222

FLUIDITY AND PLASTICITY

TABLE LVIII.—FRICTION AND MOBILITY OF A PAINT AS MEASURED BY

BlNGHAM AND GREEN1

FR
y

Pressure

dynes

Obser-

Num-
V-t centi-
grams
dynes
per

vations

ber of observation
meters per second
per Square centi-
per square centi-
square centimeter
F-f
M
Remarks
used in calculations

meter
meter

1
0.0005836
670.8
1030.7
98.2
938.7
0.260
Capillary S
1 and 2

2
0.0004557
537.8
826.3
84.6
734.3
0.260
r = 0.014486
2 and 3

cm

3
0.0003344
409.3
628.9
75.9
536.9
0.261
I = 4.620 cm
3 and 4

4
0.0002133
277.5
426.4
[66.0]
334.4
0.267

4 and 5

5
0.0001661
225.6
346.6
[57.7]
254 . G
0.273

5 and 6

6
0.0001019
152.9
234.9

7
0.002424
670.2
1458.6
101.0
1366.6
0.253
Capillary VI

8
0.001912
538.5
1171.9
85.4
1079.9
0.254
r = 0.020805

9
0.001418
409.5
891.2
87.5
799.2
0.255
1 = 4.684 cm
9 and 10

10
0.0008987
274.3
596.9
[65.6]
504.9
0.256

10 and 11

11
0.0004164
143.3
311.8
[53.7]
219.8
0.272

11 and 12

12
0.0002880
106.7
232.2

13
0 . 004638
671.7
1723.0
81.6
1631.0
0.246
Capillary III
13 and 14

14
0.003678
539.1
1382.9
93.2
1290.9
0.246
r = 0.02450
14 and 15

• 15
0 . 002726
409.0
1049.2
85.1
957.2
0.246
1 = 4.681 cm
15 and 16

16
0.001758
275.6
706.9
[75.1]
614.9
0.247

16 and 17

17
0.0008267
145.1
372.2
[63.5]
280.2
0.255

17 and 18

18
0.0005856
110.0
282.2

The average friction used in calculating the mobility is 92.0 dynes per square centimeter,
which gives an average mobility of 0.257. When the rate of flow V/t is too small, the
friction becomes smaller, as seen in the table and the last two values for each capillary may
well be neglected.
The Capillary Tube Method.—Unless the conditions of
flow are carefully chosen, the friction constant does not manifest
itself, or at any rate the amount of shear is not a linear function
of the shearing stress. This departure from linearity is very
often shown at the low rates of shear as indicated in Fig. 76
by the curve FG.
This peculiarity is not fully understood at present and the
worker will do well to avoid anxiety in regard to it by choosing
the conditions as nearly ideal as possible so that the flow will
be a linear function of the shearing stress.
Nevertheless the cause of the above peculiarity must be
investigated in detail if we are to understand fully the nature
1Proc. Am. Soc. for Test. Mats. (1919).