1136 



fig. 1 and 2 (plate 1) a couple of photographic representations 

 bearing on this statement. 



It now occurred to us whether the silver, too, like NaCl and 

 tungsten was initially precipitated in a structureless state and was 

 caused to crystallize but afterwards and by secondary causes such 

 as heating. In this connection experiments were made, in which the 

 sublimate was formed extremely slowly and the glass-wall was 

 cooled down during the whole process of the sublimation to the 

 temperature of liquid air. Though under these circumstances the 

 crystallisation of the precipitate was greatly impeded, yet no structure- 

 less precipitate could be obtained. 



From this we see that silver passes very easily into the crystallised 

 state. But how do the other metals behave? Under what conditions 

 is a structureless deposit developed and when are heterogeneous 

 particles formed? Which metals reveal, like gold and silver, when 

 in very thin layers, definite colours; is tiiis property chiefly decided 

 by the thickness of the layer and the degree of dispersion of the 

 metal, independent of the nature of the latter, or must the* cause 

 be looked for in the very nature i.e. in the selective absorption of 

 the metal itself. 



In order to find the answer to these various questions we have 

 continued and enlarged our former investigations and shall relate 

 the results in the following pages. 



The Ultramicroscopic Investigation. 



§ 2. The apparatus. 



The tested elements, in the shape of thin filaments weie wrapped 

 on the support of an incandescent lamp where they were heated by 

 means of an electric current and brought into a state of evaporation, 

 after careful evacuation of the lamp. In most cases theie was fused 

 to the iamp a side-tube {b) with Canadabalsam, which had previously 

 been freed from the dissolved gases' and which was kept immeised 

 in liquid air during the time of burning of the lamp. When a 

 metal-sublimate had formed on the glass of (c), the Canadabalsam 

 was melted and carefully spread over the surface. 



The inner wall of the glass had been carefully cleaned — in 

 order to obtain a greater possibility of avoiding any disturbance in 

 the ultramicroscopic investigation arising from dust particles. 



As it was known besides that traces of remaining gases have a 

 great influence on the evaporation of a metal ^) and as it proved 



1) I. Langmuir, Trans. Amer. hist, of Electr. Eng. 1913, 1902. 



