|
|
 |
| |
- Raphael Eduard Liesegang (1869-1947)
- firstly discovered in 1896
- diffusion à chemical reaction à precipitation
- same processes are a possible explanation for some of the banding patterns in minerals and rocks
- solution of silver nitrate is placed on top of a gelatin gel containing potassium dichromate. The silver cation diffuses into the gel and reacts with the dichromate anion to produce a dark red precipitate of silver chromate:
4Ag+ + Cr2O7-2 + H2O -----> 2Ag2CrO4 + 2H+
- simplistically, one would expect a continuously expanding zone of precipitate to extend outward from the Ag+ source (as in diagram A). What we see, however, are discrete bands separated by spaces without any precipitate -- Liesegang rings (as in diagram B). Over the century since Liesegang's original study, a comprehensive explanation still has not been found.
formation of helix, then this breaks up into rings
|
|
|
 |
|
