  The surface tension of flowing soap films is measured with respect to the
film thickness and the concentration of soap solution. We perform this
measurement by measuring the curvature of the nylon wires that bound the soap
film channel and use the measured curvature to parametrize the relation between
the surface tension and the tension of the wire. We find the surface tension of
our soap films increases when the film is relatively thin or made of soap
solution of low concentration, otherwise it approaches an asymptotic value 30
mN/m. A simple adsorption model with only two parameters describes our
observations reasonably well. With our measurements, we are also able to
measure Gibbs elasticity for our soap film.
