﻿Rhythmic 
  Precipitation. 
  7 
  

  

  ined. 
  This 
  was 
  poured 
  out 
  on 
  to 
  several 
  glass 
  plates 
  and 
  allowed 
  

   to 
  set, 
  after 
  which 
  drops 
  of 
  the 
  second 
  reagent, 
  of 
  different 
  

   strengths, 
  were 
  placed 
  upon 
  them. 
  These 
  solutions 
  gradually 
  

   diffused 
  through 
  the 
  gelatine 
  and 
  precipitates 
  were 
  formed, 
  

   sometimes 
  continuously, 
  sometimes 
  in 
  separated 
  bands. 
  (See 
  

   figs. 
  1, 
  2, 
  and 
  3.) 
  

  

  It 
  is 
  found 
  that 
  with 
  different 
  concentrations 
  of 
  the 
  diffus- 
  

   ing 
  reagent 
  (the 
  one 
  in 
  the 
  drop) 
  against 
  a 
  constant 
  concentra- 
  

   tion 
  of 
  the 
  reagent 
  in 
  the 
  gelatine 
  the 
  diffusion 
  goes 
  at 
  

   different 
  rates, 
  the 
  stronger 
  solutions 
  diffusing 
  more 
  quickly 
  

   and 
  to 
  greater 
  distances 
  than 
  the 
  weaker. 
  Again, 
  by 
  keeping 
  

   the 
  diffusing 
  reagent 
  constant 
  and 
  varying 
  the 
  concentration 
  

   of 
  the 
  opposing 
  reagent 
  the 
  diffusion 
  is 
  retarded 
  by 
  increasing 
  

   the 
  opposing 
  concentration, 
  and 
  also 
  the 
  total 
  distance 
  of 
  dif- 
  

   fusion 
  is 
  decreased. 
  When 
  the 
  molecular 
  concentrations 
  of 
  

   the 
  solutions 
  approach 
  closely 
  there 
  is 
  a 
  definite 
  limit 
  to 
  the 
  

   distance 
  to 
  which 
  the 
  stronger 
  solution 
  is 
  able 
  to 
  diffuse. 
  In 
  

   many 
  of 
  the 
  experiments 
  the 
  gelatine 
  dried 
  before 
  the 
  limit 
  

   was 
  reached, 
  if 
  any 
  exists, 
  with 
  the 
  solutions 
  of 
  more 
  unequal 
  

   concentrations, 
  but 
  with 
  the 
  solutions 
  mentioned 
  above 
  the 
  

   limit 
  was 
  clear, 
  and 
  was 
  reached, 
  in 
  many 
  cases, 
  within 
  a 
  few 
  

   hours. 
  

  

  The 
  following 
  tables 
  for 
  different 
  experiments, 
  showing 
  the 
  

   distances 
  to 
  which 
  diffusion 
  has 
  taken 
  place 
  with 
  different 
  

   strengths 
  of 
  the 
  reacting 
  solutions, 
  illustrates 
  the 
  point. 
  The 
  

   figures 
  enclosed 
  in 
  a 
  double 
  line 
  are 
  for 
  experiments 
  using 
  one 
  

   batch 
  of 
  gelatine 
  and 
  are 
  comparable 
  with 
  each 
  other, 
  but 
  not 
  

   strictly 
  comparable 
  with 
  those 
  within 
  another 
  double 
  line, 
  by 
  

   reason 
  of 
  possible 
  differences 
  in 
  the 
  preparation 
  of 
  the 
  gela- 
  

   tine. 
  

  

  The 
  experiments 
  which 
  yielded 
  clearly 
  separated 
  bands 
  of 
  

   precipitate 
  are 
  indicated 
  by 
  a 
  small 
  ring 
  within 
  the 
  squares 
  

   belonging 
  to 
  them. 
  It 
  is 
  seen 
  that 
  the 
  production 
  of 
  the 
  bands 
  

   in 
  gelatine 
  takes 
  place 
  best 
  when 
  a 
  strong 
  silver 
  solution 
  dif- 
  

   fuses 
  against 
  a 
  weak 
  chromate 
  solution. 
  In 
  those 
  cases 
  which 
  

   did 
  not 
  show 
  clearly 
  separated 
  bands, 
  the 
  precipitate 
  appeared 
  

   to 
  be 
  continuous, 
  but 
  examination 
  with 
  the 
  hand 
  lens 
  or 
  some- 
  

   times 
  with 
  the 
  microscope 
  showed 
  that 
  the 
  bands 
  were 
  present, 
  

   but 
  that 
  they 
  were 
  more 
  closely 
  spaced, 
  so 
  as 
  to 
  appear 
  con- 
  

   tinuous. 
  Some 
  cases 
  are 
  clearly 
  banded, 
  to 
  the 
  naked 
  eye, 
  but 
  

   with 
  the 
  stronger 
  solutions 
  this 
  fine 
  banding 
  of 
  the 
  apparently 
  

   uniform 
  silver 
  chromate 
  can 
  only 
  be 
  seen 
  under 
  the 
  micro- 
  

   scope. 
  

  

  When 
  clearly 
  separated 
  bands 
  are 
  formed, 
  our 
  experiments 
  

   have 
  sometimes 
  shown 
  these 
  passing 
  into 
  fragmentary 
  banded 
  

   layers 
  toward 
  the 
  outside. 
  In 
  some 
  cases 
  this 
  may 
  be 
  quite 
  

   extensive, 
  corresponding 
  to 
  ten 
  or 
  more 
  bands. 
  In 
  other 
  cases, 
  

  

  