1625 
Chemistry. — “The Doublerefractive Sol of Vanadium Pentovide”. 
By Prof. H. R. Krurr. (Communicated by Prof. P. van RomBuren). 
(Communicated in the meeting of March 25, 1916). 
1. In the Jubilee Edition for Erster and Grrrer Diessennorst, 
Freunpiicu and Leonarvt’) have made highly interesting communications 
as to the V,O, sol. When dispersed colloidally in water, this substance 
gives a clear sol which, varying with the concentration, is from yellow 
to brown in transmitted light. [If this sol is stirred, there are noticed 
in the liquid, particularly in the case of specimens that have been 
kept for some months, peculiar, twinkling diffusions, which might 
lead the observer to think that a finely divided crystalline sediment 
were stirred up from the bottom. Curiously enough, the turbidity 
does not disappear in the direction of the bottom of the vessel but 
it often ceases to be visible just after it has still been noticed in the 
middle of the cuvette. Moreover, a deposit is always absent. 
If the sol is examined between crossed nicols, stirring seems to 
cause a clearer illumination of the field of vision; a continued 
investigation now taught that the sol when flowing in a definite 
direction behaves like a plate from a doublerefractive crystal. 
In the cardioid ultra-microscope, the sol appeared to consist of 
elongated rod-shaped particles. The above-cited observers now arrived 
at the following explanatory hypothesis: by currency, the particles 
get in the position which causes only the slightest friction with 
other liquid layers namely with their longitudinal axis parallel to 
the direction of the current. This causes an orientation which brings 
about the doublerefraction. 
They have made a series of experiments to state whether all 
phenomena were really in harmony with this surmise. Currency, 
magnetic field and galvanic current would presumably originate a 
ranging of the particles and indeed all the experiments which they 
carried out and in which they varied in all possible ways the vectors 
of the light-vibration and of the force applied to the system, seemed 
to lead to a light or dark field, just according to what was expected 
from the hypothesis. 
In a second paper”, DiesseLHorsT and FREUNDLICH could even 
1) DmussELHORST, FREUNDLICH and LrONHARDT, Arbeiten aus den Gebieten der 
Physik, Mathematik, Chemie, Junius ELsTER und Hans GEITEL gewidmet, pg! 
453— 478, Braunschweig 1915. 
2) DirsseLHORST and FREUNDLICH, Physikal. Zeitschr. 16, 419—425 (1915). See 
also Zeitschr. f. Elektrochemie 22, 27 —33 (1916). 
