1147 



sublimation produced a less thick, beautiful, blue precipitate, which 

 was covered with Cauadabalsam when in vacuum. It revealed 

 typical conglomerates of circularly-placed particles, in the neighbour- 

 hood of which the field was exhausted, being elsewhere set with 

 fairly large ultramicrons (cf. fig. 5 Plate I). 



Cd. vapour condenses uiore readily on copper and on lead than 

 on glass. 



^ 14. Magnesium. 



This too, shows the symtoras of supersaturation, which were 

 observed with cadmium. Therefore the lamp was kept immersed 

 in liquid air during the entire time of burning. The precipitate is 

 highly metallic-reflecting and blue with transmitted light. Under the 

 microscope we observe in a mosaic of weaker, for the greater part 

 yellow-coloured particles, a number of larger separately-situated 

 particles, which are much more luminous. 



^ 15. Zinc. 



This metal shows, like Cd and Mg, at roomtemperature symptoms 

 of supersaturation, hence I he precipitate was obtained once more at 

 a temperature of liquid aii-. It was blue with transmitted light. The 

 microscopic field was entirely occupied with extremely fine nearly 

 invisible particles, among which were regular circles of small con- 

 glomerates. In this respect it bears a close resemblance to cadmium. 



Measurements of the Electric Conductivity. 



As the observations of the colour and the conclusions drawn 

 from them concerning alterations in the thin layers of metal are 

 accompanied by the error of subjectiveness and the drawback that these 

 alterations cannot be expressed in figures, we tried to obtain 

 more positive facts by measurements of the electric conductivity. 

 These measurements have this advantage that they can be executed 

 in the vacuum and hence enable us to become acquainted with 

 the possible influence of the layer CaF, and Cauadabalsam. This 

 wish, to obtain a closer control about a possible influence of the 

 protecting layers was the direct motive for the sul^sequent 

 conductivity measurements. Our method of measuring was the same 

 as the one Messrs. S. Webkr and E. Oosterhuis followed with their 

 investigation about the connection between the electric resistance 

 and the thickness of the layers of metal ^). In the execution of the 



^) These Proceedings XIX (1916), p. 597. 



