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LABORATORY EXPERIMENT № 9

DETERMINATION OF SURFACE TENSION OF
SURFACE-ACTIVE AGENTS (SURFACTANTS) WATER

SOLUTIONS AND ITS CHANGE DEPENDING ON
THE CONCENTRATION OF SURFACTANTS BY MEANS
OF A STALAGMOMETER METHOD

9.1. The objective of the experiment is: to study the methods of
measurement of the surface tension on the border of liquid with

another one and determine the surface tension of water solutions of

surfactants and its change depending on the concentration of
surfactants by means of a stalagmometer method and study the
peculiarities of the surface tension in oil and gas saturated formations.

9.2 Definitions

2
Surface tension is defined as forming 1 m of new surface of
liquid in isothermal conditions or as surplus of free energy of 1 m 2

of the surface layer of liquid comparing to the energy of the layer of
the same thickness taken inside of the liquid. The dimension (unit of
2
2
measurement) of surface tension is J/m or mJ/m . Besides surface
tension is also considered as the force referred to the length unit that
is to 1 m of the line limiting the surface of liquid. The second

dimension of surface tension is N/m or mN/m.
Such methods as static methods and semistatic methods of the
first and the second type are used for measuring the surface tension of

liquids (water solutions of surfactants).
1) static methods. They are based on the measuring the height

of the capillary rise or the sizes of bubble or drop (hanging or lying);
2) semistatic methods of the first type. They are based on the

comparing the forces of surface tension with gravitational ones (the
method of counting and weighing the drops);
3) semistatic methods of the second type. These methods are

based on measuring:
a) the force of tearing the ring, cylinder, plate away from the surface
of liquid;

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