﻿6 
  J. 
  Stansjield 
  — 
  Retarded 
  Diffusion 
  and 
  

  

  separate 
  the 
  ends 
  of 
  bands 
  without 
  the 
  formation 
  of 
  precipi- 
  

   tate 
  by 
  "sowing." 
  The 
  formation 
  of 
  the 
  rings 
  is 
  due 
  to 
  the 
  

   production 
  of 
  super-saturation 
  at 
  innumerable 
  individual 
  

   points. 
  Thus 
  the 
  spiral 
  form 
  does 
  not 
  afford 
  any 
  difficulty 
  to 
  

   the 
  super-saturation 
  hypothesis. 
  

  

  Bradford 
  (10) 
  has 
  recently 
  investigated 
  the 
  effect 
  of 
  the 
  by- 
  

   products 
  of 
  the 
  reactions 
  resulting 
  in 
  the 
  formation 
  of 
  the 
  ring 
  

   precipitates, 
  and 
  by 
  varying 
  the 
  concentration 
  of 
  the 
  by-pro- 
  

   duct 
  was 
  unable 
  to 
  affect 
  their 
  formation 
  in 
  any 
  way. 
  Hat- 
  

   schek 
  had 
  shown 
  that 
  the 
  particles 
  formed 
  in 
  the 
  ring 
  

   precipitates 
  are 
  larger 
  than 
  those 
  obtainable 
  in 
  aqueous 
  solu- 
  

   tions. 
  Bradford 
  suggests 
  that 
  this 
  phenomenon 
  is 
  due 
  to 
  

   adsorption 
  by 
  the 
  precipitate 
  of 
  substance 
  dissolved 
  in 
  the 
  gel, 
  

   which 
  merely 
  serves 
  to 
  retain 
  the 
  precipitate 
  in 
  place. 
  

  

  Bradford 
  finds 
  that 
  the 
  distances 
  between 
  the 
  layers 
  formed 
  

   are 
  roughly 
  inversely 
  proportional 
  to 
  the 
  molar 
  strength 
  of 
  the 
  

   reagent 
  in 
  the 
  gel, 
  and 
  not 
  to 
  that 
  of 
  the 
  diffusing 
  reagent. 
  

  

  In 
  a 
  more 
  recent 
  paper 
  (11) 
  the 
  same 
  author 
  has 
  developed 
  

   the 
  idea 
  of 
  adsorption 
  in 
  connection 
  with 
  the 
  formation 
  of 
  

   banded 
  precipitates. 
  It 
  might 
  be 
  suggested 
  that 
  the 
  term 
  

   pseudo-stratification 
  would 
  be 
  preferable 
  to 
  stratification 
  as 
  used 
  

   by 
  him. 
  

  

  Retarded 
  Diffusion 
  and 
  Rhythmic 
  Precipitation. 
  

  

  By 
  reason 
  of 
  its 
  application 
  to 
  geology 
  the 
  subject 
  of 
  

   rhythmic 
  precipitation 
  has 
  assumed 
  an 
  importance 
  to 
  geologists 
  

   which 
  cannot 
  be 
  neglected. 
  In 
  connection 
  with 
  an 
  investiga- 
  

   tion 
  of 
  Eozoon 
  the 
  writer 
  had 
  occasion 
  to 
  consider 
  the 
  question 
  

   of 
  the 
  causes 
  governing 
  the 
  formation 
  of 
  rhythmic 
  precipitates. 
  

   A 
  series 
  of 
  experiments 
  has 
  been 
  made 
  in 
  order 
  to 
  afford 
  a 
  

   basis 
  for 
  a 
  comparison 
  with 
  banded 
  structures 
  in 
  rocks. 
  The 
  

   experiments 
  were 
  carried 
  out 
  using 
  diffusion 
  from 
  a 
  drop 
  

   placed 
  upon 
  a 
  gelatine 
  layer 
  on 
  a 
  glass 
  plate, 
  as 
  described 
  by 
  

   Liesegang. 
  The 
  gelatine 
  was 
  prepared 
  according 
  to 
  his 
  direc- 
  

   tions 
  by 
  preparatory 
  washing 
  in 
  several 
  portions 
  of 
  distilled 
  

   water, 
  to 
  remove 
  some 
  but 
  not 
  all 
  of 
  the 
  impurities, 
  then 
  dis- 
  

   solving 
  in 
  distilled 
  water, 
  a 
  convenient 
  concentration 
  for 
  use 
  at 
  

   a 
  room 
  temperature 
  of 
  12° 
  C. 
  being 
  1 
  gr. 
  of 
  gelatine 
  in 
  35 
  c.c. 
  

   water. 
  The 
  solution 
  was 
  used 
  after 
  standing 
  one 
  or 
  two 
  days, 
  

   reheating 
  the 
  jellied 
  mass 
  to 
  bring 
  it 
  to 
  the 
  liquid 
  state 
  again, 
  

   care 
  being 
  taken 
  both 
  in 
  the 
  solution 
  and 
  re-solution 
  of 
  the 
  

   gelatine 
  to 
  avoid 
  over-heating. 
  Care 
  was 
  taken 
  to 
  keep 
  the 
  

   relative 
  gelatine 
  concentrations 
  the 
  same 
  in 
  any 
  set 
  of 
  experi- 
  

   ments. 
  This 
  was 
  done 
  by 
  adding 
  1 
  c.c. 
  of 
  a 
  solution 
  ten 
  times 
  as 
  

   strong 
  as 
  the 
  one 
  to 
  be 
  investigated 
  to 
  9 
  c.c. 
  of 
  the 
  gelatine 
  solu- 
  

   tion. 
  Thus 
  a 
  gelatine 
  solution 
  of 
  known 
  strength 
  was 
  obtained, 
  

   containing 
  any 
  desired 
  concentration 
  of 
  the 
  reagent 
  to 
  be 
  exam- 
  

  

  