﻿14: 
  

  

  J. 
  Stansfield 
  — 
  Retarded 
  Diffusion 
  and 
  

  

  small 
  cloud 
  of 
  grannies, 
  but 
  along 
  the 
  line 
  of 
  the 
  band, 
  another 
  

   cloud 
  may 
  appear, 
  more 
  thickly 
  crowded 
  with 
  granules 
  in 
  the 
  

   central 
  line 
  of 
  the 
  band. 
  This 
  would 
  develop 
  as 
  before, 
  in 
  

   both 
  directions, 
  finally 
  uniting 
  with 
  the 
  other 
  advancing 
  part. 
  

   The 
  precipitate 
  on 
  each 
  side 
  of 
  the 
  central 
  part 
  gradually 
  

   thickened. 
  Thus, 
  while 
  the 
  result 
  is 
  a 
  series 
  of 
  bands 
  of 
  pre- 
  

  

  Fig. 
  4. 
  

  

  Fig. 
  4. 
  x 
  2 
  1/4. 
  The 
  result 
  of 
  the 
  diffusion 
  of 
  N/10 
  potassium 
  chrornate 
  

   into 
  a 
  gelatine 
  containing 
  N/100 
  silver 
  nitrate. 
  (No. 
  19.) 
  There 
  is 
  an 
  inner 
  

   set 
  of 
  close 
  bands 
  round 
  the 
  drop, 
  which 
  appear 
  to 
  be 
  continuous 
  precipi- 
  

   tate, 
  in 
  the 
  photograph 
  : 
  outside 
  this 
  zone 
  is 
  one 
  in 
  which 
  the 
  precipitate 
  

   occurs 
  as 
  isolated 
  granules, 
  and 
  this 
  is 
  followed 
  by 
  bands 
  in 
  which 
  the 
  pre- 
  

   cipitate 
  consists 
  of 
  separate 
  large 
  granules. 
  Examination 
  with 
  a 
  lens 
  will 
  

   show 
  this. 
  The 
  outer 
  bands 
  are 
  broken 
  by 
  clear 
  channels, 
  the 
  bands 
  being 
  

   offset 
  with 
  regard 
  to 
  each 
  other 
  on 
  opposite 
  sides 
  of 
  the 
  channels, 
  in 
  some 
  

   cases. 
  Both 
  the 
  inner 
  and 
  outer 
  sets 
  of 
  bands 
  become 
  more 
  widely 
  spaced 
  

   outwards. 
  

  

  cipitate, 
  of 
  apparently 
  striking 
  regularity, 
  yet 
  each 
  separate 
  

   small 
  portion 
  is 
  developed 
  independently 
  of 
  the 
  rest 
  at 
  such 
  

   point 
  as 
  the 
  super-saturation 
  boundary 
  is 
  over-stepped. 
  We 
  

   are 
  able 
  to 
  understand 
  more 
  clearly, 
  now, 
  how 
  the 
  development 
  

   of 
  spiral 
  forms 
  may 
  ensue, 
  and 
  how 
  breaks 
  may 
  occur 
  in 
  the 
  

   bands, 
  with 
  accompanying 
  displacement 
  of 
  the 
  bands 
  (see 
  

   fig. 
  4), 
  and 
  also 
  the 
  presence 
  of 
  cracks 
  passing 
  through 
  the 
  

   bands, 
  which 
  are 
  free 
  from 
  precipitate, 
  and 
  along 
  both 
  sides 
  of 
  

  

  