DIFFUSION AND SUPERSATURATION IN GELATINE. 



By Harry W. Morse and George W. Pierce. 



Presented by J. Trowbridge, February 11, 1903. Received March 16, 1903. 



I. Introduction. 



The German photographer, R. Ed. Liesegang, in the course of a 

 research on chemical reactions in gelatine,* discovered a phenomenon 

 which Ostwald cites as evidence that there exists a definite limit beyond 

 which, at a given temperature and pressure, the supersaturation of a 

 solution cannot be carried. We have undertaken an experimental study 

 of this subject by a method based on Liesegang's discovery. 



Liesegang's experiment was as follows : A glass plate was covered with 

 gelatine impregnated with potassium chromate. The plate was laid hori- 

 zontal, and upon it a drop 

 of silver nitrate was placed. 

 The silver nitrate diffused 

 slowly out into the gelatine, 

 reacted with the potassium 

 chromate, and formed a pre- 

 cipitate of silver chromate. 

 The silver chromate, instead 

 of growing continuously in 

 the gelatine, as diffusion of 

 the reacting substances went 

 on, formed in distinct rings 

 about the drop, as shown in 

 Figure 1. The formation 

 of the precipitate in distinct 

 rings is clearly a phenome- 

 non of supersaturation. We 

 have undertaken certain 

 measurements of these rings in the hope of being able to obtain from them 

 some understanding of the conditions that exist in supersaturated solu- 



* Cltemische Reactionen in Gallcrten. Diisseldorf, 1898. 

 VOL. xxxviii. — 40 



Figure 1. 



