﻿18 
  

  

  J. 
  Stansfteld 
  — 
  Retarded 
  Diffusion 
  and 
  

  

  ditions, 
  such 
  as 
  gelatine 
  concentration 
  and 
  amount 
  of 
  acid 
  or 
  

   other 
  solute 
  present, 
  remain 
  constant 
  the 
  distance 
  between 
  the 
  

   rings 
  depends 
  upon 
  the 
  ionic 
  concentrations 
  and 
  also 
  upon 
  the 
  

   relative 
  rates 
  of 
  diffusion. 
  It 
  thus 
  appears 
  that 
  if 
  in 
  any 
  reac- 
  

   tion 
  the 
  increase 
  in 
  distance 
  between 
  the 
  bands 
  due 
  to 
  the 
  effect 
  

   of 
  the 
  difference 
  of 
  rates 
  of 
  diffusion 
  could 
  be 
  counter-balanced 
  

   by 
  an 
  equal 
  effect 
  in 
  the 
  opposite 
  direction 
  due 
  to 
  concentra- 
  

   tions, 
  the 
  s}3aces 
  between 
  the 
  bands 
  would 
  remain 
  constant. 
  

  

  Fig. 
  8. 
  

  

  I 
  cm. 
  

  

  uj.4 
  

  

  Z 
  

   < 
  

  

  P 
  

  

  

  ■fiL 
  K 
  2 
  G0 
  4 
  

  

  zoo 
  2 
  * 
  

  

  to 
  *M 
  

  

  20 
  z 
  * 
  

  

  Ikr. 
  Z 
  3 
  4 
  5" 
  6 
  

  

  Fig. 
  8. 
  Diffusion 
  of 
  normal 
  lead 
  nitrate 
  against 
  potassium 
  chromate 
  of 
  

   different 
  strengths. 
  

  

  Agate 
  structure 
  has 
  been 
  ascribed 
  to 
  the 
  formation 
  of 
  Liese- 
  

   gang 
  rings 
  by 
  diffusion 
  of 
  solutions 
  through 
  gelatinous 
  silica. 
  

   The 
  discovery 
  of 
  gelatinous 
  silica 
  in 
  a 
  cavity 
  in 
  the 
  Simplon 
  

   tunnel 
  is 
  of 
  interest 
  in 
  this 
  connection. 
  On 
  examining 
  certain 
  

   agates 
  the 
  writer 
  was 
  struck 
  by 
  the 
  fact 
  that 
  many 
  of 
  them 
  

   show 
  bands 
  ichich 
  are 
  equally 
  spaced 
  and 
  not 
  at 
  successively 
  

   increasing 
  distances, 
  as 
  in 
  the 
  ordinary 
  Liesegang 
  rings. 
  

  

  The 
  writer 
  does 
  not 
  consider 
  that 
  agates 
  in 
  general 
  can 
  be 
  

   held 
  to 
  be 
  produced 
  by 
  the 
  Liesegang 
  reaction 
  ; 
  out 
  of 
  a 
  large 
  

   number 
  examined 
  but 
  very 
  few 
  seem 
  to 
  be 
  explicable 
  only 
  

   along 
  these 
  lines, 
  by 
  far 
  the 
  greater 
  number 
  allowing 
  of 
  other 
  

   explanations. 
  Each 
  specimen 
  of 
  agate 
  needs 
  to 
  be 
  examined 
  

   by 
  itself, 
  the 
  history 
  of 
  each 
  one 
  being, 
  of 
  necessity, 
  a 
  separate 
  

   entity, 
  and 
  only 
  comparable 
  with 
  others 
  by 
  an 
  accidental 
  repro- 
  

   duction 
  of 
  a 
  similar 
  series 
  of 
  events. 
  

  

  