193 
freely moved about unrestrained, this was not the case here. Definite 
schliers of equally directed particles were very distinctly visible 
so that figures were formed which made one think of iron filings 
in a magnetic field or of hairs on a fur. A regularity in these 
figures is, however, wanting. 
In Ile this formation of schliers was still more stronger pro- 
nounced. The equally directed particles moved about in the schliers 
as in little water streams between more tranquil parts. Occasionally 
in such a stream an obstacle was visible round about which the 
stream divided in two, then again to unite to one whole. 
In a very convincing manner was thus brought here to light the 
inclination of the particles to arrange themselves all in the same 
direction, in streaming water. The schliers macroscopically visible 
in polarised light will be no doubt formed in a similar manner by 
particles. pointing in the same direction. In order to observe the 
influence of the dilution the quartz cuvette was cautiously opened 
and the sol present therein diluted with a drop of water when it 
was again examined under the microscope. The gelatinous mass had 
entirely disappeared; separate streams were no more to be seen 
and the whole field of vision was replete with the long needles in 
quite unrestrained motion such as was also the case with 115 and IIc. 
The entire experiment thus shows: 
1. in the freshly prepared sol the ultramicrones do not exhibit a 
one-sided growth, the long needles are wanting. 
2. on heating are formed needle-shaped ultramicrones of which 
the visible number and the size increases with the period of heating. 
3. the phenomenon of double refraction is very trifling with the 
sol one day old, but gets stronger on heating. 
4. The viscosity of the solution increases with the period of 
heating and finally there are formed quite transparent somewhat 
gelatinous lumps, which on dilution redissolve. 
The sol used in this experiment was rather concentrated and even 
without heating it changed after some days to such an extent that 
on stirring it gave a decided double refraction. As it was not exa- 
mined until one day after it had been prepared, the question whether 
entirely fresh sol was also birefractive remained unanswered. 
Therefore, a new sol was prepared, the precipitate being obtained 
from a strong solution of NH,VO, and hydrochloric acid. This precipitate 
was washed rapidly and brought into colloidal solution so that the 
sol was already filtered an hour after the precipitation and ready 
for investigation (Da). Per litre it contained 5.2 grams of V,O,. It 
also was very clear with incident light and gave no silky lustre 
13 
Proceedings Royal Acad. Amsterdam. Vol. XIX. 
