﻿Rhythmic 
  Precipitation. 
  25 
  

  

  This 
  is 
  surrounded 
  by 
  a 
  broad 
  clear 
  zone 
  marked 
  by 
  a 
  clearly 
  

   visible 
  circumferential 
  line. 
  The 
  nature 
  of 
  this 
  zone 
  is 
  un- 
  

   known, 
  at 
  present. 
  

  

  A 
  set 
  of 
  nine 
  diffusions 
  was 
  carried 
  out 
  with 
  5N, 
  2N 
  and 
  N 
  

   potassium 
  iodide 
  against 
  N/20, 
  N/40 
  and 
  N/80 
  lead 
  nitrate, 
  

   and 
  another 
  set 
  of 
  nine 
  with 
  2N, 
  N, 
  and 
  N/2 
  lead 
  nitrate 
  

   against 
  N/20, 
  N/40 
  and 
  N/80 
  potassium 
  iodide. 
  Probably 
  

   owing 
  to 
  the 
  state 
  of 
  the 
  gelatine 
  (not 
  thoroughly 
  free 
  from 
  

   acid) 
  the 
  precipitates 
  were 
  colloidal 
  and 
  not 
  visibly 
  banded 
  

   except 
  in 
  the 
  cases 
  of 
  2N 
  and 
  N 
  potassium 
  iodide 
  against 
  N/20 
  

   lead 
  nitrate, 
  which 
  showed 
  fine 
  rings 
  to 
  microscopical 
  examina- 
  

   tion. 
  They 
  all 
  showed 
  that 
  the 
  diffusion 
  proceeds 
  more 
  

   rapidly 
  with 
  greater 
  difference 
  of 
  concentrations 
  of 
  the 
  two 
  

   reagents 
  and 
  all 
  showed 
  a 
  broad 
  indefinite 
  band 
  around 
  the 
  

   drop 
  in 
  which 
  the 
  precipitate 
  was 
  thinner, 
  and 
  a 
  broad 
  band 
  

   on 
  the 
  outside 
  of 
  it 
  in 
  which 
  the 
  precipitate 
  was 
  thicker. 
  This 
  

   was 
  especially 
  marked 
  in 
  the 
  cases 
  where 
  potassium 
  iodide 
  was 
  

   the 
  diffusing 
  reagent 
  (the 
  one 
  in 
  the 
  drop). 
  It 
  was 
  found 
  that 
  

   several 
  of 
  these 
  plates 
  developed 
  a 
  banded 
  structure 
  imme- 
  

   diately 
  upon 
  being 
  immersed 
  in 
  a 
  solution 
  of 
  sodium 
  hydroxide, 
  

   which 
  was 
  used 
  to 
  clean 
  the 
  plates 
  after 
  they 
  had 
  dried. 
  Thus, 
  

   although 
  the 
  precipitate 
  is 
  present 
  in 
  colloidal 
  form 
  it 
  is 
  

   arranged 
  in 
  layers 
  or 
  bands, 
  though 
  these 
  are 
  invisible 
  until 
  

   some 
  such 
  reaction 
  as 
  that 
  described 
  shows 
  their 
  presence. 
  

  

  Effect 
  of 
  Different 
  Gelatine 
  Concentration. 
  

  

  The 
  reaction 
  4N 
  silver 
  nitrate 
  against 
  N/200 
  potassium 
  

   chromate 
  was 
  carried 
  out 
  in 
  gelatine 
  of 
  different 
  strengths, 
  

   obtained 
  by 
  dilution 
  of 
  the 
  one 
  stock. 
  Rings 
  were 
  formed, 
  

   and 
  the 
  rates 
  of 
  diffusion 
  were 
  measured. 
  The 
  plot 
  of 
  these 
  

   results 
  confirms 
  the 
  result 
  of 
  Hausmann 
  (loc. 
  cit.) 
  that 
  increase 
  

   of 
  the 
  gelatine 
  concentration 
  retards 
  the 
  diffusion. 
  

  

  The 
  curves 
  are 
  almost 
  parallel 
  and 
  the 
  rates 
  differ 
  so 
  slightly 
  

   that 
  the 
  curves 
  onty 
  begin 
  to 
  diverge 
  very 
  slightly 
  toward 
  the 
  

   right. 
  The 
  measurements 
  recorded 
  in 
  these 
  curves 
  are 
  only 
  

   rough, 
  but 
  they 
  suggest 
  that 
  more 
  careful 
  measurements 
  may 
  

   be 
  able 
  to 
  detect 
  a 
  numerical 
  relation 
  between 
  the 
  concentra- 
  

   tion 
  of 
  the 
  gelatine 
  and 
  the 
  amount 
  of 
  retardation. 
  

  

  Summary 
  and 
  Conclusions. 
  

  

  After 
  giving 
  a 
  historical 
  account 
  of 
  the 
  work 
  of 
  earlier 
  writ- 
  

   ers, 
  the 
  results 
  of 
  certain 
  experiments 
  are 
  given, 
  the 
  main 
  

   points 
  of 
  which 
  may 
  be 
  summarized 
  as 
  follows 
  : 
  

  

  1. 
  The 
  rate 
  of 
  diffusion 
  of 
  a 
  reagent 
  of 
  given 
  strength 
  is 
  

   retarded 
  by 
  increasing 
  that 
  of 
  the 
  reagent 
  in 
  the 
  gelatine. 
  

   Also, 
  the 
  total 
  distance 
  to 
  which 
  diffusion 
  takes 
  place 
  is 
  de- 
  

  

  