﻿Rhythmic 
  Precipitation. 
  9 
  

  

  tins 
  is 
  followed, 
  on 
  the 
  outside, 
  by 
  an 
  area 
  in 
  which 
  the 
  pre- 
  

   cipitate 
  occurs 
  as 
  a 
  continuous 
  non-banded 
  area 
  containing 
  the 
  

   precipitate 
  as 
  small 
  granules. 
  

  

  In 
  other 
  cases 
  the 
  fragmentation 
  is 
  not 
  so 
  prominent 
  and 
  

   the 
  non-banded 
  area 
  of 
  " 
  disseminated 
  " 
  precipitate 
  is 
  followed 
  

   outward 
  by 
  " 
  secondary 
  " 
  bands 
  of 
  precipitate, 
  which 
  differ 
  

   from 
  the 
  " 
  primary 
  " 
  ones 
  within, 
  in 
  that 
  they 
  are 
  evenly 
  

   spaced 
  and 
  not 
  farther 
  apart, 
  with 
  greater 
  distance 
  from 
  the 
  

   center, 
  and 
  in 
  being 
  made 
  up 
  of 
  large, 
  irregularly 
  shaped 
  

   grains 
  of 
  silver 
  chromate, 
  sometimes 
  separate 
  from 
  each 
  other, 
  

   whereas 
  the 
  " 
  primary 
  " 
  bands 
  are 
  continuous 
  and 
  consist 
  of 
  

   exceedingly 
  minute 
  granules 
  of 
  silver 
  chromate. 
  (See 
  fig. 
  1.) 
  

   There 
  is 
  always 
  a 
  clear 
  " 
  halo 
  " 
  outside 
  the 
  circle 
  of 
  diffusion 
  

   which 
  appears 
  to 
  be 
  free 
  from 
  precipitate, 
  but 
  under 
  the 
  micro- 
  

   scope 
  is 
  seen 
  to 
  contain 
  minute 
  grains 
  of 
  silver 
  chromate. 
  In 
  

   some 
  cases 
  " 
  subsidiary 
  " 
  bands 
  have 
  been 
  noticed 
  in 
  this 
  

   " 
  halo." 
  They 
  correspond 
  to 
  the 
  very 
  fine 
  lines 
  noticed 
  by 
  the 
  

   earlier 
  workers 
  and 
  ascribed, 
  by 
  them, 
  to 
  the 
  presence 
  of 
  

   impurities 
  in 
  the 
  gelatine. 
  

  

  A 
  set 
  of 
  experiments 
  was 
  made 
  with 
  silver 
  nitrate 
  in 
  the 
  

   gelatine 
  and 
  potassium 
  chromate 
  as 
  the 
  u 
  dominant 
  " 
  reagent 
  

   in 
  the 
  central 
  drop, 
  having 
  the 
  higher 
  molecular 
  concentration. 
  

   The 
  results 
  in 
  this 
  case 
  were 
  remarkablj 
  7 
  interesting. 
  The 
  fol- 
  

   lowing 
  table 
  gives 
  the 
  scheme 
  of 
  concentrations 
  used. 
  Numbers 
  

   26 
  to 
  30 
  showed 
  only 
  isolated 
  spots 
  or 
  grannies 
  formed 
  here 
  

   and 
  there 
  in 
  the 
  gelatine 
  as 
  the 
  chromate 
  diffused 
  outward. 
  

   Numbers 
  21 
  to 
  25 
  showed 
  the 
  beginning 
  of 
  a 
  very 
  indefinite 
  

   arrangement 
  of 
  the 
  spots 
  in 
  bands. 
  Numbers 
  16 
  to 
  20 
  showed 
  

   an 
  inner 
  set 
  of 
  apparently 
  continuous 
  bands 
  consisting 
  of 
  large 
  

   granules 
  of 
  silver 
  chromate 
  followed 
  by 
  a 
  space 
  with 
  the 
  pre- 
  

   cipitate 
  as 
  isolated 
  granules, 
  and 
  outside 
  this 
  again 
  the 
  arrange- 
  

   ment 
  in 
  bands 
  as 
  in 
  21 
  to 
  25, 
  but 
  more 
  clearly 
  shown. 
  (See 
  fig. 
  

   4.) 
  The 
  inner 
  bands 
  are 
  less 
  well 
  shown 
  the 
  stronger 
  the 
  chro- 
  

   mate 
  solution. 
  The 
  outer 
  bands 
  often 
  show 
  discontinuity 
  and 
  

  

  Table 
  (p. 
  8) 
  showing 
  distances 
  diffused 
  in 
  a 
  radial 
  direction, 
  measured 
  in 
  

   centimeters. 
  The 
  head 
  of 
  the 
  column 
  shows 
  the 
  strength 
  of 
  the 
  silver 
  nitrate 
  

   solution 
  diffusing 
  and 
  the 
  strength 
  of 
  the 
  potassium 
  chromate 
  solution 
  in 
  

   the 
  gelatine 
  is 
  indicated 
  at 
  the 
  extreme 
  right. 
  Upper 
  left 
  part 
  of 
  table 
  — 
  

   distances 
  diffused 
  after 
  6 
  hrs. 
  15 
  mins. 
  Upper 
  right, 
  after 
  6 
  hrs. 
  Lower 
  

   left, 
  after 
  1 
  hr. 
  50 
  mins. 
  Lower 
  right, 
  after 
  2 
  hrs. 
  

  

  The 
  results 
  which 
  show 
  discrepancies 
  are 
  indicated 
  by 
  parentheses. 
  These 
  

   are 
  due 
  to 
  inaccuracies 
  in 
  measurement. 
  Those 
  which 
  recur 
  in 
  the 
  

   same 
  positions 
  in 
  both 
  parts 
  of 
  the 
  table 
  are 
  due 
  to 
  incorrect 
  measurement 
  

   of 
  the 
  size 
  of 
  the 
  original 
  drop, 
  the 
  others 
  to 
  inaccuracies 
  in 
  those 
  individual 
  

   measurements. 
  The 
  figures 
  on 
  the 
  right 
  side 
  of 
  the 
  table 
  are 
  comparable 
  

   with 
  each 
  other, 
  and 
  those 
  on 
  the 
  left 
  side 
  with 
  each 
  other, 
  but 
  as 
  they 
  were 
  

   obtained 
  from 
  experiments 
  using 
  two 
  separately 
  prepared 
  batches 
  of 
  gela- 
  

   tine, 
  the 
  figures 
  on 
  the 
  left 
  are 
  not 
  comparable 
  with 
  those 
  on 
  the 
  right, 
  

   except 
  in 
  a 
  general 
  way. 
  

  

  