A quartz flask (very small thermal expansion) holds water at 0 degrees centigrade (in an ice bath). The water fills the entire volume under the stopper and extends up into a capillary tube. When the flask is removed from the ice bath its temperature rises, as can be read on the thermometer. The water level in the capillary tube initially goes down, but reaches a minimum level at about 4 degrees and then rises as the temperature continues to increase. The photograph at the right is a close-up that permits both reading of the temperature and observation of the water volume.
This property of water is anomolous in that it is one of only a very few substances that behave in this manner.