52

FLUIDITY AND PLASTICITY

Plastic Flow or the Fourth Regime.—When a mixture of liquids,
such as petroleum, is allowed to flow through a tube of large
diameter filled with finely porous material like Fuller's earth,
Gilpin1 and others have shown that there is a tendency for the
more volatile, i.e. the more fluid substances, to pass through
the maze of capillaries first, leaving the more viscous substances
behind. Naturally this effect is greatest when the pressure is
very small. It is easy to see that under such conditions of flow
the fluidity as calculated might appear quite abnormal. Just
as the fluidity appears abnormal when the velocity exceeds a
certain value and we pass into the second regime, so it appears
that the fluidity may appear abnormal when the velocity drops
below a certain critical value, and we pass into what may be
called the " Fourth KǤgirne."

"With homogeneous liquids or gases of high fluidity it is diffi-
cult to work at excessively low velocities, particularly on
account of the interference of dust particles. Very little work
has been done upon such substances having low fluidity, so that
for aught we know now the lower critical velocity may he ob-
servable only in mixtures.

Glaser (1907) measured the viscosity of colophonium-turpen-
tine mixtures by the transpiration method with the object of
testing the law of Poiseuille for very viscous and plastic sub-
stances. With one tube R = 0.49 cm, I = 10.5 crn he found

TABLE XVIII.-—THE VISCOSITY OF AN 85 PER CENT COLOPHONIUM—15
PER CEKT TURPENTINE MIXTURE AT 11.3° AND UNDER A CONSTANT
PRESSURE OF 2,040 CM WATER IN TUBES OP
VARIOUS DIAMETERS

R
I
t
y
77 X 107
<f> X 10-*

1.525
25.1
600
2.28
4.20
2.38

1.019
15.9
1,800
2.30
4.21
2.37

0.746
16.0
900
0.329
4.25
2.35

0.576
15.1
18,000
1.972
4.22
2.36

0.364
15.8
46,800
0.755
5.22
1.80

0,257
15.2
43,200
0.149
6.59
1.51

0.158
15.1
173,500
0.023
19.90
0.50

0.117
15.4
3 weeks
0.000
00
0.00

Am. Chem. J., 40, 495 (1908); 44, 251 (1910); 50, 59 (1913).