960 
3. Increase of thickness of the layer by more prolonged sublimation. 
Silver. Instead of the tungsten filament a thin wire of very pure 
silver had been fixed in an incandescent lamp. The lamp had been 
carefully exhausted with the help of liquid air, during which process it 
had been heated to 380° C, and during a short time the wire itself 
was kept at a low dnll-red beat by means of an electric current. 
Thus any impurities that might be found on the bulb and the wire 
were removed as well as possible. Hereupon the lamp was melted 
off. If now the filament was brought to a deep-red heat with the 
aid of the electric current a deposit soon appeared against the bulb. 
With a prolonged sublimation the colour of this deposit changed 
from an original pale yellow into orange-yellow, red, violet and 
finally into blue. 
On opening the lamp we observed as a rule a deepening of the 
colour, de. a change of colour trending to yellow-red-blue. In some 
cases this change was quite pronounced and the colour became 
yellowish-red, almost blue, in other cases it was less marked and 
the yellow became only darker or more reddish-violet. The colours 
and particularly the order in which they occur during their formation 
and conversion are quite similar to those we observe with colloidal 
silver and photohaloids. *) Hence we cannot but think that likewise 
they all must be attributed to one and the same cause, viz. to the 
presence of small dispersed particles of the pure metal. 
The ultramieroscopic investigation bas quite corroborated this view. 
We also find this similarity in the case of gold. As early as 1857 
Farapay®) explicitly pointed this out in his classical experiments 
with extremely thin layers of gold and colloidal solution of gold. 
In both cases he accepted as an explanation that the colours were 
caused by small separate particles of the pure metal. 
Ultramicroscopic examination. We once more observed a splinter 
of the balloon with the aid of the ultramicroscope (Cardioideondenser). 
The red and the blue deposits and in many cases the vellow ones 
as well were optically quite soluble. They proved to consist of a 
closely connected network of ultramicrons, on the whole varying in 
colour, viz. blue, yellowish-brown, or green, the principal colour of 
which being complementary to the colour observed macroscopically; 
hence macroscopic: blue, ultramicroscopic: yellowishbrown; macrose.: 
1) W. Reinpers. Chem. Weekbl. 1910, 971 and 1001; Zeitschr, f. phys. Chem, 
77, -213,2006. 
2) M. Farapay. Bakerian Lecture, Phil. Trans. Roy. Soc. London, 147 (1857), 145, 
