FLUIDITY AND DIFFUSION 189

which are spheres and having a radius large in comparison with
the molecules of the solvent. If the particles are so small that
the free path a of the molecules of the suspending medium is ap-
preciable in comparison with the radius of the particles, Suther-
land (1905), Cunningham (1910) andMillikan (1910) have shown
that Stokes' formula becomes

0 =

RT

N

(64)

where A is a constant and equal to about 0.815.

The following table from Thovert (1904) indicates that the
product of the diffusion constant and the time of efflux is approxi-
mately constant for a considerable number of substances.

TABLE XLVIIL—THE

RELATION BETWEEN DIFFUSION AND VISCOSITY
(THOVERT)

Substance
<5 X 105
T, time of efflux
d X T X 104

Ether ........................
3 10
315
98

Oa,rbon disulfidc . . .
2 44
405
99

Chloroform ...... ....
1 50
660
99

Mixture ethyl alcohol and ether . Kenzene ..................
1.51 1 24
660 790
100
98

Methyl alcohol ................
1 16
820
95

Mixture ethyl alcohol and benzene ....
1.03
950
98

Water .......
0.72
1,330
96

Ethyl alcohol ............
0.59
1,620
96

Turpentine ................
0.48
2,020
97

A.m.yl alcohol .................
0.155
5,900
92

Grlycerol solution . . .
0.0104
94,000
98

On the other hand, Oeholm (1913) finds that 871 is not exactly
constant for a series of alcohols as compared with water when
glycerol is the diffusing substance. Oeholm thinks that associa-
tion and hydration will account for the variations, at least in part.
Bell and Cameron have applied Poiseuille's formula to diffusion
through capillary spaces and find that the distance y which a
liquid moves in a given time t is given by the formula yn = kt,