962 
with the blue deposit, more of green with the red deposit, could 
any difference be observed. 
The difference was quite obvious however, in a few isolated 
cases, with a lamp where the evaporation of the silver had been 
effected by a very slow process and where the deposit had assumed 
a pale yellow colour. which by the influence of the air passed into 
violet. The field that had not been covered with Canada Balsam 
produced the brilliantly lighted mosaic of connected ultramicrons, 
while the protected field was optically hardly soluble, and but very 
faintly showed a similar network. The line of demarcation between 
the two fields was very marked. 
With the deposit of silver too, access of air results in a coarsening 
of structure, as we noticed before in the case of rocksalt. 
We have not been able to observe it utterly structureless, such 
as the layer of salt. Yet the possibility remains that the heating to 
60°, necessary to equally spread the considerably thickened Canada: 
Balsam, or even the mere contact with Canada Balsam is sufticient 
to prepare the passing into a more stable, granular condition and 
that the primarily formed greenish yellow deposit is structureless 
indeed, hence molecular-dispersed. 
It further appears that with an increasing thickness of the layer, 
even without access of air, the discontinuity, the construction from 
separate particles becomes more obvious. In this respect too, there 
is analogy between the deposit of silver and that of salt. 
The difference between the silver-film and the salt-film is a more 
gradual and a less essential one than seemed at first sight. In either 
case there arises primarily a thin layer of a great homogeneity, 
which, however, is unstable aud sbows a tendency to contract into 
separate particles. This tendency grows proportional to the increase 
of thickness and is also promoted by the presence of catalysers as 
vapour. With silver, however, the instability is much greater than 
with rocksalt; therefore we always find that with a very slight 
thickness deposits of silver are no longer homogeneous, but have 
separated into accumulations of small particles. 
In connection with KnupDsEn’s*) experiments on the influence of 
the temperature of condensation on the nature of the matter con- 
densed, we also modified the temperature of the bulb during the 
entire time of the burning. From his experiments KNUDsEN 
draws the conclusion that when metal-vapour molecules strike against 
a bulb, the chance of their being reflected is extremely slight, if 
1) Ann. d. Physik, (4) 50, 472 (1916). 
