1152 



By means of Fieating, an alread}' formed and optically insoluble 

 precipitate obtaijis distinct heterogeoiisness and mosaie-striioture. This 

 could be observed particularly well with Ag, Au, Pt, Fe and Wo. 

 The conduct of molybdenum is somewhat divergent, because here 

 the particles show an inclination towards arrangement into larger 

 conglomerates, circles or straight lines, making the impression of 

 inchoating crystallization. 



With the lower melting metals — Cd, Zn, Mg — as well 

 higher condensation temperature results in a coarsening of structure. 

 If we compare the condensates, which Kohlschütteii and Ehlers') 

 obtained with Zn, Cd and As, with those originating during our 

 experiments, it will appear that the latter are ever so much finer. 

 With the experiments of Kohlschütter and Ehlers the metal was 

 one-sidedly heated in an evacuated tube of hard fusible glass or 

 of quartz in an electric furnace and the condensate that was 

 deposited in a colder part of the tube, was examined. It stands 

 to reason that the temperature of the glasswall in this colder 

 part is far above room temperature, wiiile with our experiments 

 the glasswall was refrigerated in liquid air. K. and E. obtained 

 distinctly separate particles, from 0.01 to 0.05 mm. diameter, whereas 

 with our experiments the dimensions were ten and even more times 

 smaller. Otherwise they too determined with these metals the circles 

 of larger particles which had grown at the expense of the neigh- 

 bouring smaller ones. 



Mindful of the condensation-temperature we can enlarge the above 

 mentioned conclusion and formulate it as follows : The structure óf 

 the deposit formed is coarser in the same proportion as ivith the 

 vapour tension of this metal, at the temperature of the ivall, against 

 which a metal vapour condenses, is greater. 



The succession in which this coarsening is observed is as follows: 

 1. the precipitate is optically insoluble; 2. the precipitate is for the 

 greater part optically insoluble but also shows larger separate particles; 

 3. instead of the homogeneous, optically insoluble part a connected 

 network of more or less strong ultramicrons sets in; 4. the ultra- 

 microns of the network become larger and more separate; 5. the 

 smaller particles are distinctly separate and occasionally show 

 conglomeration, inchoating crystal-structure or the growth of some 

 larger ones at the expense of surrounding smaller ones. 



Let us now test our experiments to the observations ofKNUDSEN') 



1) Z.f. Elektrochemie 18 (1913) 373. 



2) Ann. der Physik. (4) 50 (1916) 472. 



