958 
Chemistry. — “Ultramicroscopic investigation of very thin metal 
and saltfilms obtained by evaporation in high vacuum”. By 
Prof. W. Reinpers and L. HAMBURGER. (Communicated by 
Prof. J. BörsFKEN). 
(Communicated in the meeting of October 28, 1916). 
It is a well-known fact, that the blackening of incandescent 
lamps must be attributed to the slow sublimation of the material 
used for filament, which settles on the bulb as a very slight deposit, 
‘and becomes darker proportional to the time of incandescence. 
Thin deposits on the bulb may be obtained in this manner, not 
only of carbon, tantalum and tungsten, but also of other metals 
such as silver and gold * and as one of us has described?) — 
even of metal-compounds (NaCl, Na,O, NaOH, Na,WO, ete), when 
they are brought to a lower or higher rate of incandescence in the 
high vacuum of the incandescent Jamp. 
Whereas the films of carbon, tantalum and tungsten are black, 
those of silver and gold are coloured and the salts form an absolutely 
colourless, clear deposit, which is invisible to the eye, as long as 
it remains in the same condition. 
We have subjected these films to an ultramicroscopic investigation, 
the results of which we shall communicate in the following pages. 
Rock-salt. This deposit was obtained by heating in high vacuum 
(0.0003 to 0.0010 mm.) a tungsten filament, which had been 
fixed in an ineandescent lamp in the usual manner and had been 
partially covered with solid NaCl. Before the connection with the 
air-pump had been broken by melting off, the lamp had been heated 
to 380° C. in order to exhaust the gases from the bulb. 
As long as the vacuum is maintained, the salt-deposit is perfectly 
clear and colourless, so that it is imperceptible to the eye. When 
the lamp is opened, so that the moist air can enter, the deposit 
soon becomes opalescent and especially after the lapse of some time 
this phenomenon becomes more pronounced. When a bit of the 
bulb was brought under the ultramicroscope®), as soon as possible 
1) M. Farapay. Phil. Trans. Roy. Soc. London 147, 145 (1857). 
G. T. Bempy. Proc. Roy. Soc. London 72, 226, (1903). 
L. HouLLeEvIGvVE. Ann. chem. et phys. (8) 20, 138 (1910). 
2) L. HAMBURGER. Chem. Weekbl. 13 (1916), 535. 
3) Cardioid condenser, Special object glass V of Zeiss, Compensation ocular 18, 
glycerine-immersion. 
