Chemistry. — " Ultramicroscopic investigation of very thhi m.etal- 

 fihns obtained by evaporation in high vacuum"". II. By Prof. 

 W. Reinders and L. Hamburger. (Communicated by Prof. 

 J. Böeseken). 



(Communicated in the meeting of September 29, 1917). 



Introductory. 



^1. In a previous paper ^) we staled tlie results of the ultra- 

 microscopic investigation of tlie extremely thin films of rock-salt, 

 silver, gold, and tungsten which are deposited on the glass wall of 

 the bulb either during evaporation in high vacuum or by means 

 of cathodic atomising. 



It appeared that the bright sublimate of sodiumchloride was 

 optically vacant and must be looked upon as a substance in the 

 amorphous-vitreous state. This state is metastable. Heating or the 

 access of moist air soon effects an opalescence, brought about by the 

 arising of small crystals, the growth of which can be investigated 

 under the ultraraicroscope. 



Of the metals, tungsten too gave a deposit similar to NaCl ; even 

 when so much of the metal had been sublimated, that the glass 

 had assumed a rather darkish tint, no structure could be observed 

 even under the most intense lighting. But gold and especially silver 

 formed a finely-coloured and distinct heterogenous deposit, that 

 showed itself under the microscope as a mosaic of small and variously- 

 coloured particles. The colour changed proportionally to the thickness 

 of the deposit and the heterogeneousness became more marked. 



The silver precipitate was like the salt precipitate highly susceptible 

 to the influence of a rise in temperature and moist air, which 

 immediately brought about a change in colour. In order to be able 

 to observe the precipitate in its original form it must be protected 

 from the influence of the air, in which we succeeded by covering 

 it, when still in the vacuum, by a thin layer of Canadabalsam. 

 In comparing the covered (with Can. B.) and non-covered precipitates 

 it appeared that the effect of the air causes a considerable coarsening 

 of the precipitate and thai the original, well-preserved precipitate" 

 showed a but scarcely perceptible heterogeneity. We still add in 



I) These Proceedinsg 19 (1916) 958. 



