452 
hk depends on distance. In order to calculate / from 7, we must 
know the total surface of the powder. It is impossible to measure 
this accurately, but where an estimate is sufficient, we can try to 
calculate it from the number of particles pro mgr. as described on 
page 446. 
We then assume, that the particles are spheres of equal dimensions 
and must know the specifie gravity of the selids. In this way I have 
found for the surface of 1 gr. 
quartzpowder 3260 cm? 
anorthitepowder 3150 em? 
In this way I have found for the relation between potential and 
distance the following numbers (4 expressed in cal. pro mol. adsorbed 
water) *): 
water -quartz (Si O,) water-anorthite (CaAl silicate) 
—k a Lin 10-® em. —k a Lin 106 om. 
328 0.0031 0.95 328 0.0185 5.87 
228 0.0633 LOL Zat ADS 0.0187 5.94 
128 0.0035 10 ODS 0,0188 5.97 
69.8 0.0039 1E) 69.8 0.01389 6.00 
36.0 0.0040 1.22 36.0 0.0191 6.06 
46.7 0.0041 1.25 1657 0.0199 6.32 
9.62 0.0042 1.28 9.62 0.0204 6.48 
3.86 0.0061 1.86 3.86 0.0253 8.03 
These tables represented graphically, give the figures shown below; 
it is, I believe, the first time, that it has been tried to determine 
experimentally the form of the law of molecular attraction. Many 
assumptions are made about it in theoretical physics, but nobody has 
so far tried to determine its form by actual measurement. The shape 
of the curve obtained, is not dependent on the exactness of the 
estimate of the surface of the powder; an error in this estimate can 
only lengthen or shorten the figure in the direction of the abscissae. 
It appears, that the potential diminishes rapidly with increasing 
distance and has a rather well defined “radius of the attraction- 
sphere” *). For the size of this radius we find: 
1) Hor LASNE 
2) We therefore come to the conclusion that the layer of fluid is almost in the 
whole course of the curve less thick than this radius. The supposition that the 
fluid has the properties of fluid in mass therefore only is exact as an 
approximation. 
