THE LINEAR FORCE OF GROWING CRYSTALS 327 



again, "On Adsorption and Saturated Surfaces" (1913), 1 without 

 developing any single fact in support of the hypothesis advanced 

 by Bruhns and Mecklenburg. 



Neither capillarity nor adsorption exerts any upward pressure 

 on the loaded disks of porcelain in the experiments under discus- 

 sion, while adsorption does not prevent the exercise of the very 

 great downward pressure due to the surface tension of water. Yet 

 the alum crystallized and the disks were raised. 



In the opinion of the observers it was essential to the elevation 

 of the disks that evaporation should be complete. 1 Was the eleva- 

 tion, then, produced after the crystallization was complete and the 

 mass solidified? The observers make no such statement, which, 

 indeed, would seem absurd. But if the raising was not effected 

 after solidification, it must have been produced before solidifica- 

 tion, or while the underlying film was liquid and while crystalliza- 

 tion was in progress, in opposition to capillary force as well as to 

 the weight of the disks and their load. 



Liesegang appears to have appreciated this anomaly in Bruhns 

 and Mecklenburg's statement, though accepting their conclusion, 

 for he sought to relieve it by the following explanation (referring 

 to the experiments of Bruhns and Mecklenburg) : " Nicht ein Wach- 

 stumsdruck der Krystalle sondern Capillar- und Adsorptionskrafte 

 bewirkten hier also die Hebung. Das heisst die Leistung war schon 

 volbracht ehe Kristalle auftraten." 2 "The lifting was done before 

 the crystals formed." This is not claimed by Bruhns and Meck- 

 lenburg, nor supported by any experimental evidence which they 



fact that this preliminary phenomenon is particularly sensitive to slight impurities 

 upon the crystal surface" (ibid., LXXIII [1910], 718). 



"No relation could be established between concentration and the quantity of 

 adsorbed material" (ibid., LXXIII [1910], 686). 



"In all cases the rate of crystallization is diminished by the addition of substances 

 which are adsorbed by the crystal, eventually even to the point of becoming practically 

 zero" (ibid., LXXIII [1910], 718). 



"It was shown that the substances chiefly adsorbed by crystals are colloids, while 

 the crystalloids are adsorbed only very slightly" (ibid., LXXXI [1913], 692). 



1 Bruhns and Mecklenburg, op. Git., p. 106: "Es sei aber ausdnicklich betont 

 dass der Versuch nicht gelang, wenn wir nicht die Masse bis zum Grunde trocken 

 werden liessen." 



2 R. E. Liesegang, " Kristallisationskraft," Naturw. Rundschau der Chem. Ztg., 

 Zweite Jahrg. 1913, p. 183. 



