Surface Tension Determination through Capillary Rise and Laser Diffraction Patterns

In this physical chemistry experiment the surface tension of several solvents is measured. The surface tension is determined by measuring the height of the capillary rise in a capillary tube. The capillary tubing used is inexpensive, but its diameter is not known. The first part of the experiment involves measuring the capillary rise for several different solvents. The second part involves determining the radius of the tubing. A laser of known wavelength is passed through a short piece of the capillary tubing, creating a diffraction pattern. Assuming constant diameter, the radius of the tubing may then be calculated through measurements taken on the diffraction pattern. Students have used this method to determine the surface tension of several solvents with a relative error of less than 7 percent.