28

FLUIDITY AND PLASTICITY

Bingham and White (1912) have confirmed the conclusion of
Knibbs by a study of interrupted flow. A capillary I = 9.38 cm
R = 0.01378 cm was used to determine the time of flow of a
given volume of water at 25° under a determined pressure. The
capillary was then broken squarely in two and the parts separated
by glass tubing, the whole being afterward covered with stout
rubber tubing. The time of flow was again determined under
the same conditions as before except that the corrections for
kinetic energy and for the effects of the ends of the tubes were
doubled by the interruption in the flow. The breaking of the
capillary was then repeated until the capillary was in six parts,
the corrections necessary being proportional to the number of
capillaries. For this case Eq. (10) becomes
irgR^pt mpVb

+ 6A)

6A)

= C

ML Z + 6A

where C and C; are constants under the conditions of experiment,
and b is the number of capillaries, and A as before is the fictitious
length, to be added to each capillary. Substituting in Eq. (12)
the values of the time of efflux and the pressure when the capillary
is unbroken ti and p\ and when broken t% and p% respectively,
we obtain the relation
I +6A

hence,

I -f A

K

TABLE X. — EXPEBIMENTS TO DETEEMINE THE "FICTITIOUS LENGTH"
OF A CAPILLARY XTKDEE CONDITIONS OF INTEERUPTED FLOW

Number of

Pressure in

capillaries 6
Time
grams
Cpt
K
A

per cm2

1
179.7
87.46
0.0836

2
* 180.2
87.77
0.0837
1.00
1+0.009

a
182.4
87.32
0.0835
0.99
9-0.006

4
183.1
87.75
0.0836
1.00
0 0.000

6
185.0
88.25
0.0838
1.00
2+0.003