Page 19 - AN INTRODUCTION TO SURFACE CHEMISTRY By ERIC KEIGHTLEY RIDEAL

14 SURFACE TENSION OF LIQUIDS

In the light of the investigations of Rayleigh however it is
evident that the basic assumption as to the weight of an "ideal"
drop formed on the end of a tube of definite radius is erroneous.
A return to a more rational expression of the relation between
drop weight and surface tension has been made by Iredale (Phil.
Mag. XL. 1088, 1923). This expression rests upon the fact that
different liquids may form drops of similar shape from tubes of
different diameters, From this and from the assumption that
rupture occurs at the point of maximum concavity the equation
·°P
0+9
is developed, where o,, o, and p, p, are the surface tensions and
densities respectively of two liquids and K is the ratio of the radii
of the tubes from which symmetrical drops hang. All that is re-
quired for the practical determination of surface tension from this
formula" is a knowledge of the tube radius and drop radius ratio,
with a continuously varying radius of tube, for some standard
liquid of known surface tension and density" (Iredale, loc cit.).
From the data of Harkins on the drop weights of water from
tubes of varying radius we obtain the following data for the radius
of drops of water formed at tips of various sizes:
Tube radius r Drop radius r' r
in oms, for water ?

·09946 ·1998 4977
·14769 2238 ·0603
·19666 2425 ·8112
23790 2565 ·9863
27005 2669 1035
29694 ·2727 1088
·32362 ·2797 1·167
·37964 ·2938 1289
·44755 ·3103 1442
·55009 3351 643
·65031 ·3581 1816
·72229 ·3744 1929
·77329 ·3829 2019
·84892 ·3888 92184
10028 ·3900 2571
With the aid of this table and the equation of symmetry we are
in a position to calculate the surface tensions of other liquids from