Page 15 - AN INTRODUCTION TO SURFACE CHEMISTRY By ERIC KEIGHTLEY RIDEAL

10 SURFACE TENSION OF LIQUIDS
rise for a tube of any diameter may be calculated (Sugden, J.0.S.
cx1X. 1483, 1921). This table is reproduced in part below:

r
r
- r - r
a i a b
0 I 0 I
01 9968 09 ·7875
02 9869 10 ·7490
03 9710 15 ·5545
04 9498 20 ·384
0-5 9236 3 ·149
06 ·8936 • 056
0-7 ·8606 5 020
08 ·8249 6 ·006

The capillary rise h, which has been discussed hitherto is of
course the height of the capillary meniscus above that of an
unbounded expanse of liquid, whose level is therefore unaffected
by surface tension, In practice it is not usually convenient to
employ so large a quantity of liquid as is demanded by this
condition, but instead two interconnected tubes one of capillary,
and one of wide bore are filled with liquid. The height h between
the two liquid levels is now the difference between two quantities
h, and h, defined by
2vcoea
I
)b'
99-p
and _ a cos a
•(oc-)b'
whence heh, hm as« .I)
.=e
9(P-P,) b, b'
To obtain reliable results it is essential in the first place to
ensure purity of the liquid and absolute cleanliness of the apparatus
especially from oily or greasy matter. The latter can most readily
be removed by treating the apparatus, after preliminary cleansing,
with warm aqua regia or chromic acid, and finally steaming for
about half an hour. The apparatus should therefore be designed
to facilitate this thorough cleaning. These conditions of course
apply equally to any method of measuring surface tensions.