﻿26 
  J. 
  Stansfield 
  — 
  Retarded 
  Diffusion. 
  

  

  creased 
  by 
  a 
  similar 
  increase 
  of 
  strength 
  of 
  the 
  reagent 
  in 
  the 
  

   gelatine. 
  

  

  2. 
  With 
  too 
  close 
  approach 
  of 
  the 
  concentrations 
  of 
  the 
  

   two 
  reagents, 
  silver 
  nitrate 
  and 
  potassium 
  chromate, 
  a 
  continuous 
  

   precipitate 
  is 
  formed, 
  but 
  under 
  the 
  microscope, 
  the 
  surface 
  of 
  

   this 
  is 
  seen 
  to 
  be 
  finely 
  banded. 
  These 
  fine 
  bands 
  follow 
  the 
  

   same 
  rules 
  as 
  regards 
  spacing 
  as 
  are 
  found 
  with 
  the 
  separated 
  

   bands. 
  

  

  3. 
  Separated 
  bands 
  are 
  best 
  produced 
  by 
  the 
  diffusion 
  of 
  a 
  

   strong 
  silver 
  solution 
  against 
  a 
  weak 
  chromate 
  solution. 
  (For 
  

   other 
  reagents, 
  these 
  conditions 
  may 
  not 
  be 
  universal.) 
  

  

  4. 
  Similar 
  results 
  are 
  obtained 
  by 
  diffusion 
  of 
  a 
  strong 
  

   chromate 
  solution 
  against 
  a 
  weak 
  silver 
  solution. 
  But 
  the 
  

   particles 
  formed 
  are 
  larger 
  in 
  this 
  case. 
  

  

  5. 
  Increase 
  in 
  distance 
  between 
  bands 
  has 
  been 
  held 
  to 
  be 
  

   due 
  to 
  progressive 
  dilution 
  of 
  the 
  reagents. 
  Rate 
  of 
  diffusion 
  

   is 
  shown 
  to 
  be 
  an 
  important 
  controlling 
  factor, 
  and 
  that 
  under 
  

   certain 
  conditions 
  the 
  bands 
  may 
  be 
  equally 
  spaced, 
  or 
  may 
  be 
  

   spaced 
  at 
  decreasing 
  distances. 
  These 
  conditions 
  are 
  discussed. 
  

  

  6. 
  The 
  rates 
  of 
  diffusion 
  of 
  different 
  reagents 
  in 
  pure 
  gela- 
  

   tine 
  are 
  found 
  to 
  differ; 
  thus 
  potassium 
  chromate 
  diffuses 
  more 
  

   rapidly 
  than 
  a 
  lead 
  nitrate 
  solution 
  of 
  the 
  same 
  molecular 
  con- 
  

   centration, 
  and 
  a 
  silver 
  nitrate 
  solution 
  more 
  rapidly 
  than 
  a 
  

   potassium 
  chromate 
  solution. 
  Also, 
  a 
  strong 
  solution 
  of 
  any 
  

   given 
  reagent 
  diffuses 
  more 
  rapidly 
  than 
  a 
  weak 
  solution. 
  

  

  Bibliography. 
  

  

  1. 
  Liesegang, 
  R. 
  E., 
  Chemical 
  Reactions 
  in 
  Gelatine. 
  Dusseldorf, 
  1898. 
  

  

  2. 
  Ostwald, 
  W., 
  Zeitscbr. 
  phys. 
  Chem., 
  vol. 
  xxiii, 
  1897, 
  p. 
  365. 
  

  

  3. 
  Morse, 
  H. 
  W., 
  and 
  Pierce, 
  G. 
  W.. 
  ibid., 
  vol. 
  xlv, 
  1903, 
  p. 
  589. 
  

  

  4. 
  Hausmann, 
  J., 
  Zeitscbr. 
  anorg. 
  Chem., 
  vol. 
  xl. 
  1904, 
  p. 
  110. 
  

  

  5. 
  Larsen, 
  Ann. 
  d. 
  Phys., 
  vol. 
  iv. 
  folge 
  9, 
  p. 
  1186. 
  

  

  6. 
  Bechhold, 
  H., 
  Zeitscbr. 
  phys. 
  Chem., 
  vol. 
  lii, 
  1905, 
  p. 
  185. 
  

  

  7. 
  Liesegang, 
  R. 
  E., 
  ibid., 
  vol. 
  lix, 
  1907, 
  p. 
  444. 
  

  

  8. 
  Hatscbek, 
  E., 
  Zeitschr. 
  Chem. 
  Ind. 
  Koll., 
  vol. 
  x, 
  1912, 
  p. 
  124. 
  

  

  9. 
  Liesegang, 
  R. 
  E., 
  Zeitschr. 
  phys. 
  Chem., 
  vol. 
  lxxxviii, 
  1914, 
  p. 
  1. 
  

  

  10. 
  Bradford, 
  S. 
  C, 
  Sci. 
  Prog., 
  vol. 
  x, 
  No. 
  39, 
  1916, 
  p. 
  369. 
  

  

  11. 
  Bradford, 
  S. 
  C, 
  Biochem. 
  Jour., 
  vol. 
  x, 
  1916, 
  p. 
  169. 
  

  

  