   vibrations 
  of 
  the 
  molecule 
  forms 
  an 
  important 
  part 
  of 
  the 
  

   whole. 
  

  

  § 
  6. 
  Organic 
  Compounds 
  (Lindemann's 
  Formula). 
  

  

  Chemists 
  have 
  not, 
  as 
  a 
  rule, 
  devoted 
  great 
  attention 
  to 
  

   the 
  determination 
  of 
  the 
  density 
  of 
  organic 
  compounds 
  in 
  the 
  

   solid 
  state. 
  On 
  examining 
  such 
  a 
  Table 
  as 
  that 
  given 
  in 
  

   the 
  ' 
  Chemical 
  Annual 
  ' 
  it 
  will 
  be 
  found 
  in 
  general 
  that 
  where 
  

   the 
  density 
  of 
  the 
  solid 
  is 
  recorded, 
  the 
  melting-point 
  is 
  

   wanting 
  and 
  vice 
  versa. 
  Amongst 
  the 
  results 
  available 
  up 
  

   to 
  the 
  present 
  time 
  are 
  to 
  be 
  found 
  many 
  suggestive 
  cross- 
  

   relationships 
  between 
  the 
  values 
  of 
  Ni^xlO 
  -12 
  , 
  in 
  which 
  

   a 
  number 
  approximating 
  to 
  21 
  or 
  | 
  x 
  21 
  is 
  of 
  frequent 
  

   occurrence. 
  This 
  is 
  illustrated 
  for 
  some 
  aliphatic 
  derivatives 
  

   in 
  the 
  following 
  Table. 
  

  

  