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Prof. A. B. Macallum and Miss M. L. Menten. [July 24, 



which, however, is not deposited uniformly, hut in rings, all concentric also, 

 each separated from its neighbour on both sides by clear zones free, or 

 almost free, from silver chromate. These zones increase in width from the 

 centre to the periphery. When the bichromate-holding gelatine is in open 

 capillary tubes the silver salt penetrates, and as it diffuses in silver 

 chromate-holding zones, develops alternately with silver chromate-free bands, 

 and the latter increase in width with the distance from the point of 

 penetration, i.e., the open end of the capillary tube. 



The phenomenon found by Boehm was explained by Boveri as indicated in 

 the section on the literature. Ostwald* has applied to Liesegang's rings the 

 explanation that in the diffusion of the silver salt and the consequent 

 formation of silver chromate, the metastable and labile conditions of 

 solutions of the latter salt alternately prevail, the metastable stage as it is 

 developing into the highest degree of supersaturation, i.e., the labile 

 condition, diffusing through an extent of the gelatine film or of the gelatine 

 column that is to constitute an interstriate zone. When the critical 

 concentration in the advancing solution is reached, then the precipitation 

 begins and continues, thus forming a stria. The precipitation brings the 

 solution back to the metastable condition, then another development into 

 the labile condition obtains and as before a new interstriate zone and a new 

 stria result. This process is repeated indefinitely so long as the diffusion 

 occurs, but as the silver salt becomes more and more dilute, critical con- 

 centration is later and later attained, and in consequence the new striae are 

 separated from each other by broader and broader interstriate intervals. 

 Also, although this is not included in Ostwald's explanation, the striae 

 themselves must, for the same reasons, become broader but less pronounced 

 in density. 



Ostwald's explanation is accepted by Morse and Pierce,f who, working on 

 the rate of diffusion in capillary tubes filled with chromate-holding gelatine 

 when placed in silver nitrate solutions, found xj\/ i is a constant. The 

 phenomenon has also been studied by HausmannJ who determined that the 

 rate of formation of the precipitate is nearly proportional to the rate of 

 diffusion of the ions of the salts concerned, and in consequence it has been 

 suggested that the rate of precipitation be taken as a measure of the 



* ' Zeit. fur physik. Chem.,' vol. 22, p. 302, 1897, and vol. 23, p. 365, 1898 ; also 

 ' Lehrbueh der allgem. Chemie,' 2 Aufl., vol. 2, p. 778. 



t "Diffusion und Uberssittigung in Gelatine," 'Zeit. fiir physik. Chem.,' vol. 45, 

 p. 589, 1903. 



% " Uber Niederschlagebildungen in Gallerten," ' Zeit. fiir anorg. Chem.,' vol. 40, 

 p. 110, 1904 



