292 Mr. J. H. T. Roberts on the 



volatilizing, contrary to Owen and Hughes' result with 

 solid 00 2 *. 



I£ the palladium volatilizes rapidly in a vacuum, it might 

 be expected that the bright metallic deposit would prove to 

 be crystalline. Examined under the microscope, however,, 

 it was found to be perfectly uniform ; there were no holes, 

 and yet the film was semi-transparent. A careful microscopic 

 examination of the glowing wire, in this and in other cases, 

 did not reveal any of the glowing particles mentioned by 

 Keboul and Bollemont. In order to see if crystalline 

 structure in the film was to be expected as a necessary 

 result of sublimation, I made a test in which the deposit 

 was known to be the result of sublimation. I fused a 

 palladium wire in a vacuum, and the surface of the glass 

 was instantly covered with a perfect bright palladium 

 mirror, which under the microscope showed no signs what- 

 ever of crystallization ; the microscope used in all these 

 experiments was a high power Zeiss with vertical illuminator. 

 Examination of the fused wire at the point of fusion showed 

 that the metal was covered with small mounds as though 

 it had boiled ; there was no evidence of crystallization here. 

 Probably the reason that these deposits are not crystalline is 

 that the vapour has been in too rapid motion, and has 

 been cooled too quickly. In platinum resistance furnaces 

 the vapour produced by the dissociation of the volatile oxide 

 of the platinum is entirely confined, and almost stationary ; 

 it therefore slowly condenses upon the hot clay cylinder of 

 the furnace in the form of crystals. 



On dipping pieces of the broken glass, having these 

 deposits, into nitric acid, the palladium films were instantly 

 dissolved, and produced the usual bronze coloration of the 

 acid. Three samples of the palladium films were heated 

 (1) moderately with a bunsen, (2) strongly with bunsen,. 

 (3) strongly in blow-flame. On examining these in the 

 microscope 1 and 2 showed no special features, but 3 

 had a fern-like pattern depending upon crystallic action, 

 though no individual crystals were seen f . 



* Phil. Mag. 1908. 



t It is impossible to exaggerate the "beauty of these films as seen in 

 the microscope. The patterns are similar to those produced by frost 

 upon glass, and interference colours are seen by transmitted light. If 

 the film is gently breathed upon, the patterns go through most beautiful 

 transformations, both as to colour and arrangement, these effects being 

 due to the thickening and distortion of the film with the heat of the 

 breath. 



