1153 



and Langmuir ^) on the condensation and reflection of metal vapours. 

 Knudsen assumes that reflection of melal vapour against the glass 

 wall is only possible when above a certain ciitical point and that 

 below this temperature the colliding molecules ai-e not reflected, but 

 remain fixed to the place where they strike the glass wall. 



Our observations concerning the iufluence of heating on already 

 existing deposits point out, that this view cannot be the right one. 



Far below the critical point, accepted by Knudsen the particles in 

 a very thin layer show very marked mobility, enabling them to 

 agglomerate into optically perceptible mici'ons (experiments with silver). 

 Hence a difference must be made between reflection against the glass 

 wall and mobility of the particles in the very thin layer of metal. 

 The latter continues to exist at a much lower temperature than the 

 former. 



Langmuir (I.e. 2253) observes as well that with irreversible subli- 

 mation, during which process the glass wall had such a low temperature 

 that no perceptible evaporation is possible, a sintering- or crystallisation- 

 process could take place. 



Langmuir (I.e. 2250) looks upon the collision of metalvapour-molec-ules 

 against solids such as glass as altogether non-elastic and on this 

 ground supposes pure reflection of metal vapour against the glasswall 

 to be exceptional. But the experiments bearing on the supersaturation 

 of Cd, Mg and Zn vapour indicate that such a reflection is quite 

 possible and may even give rise to a considerable supersaturation 

 of the raetalvapour. 



B. Colour of the metal-deposits. 



W, Mo, C, Fe, Fi, Pt produce colourless deposits; the other metals 

 produce a coloured film, which especially with Ag, An and Cu can 

 boast a great wealth of colour. 



This colouring capacity does not directly coincide with the structure 

 of the metal. On the one hand Au, Ag and Cu show both in their 

 deposits with mosaic-structure, being formed at room temperature 

 and in the structureless deposits being formed at a temperature of 

 liquid air, the same colour and the same sequence of colours, on 

 the other hand no colouring sets in with Pt, W, Fe, when the 

 structureless deposit of this local heating is orought to a mosaic 

 structure. 



It folloivs that the capacity of displaying colour is an individual 



1) Journ. Amer. Ghem. Soc. 38 (1916) 2221. 



