191 
I have endeavoured in two ways to demonstrate this continuity. 
1. by allowing V,O, particles to grow until they should have 
attained microscopic dimensions. 
2. by so modifying the conditions of formation of the crystals of 
substances, which in ordinary circumstances form distinctly observable 
erystals, that they can only attain ultramicroscopic: dimensions and 
by observing whether in this manner birefractive sols are formed 
also. . 
I. The growth of V,O, particles. 
lt is a well known phenomenon that colloidal or very finely 
divided crystalline precipilates gradually become crystalline or more 
coarsely crystalline when they are left in contact with the liquid 
in which they originated. 
A similar growth of the particles is also observable with the 
V,O, sol. The freshly prepared sol is but little turbid with incident 
light and does not, on shaking, exhibit the silky diffusions, or only 
so with exceedingly strong illumination. The old sol is visibly more 
turbid and exhibits the silky schliers. Ultramicroscopically, FRruNprIcH 
and DiesseLHORST found the first to be hardly or not at ail resolvable 
in ultramicrones, in the second they noticed very plainly the elon- 
gated particles. In the effect of the double refraction they found, 
however, no difference. No special attention, however, is devoted to 
this point. 
As the recrystallisation proceeds as a rule much more rapidly at 
a higher temperature than at a lower one, I have watched the 
change of the V,O, sol on heating on a water-bath. 
The sol was prepared by triturating 6 grams of NH,VO, in a 
morter with the equivalent quantity of 3 norm. HCl. After 10 minutes 
the liquid was filtered through a Bicnner funnel. Washing was 
continued until the filtrate became darker and the filter got clogged. 
The deposit was then again washed twice by decantation and then 
brought into colloidal solution by brietly shaking with 150 ec. of 
water. The’ following day it was separated from a very gelatinous 
deposit and filtered..The clear dark brownish-red solution contained 
12.4 grams of V,O, per Litre. | 
A portion was preserved at the ordinary temperature (IIa) and 
another portion heated on the water-bath in a Jena flask closed 
with a funnel (temp. 90°) the traces of waterevaporating thus being 
constantly replaced. After 1, 2'/,, 5 and 9 hours a part of the liquid 
was pipetted off and rapidly cooled. These portions are called 
IIb, llc, IId and Ile. 
