964 
tint (e.g. coagulation of gold sol) the connection between these two - 
changes is not very clear, unless we take for granted that 
the totalcolour of the film is in the main that of a connected film, 
which both Farapay and Bemsy have noticed between the larger 
conglomerations. Our own observations are not contrary to this 
statement. The conversion of colour quite makes the impression as 
if the film had become thinner. But we have not been able to 
ascertain a discrete and thinner film *). 
Gold. Similarly as with silver in this ease too, thin deposits could 
be obtained, the colour of which first became pink, with prolonged 
sublimation blue and then green. 
Here again access of the air of the room resulted in a deepening 
of colour. ; 
When observed ultramicroscopically a mosaic of brownish-red, 
greenish or more bluish coloured ultramierons could again be discern- 
ed. The primary colour of this mosaic was complementary to the 
tint that was observed microscopically. So we see that on the whole 
this image bears a perfect resemblance to that of the deposit of silver. 
Tungsten. The deposit of tungsten differs considerably from the 
silver-deposit. 
Firstly it shows no colours, but immediately turns a muddy gray 
even with the thinnest layers. 
Secondly these films, even the quite dark ones are ultramicro- 
scopically utterly insoluble. 
The investigation of the tungsten deposits which had been obtained 
by cathodic atomizing proves that the power of reflection of tung- 
sten is in itself no impediment for the discrete particles being made 
perceptible, if only the latter are large enough (vide infra). So we 
must accept that the tungsten particles are much smaller than those 
of silver and gold. This admission is not a very improbable one. 
For in a normal temperature the vapour tension of tungsten is 
infinitely lower than that of gold or silver. Whereas a silverfilament 
glowing at a dull-red heat (600 ) produces a distinct deposit on the 
bulb, even after half an hour, we require a heat of nearly 3000° *) 
1) J. C. M. Garnetr (Phil. Trans. Roy Soc. London A. Pos. 237 1905)) tries 
to account for this change of colour by accepting that by heating the density of 
the layer decreases while consequently the volume of air, enclosed by the metal- 
particles increases. But such an assumption is not confirmed by any observation. 
®) With our tests we required for the formation of the tungsten deposit about 
6 hours, for the silver deposit from 30 minutes to 2 hours. 
