[IGI 
emulsions. For that purpose are counted in the ultramicroscope the 
number of particles in a detinite volume-element. We have also 
done this with the ultra microscope (source of light self-regulating 
arc lamp according to Weurw, width of aperture 5, objective Zriss 
D*, compensation ocular 18, length of cylinder 16, Enrticn’s screen 
17). Dilutions were made in such a manner that never more than 
five particles were simultaneously present in the field of vision. In 
consequence of the Brownian movement the mean from a number 
of observations had to be taken. Generally a series of 20 observations 
was made four times. Below in Table 2 the list of the observations 
of one sol (N°. 2) is given; for the other sols the end results are 
given in Table 1. 
TABLE 2. 
Bie hy Bo aloe SED rl 2 Ale ie ba dee eed 
PERES Ro Dis Bik Be a. eee A aan 
NI Bh onl a by Bea |), 2a En aa 4 
fe aS, Rel dr Bk IA = Se Oil gee A eal 
oe EER 2 NEN A Oe BA Abe Soho ae ae Me 
| ni en Ee | 
| total 38 total 35 total 39 total 39 | 
| general average of 20 measurements 38 
These results cannot be interpreted in the same manner as those 
relating to gold sols. For there we see the luminous particles against 
a completely dark background. Here on the other hand we notice 
besides the partieles an undistinguishable pale blue illumination of 
the field. We therefore have particles of unequal size in the sol and 
we only count the large particles. If now at the different concentrations 
all was equal, we ought, on recalculating our results to one standard 
solution, to find figures which increase proportionally with the con- 
centration. Such figures are found in the last column of Table 1; they 
are so chosen that the concentration and standard figure in experiment 
2 are about equal. We now see at once that the number of large 
particles increases more rapidly than the concentration, therefore, 
the concentrated sols possess probably a smaller average dispersity 
degree than the diluted ones. This can be readily understood because 
the repeated boiling, in order to dissolve fresh As,O,, probably leads 
to enlargement of the particles. 
Nevertheless this result does not diminish the value of our con- 
