ON THE LIESEGANG PHENOMENON 



IN GELS 



By S. C. BRADFORD, B.Sc. 



The Science Museum, South Kensington, London 



The observation was made by Liesegang in 1896 that, when a 

 drop of silver nitrate solution is placed on a gelatin film con- 

 taining potassium bichromate, the silver bichromate formed is not 

 distributed throughout the gelatin, but is deposited in concentric 

 rings around the drop. The phenomenon has been studied by a 

 number of subsequent investigators in the hope of throwing 

 light on the structure of gels. In later researches the gel is 

 usually contained in a test-tube, and the solution of reacting 

 substance poured on top. The precipitation takes place in 

 strata extending down the tube. Ostwald explained the for- 

 mation of rings as the result of the sudden precipitation of a 

 supersaturated solution of silver bichromate. Bechhold made a 

 number of experiments in 1905, and showed that, in the case of 

 ammonium bichromate and silver nitrate, the precipitate is 

 more soluble in the ammonium nitrate resulting from the re- 

 action, and suggested that the ammonium nitrate formed might 

 prevent further precipitation in its immediate neighbourhood. 

 In a lecture at the Royal Institution in 191 2 Sir J.J. Thomson 

 proposed the theory that the soluble substances produced might 

 act in a similar way to certain bodies known as stabilisers which 

 prevent the precipitation of colloidal solutions. By diffusion 

 into the gel the concentration of these stabilisers would be 

 diminished and further deposition of the precipitate allowed. 

 Liesegang showed in 1907 that the intermediate spaces 

 between the rings contain no bichromate. Hatschek made a 

 great many experiments in 191 2, using a number of fresh com- 

 pounds. He showed that the particles of the precipitates pro- 

 duced are much larger than could be obtained in aqueous 

 solution, and explained, by his results, many features of the 

 occurrence of gold in quartz. Some further experiments were 



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