﻿52 
  Dr. 
  A. 
  C. 
  Crehore 
  on 
  the 
  Formation 
  of 
  tlie 
  

  

  calculated, 
  and 
  illustrates 
  the 
  case. 
  The 
  distance 
  between 
  

   the 
  carbon 
  and 
  hydrogen 
  atoms 
  is 
  /3v 
  = 
  13*75, 
  and 
  between 
  

   diametrically 
  opposite 
  hydrogen 
  atoms, 
  /3v= 
  15*08. 
  If 
  

   nitrogen 
  were 
  substituted 
  for 
  the 
  carbon 
  with 
  the 
  four 
  

   hydrogen 
  atoms, 
  the 
  distances 
  would 
  be 
  greater 
  yet 
  ; 
  and 
  if 
  

   oxygen 
  or 
  fluorine 
  were 
  substituted 
  for 
  the 
  carbon, 
  the 
  

   distances 
  rapidly 
  increase 
  for 
  each 
  change. 
  This 
  is 
  due 
  to 
  

   the 
  differences 
  in 
  these 
  atoms 
  which 
  make 
  the 
  small 
  

   differences 
  in 
  the 
  angles 
  of 
  the 
  diatomic 
  molecules 
  shown 
  in 
  

   the 
  figures. 
  Consequently 
  the 
  degree 
  of 
  stability 
  is 
  greater 
  

   with 
  carbon 
  combined 
  with 
  four 
  hydrogen 
  atoms 
  in 
  a 
  ring 
  

   than 
  it 
  is 
  with 
  nitrogen 
  so 
  combined, 
  and 
  with 
  nitrogen 
  

   than 
  with 
  oxygen, 
  and 
  with 
  oxygen 
  than 
  with 
  fluorine. 
  

  

  The 
  dimensions 
  of 
  this 
  molecule 
  from 
  atom 
  to 
  atom 
  seem 
  

   to 
  be 
  too 
  great 
  for 
  long 
  continued 
  existence 
  as 
  a 
  compound 
  

   molecule 
  ; 
  but 
  if 
  two 
  of 
  the 
  hydrogen 
  atoms 
  are 
  removed 
  

   from 
  the 
  upper 
  and 
  placed 
  in 
  the 
  lower 
  ring 
  of 
  the 
  carbon 
  

   atom, 
  it 
  is 
  found 
  that 
  the 
  distance 
  between 
  the 
  carbon 
  and 
  

   hydrogen 
  atoms 
  is 
  reduced 
  from 
  13*75 
  to 
  6*85, 
  which 
  is 
  

   almost 
  exactly 
  one-half 
  of 
  the 
  former 
  distance. 
  The 
  distance 
  

   between 
  the 
  hydrogen 
  atoms 
  in 
  the 
  same 
  ring 
  is 
  6*3 
  as 
  

   compared 
  with 
  15*08 
  before. 
  The 
  two 
  lower 
  atoms 
  take 
  

   positions 
  at 
  right 
  angles 
  to 
  the 
  upper 
  atoms, 
  thus 
  forming 
  a 
  

   tetrahedron, 
  of 
  four 
  hydrogen 
  atoms 
  with 
  one 
  carbon 
  atom 
  

   at 
  the 
  centre. 
  This 
  is 
  a 
  much 
  more 
  stable 
  arrangement 
  

   than 
  the 
  preceding 
  on 
  account 
  of 
  the 
  reduced 
  distances. 
  

   If 
  nitrogen 
  is 
  substituted 
  for 
  carbon 
  the 
  dimensions 
  all 
  

   increase 
  to 
  a 
  considerable 
  extent, 
  and 
  the 
  stability 
  di- 
  

   minishes, 
  as 
  in 
  the 
  case 
  of 
  the 
  ring 
  of 
  four 
  atoms 
  above. 
  

   This 
  combination 
  represents 
  the 
  compound 
  Methane 
  or 
  

   Marsh 
  gas, 
  perhaps 
  the 
  most 
  fundamental 
  of 
  the 
  very 
  great 
  

   family 
  of 
  hydrocarbon 
  compounds. 
  Special 
  graphical 
  

   methods 
  of 
  notation 
  for 
  this 
  family 
  are 
  used 
  in 
  Chemistry, 
  

   and 
  it 
  has 
  been 
  shown 
  that 
  there 
  are 
  compounds 
  which 
  

   demand 
  that 
  the 
  lines 
  of 
  connexion 
  between 
  the 
  different 
  

   atoms 
  must 
  be 
  represented 
  by 
  a 
  geometrical 
  figure 
  in 
  space 
  

   instead 
  of 
  one 
  in 
  a 
  plane. 
  Such 
  an 
  atom 
  as 
  this 
  in 
  the 
  

   tetrahedron 
  form 
  makes 
  the 
  reason 
  for 
  this 
  peculiarity 
  in 
  the 
  

   case 
  of 
  the 
  carbon 
  compounds 
  apparent. 
  

  

  Ions. 
  

  

  It 
  has 
  been 
  very 
  difficult 
  to 
  reconcile 
  the 
  theory, 
  at 
  the 
  

   present 
  time 
  much 
  in 
  vogue, 
  that 
  atoms 
  easily 
  gain 
  or 
  lose 
  

   electrons, 
  with 
  the 
  theory 
  of 
  the 
  formation 
  of 
  the 
  atoms 
  by 
  

   groups 
  of 
  electrons 
  in 
  stable 
  equilibrium 
  within 
  the 
  positive 
  

   sphere. 
  At 
  one 
  time 
  it 
  was 
  supposed 
  by 
  many 
  that 
  there 
  

  

  