Calibration of the apparatus is done by determining tha capillary rise of deionized water , for which the temperature-dependent surface tension is well known. Add enough water to the bottom of the test tube so that the bottom of the capillary can easily be immersed in it. Install the stopper with the capillary in it and clamp whole setup so all parts of the apparatus containing water (including the water in the capillary) are immersed in the water bath.